{"id":471,"date":"2025-11-16T17:29:46","date_gmt":"2025-11-16T17:29:46","guid":{"rendered":"https:\/\/mdev-nexus-med-nus.pantheonsite.io\/nexus\/?post_type=learning-resource&#038;p=471"},"modified":"2026-04-23T10:51:09","modified_gmt":"2026-04-23T10:51:09","slug":"neurobiology","status":"publish","type":"learning-resource","link":"https:\/\/medicine.nus.edu.sg\/medixperience\/learning-resource\/neurobiology\/","title":{"rendered":"Neurobiology"},"content":{"rendered":"\n<h1>\n\t\tNeurobiology\n\t<\/h1>\n\t\tView Chapters\t\t\t\n\t\t\t\t\t<ul id=\"menu-ebook-neurobiology-left-side-menu\"><li id=\"menu-item-580\"><a aria-expanded=\"false\" href=\"#\">Chapter 1: Sensation and Perception, &#038; Fundamentals of Sensory System<\/a>\n<ul>\n\t<li id=\"menu-item-821\"><a href=\"#1-introduction-and-overview\">1. Introduction and Overview<\/a><\/li>\n\t<li id=\"menu-item-822\"><a href=\"#1-1-functions-of-sensory-systems\">1.1. Functions of Sensory Systems<\/a><\/li>\n\t<li id=\"menu-item-823\"><a href=\"#1-2-general-properties-of-sensory-systems\">1.2. General Properties of Sensory Systems<\/a><\/li>\n\t<li id=\"menu-item-824\"><a href=\"#1-3-sensory-receptors\">1.3. Sensory Receptors<\/a><\/li>\n\t<li id=\"menu-item-825\"><a href=\"#1-4-five-modes-of-sensory-detection\">1.4. Five Modes of Sensory Detection<\/a><\/li>\n\t<li id=\"menu-item-826\"><a href=\"#1-5-six-sensory-systems\">1.5. Six Sensory Systems<\/a><\/li>\n\t<li id=\"menu-item-827\"><a href=\"#1-6-stimulus-intensity\">1.6. Stimulus Intensity<\/a><\/li>\n\t<li id=\"menu-item-828\"><a href=\"#1-7-two-modes-of-receptor-adaptation\">1.7. Two Modes of Receptor Adaptation<\/a><\/li>\n\t<li id=\"menu-item-829\"><a href=\"#1-8-receptor-response\">1.8. Receptor Response<\/a><\/li>\n\t<li id=\"menu-item-830\"><a href=\"#1-9-receptive-fields-of-sensory-neurons\">1.9. Receptive Fields of Sensory Neurons<\/a><\/li>\n\t<li id=\"menu-item-831\"><a href=\"#1-10-mach-band-effect\">1.10. Mach Band Effect<\/a><\/li>\n\t<li id=\"menu-item-832\"><a href=\"#1-11-labeled-lines-hypothesis\">1.11. Labeled Lines Hypothesis<\/a><\/li>\n\t<li id=\"menu-item-820\"><a href=\"#1-12-how-does-the-CNS-integrate-sensory-information\">1.12. How does the CNS integrate sensory information?<\/a><\/li>\n\t<li id=\"menu-item-833\"><a href=\"#1-13-summary-general-properties-of-sensory-systems\">1.13. Summary: General Properties of Sensory Systems<\/a><\/li>\n\t<li id=\"menu-item-834\"><a href=\"#1-14-further-readings\">1.14. Further Readings<\/a><\/li>\n<\/ul>\n<\/li>\n<li id=\"menu-item-1184\"><a aria-expanded=\"false\" href=\"#\">Chapter 2: Special Senses (Taste, Smell and Hearing)<\/a>\n<ul>\n\t<li id=\"menu-item-1185\"><a href=\"#2-introduction-and-overview\">2. Introduction and Overview<\/a><\/li>\n\t<li id=\"menu-item-1186\"><a href=\"#2-1-what-is-taste\">2.1. What is Taste?<\/a><\/li>\n\t<li id=\"menu-item-1187\"><a href=\"#2-2-Mechanisms-of-Taste-Transduction\">2.2. Mechanisms of Taste Transduction<\/a><\/li>\n\t<li id=\"menu-item-1188\"><a href=\"#2-3-Oldest-Senses-Olfaction\">2.3. Oldest Senses &#8211; Olfaction<\/a><\/li>\n\t<li id=\"menu-item-1189\"><a href=\"#2-4-Mechanism-of-Olfactory-Transduction\">2.4. Mechanism of Olfactory Transduction<\/a><\/li>\n\t<li id=\"menu-item-1190\"><a href=\"#2-5-The-Ear-Hearing-and-Equilibrium\">2.5.  The Ear: Hearing and Equilibrium<\/a><\/li>\n\t<li id=\"menu-item-1191\"><a href=\"#2-6-Amplitude-and-Frequency-in-Sound-Waves\">2.6. Amplitude and Frequency in Sound Waves<\/a><\/li>\n\t<li id=\"menu-item-1192\"><a href=\"#2-7-Sound-Transmission-through-the-Ear\">2.7. Sound Transmission through the Ear<\/a><\/li>\n\t<li id=\"menu-item-1193\"><a href=\"#2-8-Signal-Transduction-in-Hair-Cells\">2.8. Signal Transduction in Hair Cells<\/a><\/li>\n\t<li id=\"menu-item-1194\"><a href=\"#2-9-Sensory-Coding-for-Pitch\">2.9. Sensory Coding for Pitch<\/a><\/li>\n\t<li id=\"menu-item-1195\"><a href=\"#2-10-Summary-Special-Senses\">2.10. Summary: Special Senses<\/a><\/li>\n\t<li id=\"menu-item-1196\"><a href=\"#2-11-Further-Readings\">2.11. Further Readings<\/a><\/li>\n<\/ul>\n<\/li>\n<li id=\"menu-item-1224\"><a aria-expanded=\"false\" href=\"#\">Chapter 3: Somatosensory System &#8211; Touch<\/a>\n<ul>\n\t<li id=\"menu-item-1232\"><a href=\"#3-introduction-and-overview\">3. Introduction and Overview<\/a><\/li>\n\t<li id=\"menu-item-1225\"><a href=\"#3-1-Primary-Afferent-Axons-and-The-Spinal-Cord-and-General-Projection-Pathway\">3.1. Primary Afferent Axons, Spinal Cord and General Projection Pathway<\/a><\/li>\n\t<li id=\"menu-item-1226\"><a href=\"#3-2-Mechanoreceptors-of-the-Skin\">3.2. Mechanoreceptors of the Skin<\/a><\/li>\n\t<li id=\"menu-item-1227\"><a href=\"#3-3-Thermoreceptors\">3.3. Thermoreceptors<\/a><\/li>\n\t<li id=\"menu-item-1228\"><a href=\"#3-4-Anatomical-Pathways\">3.4. Anatomical Pathways<\/a><\/li>\n\t<li id=\"menu-item-1229\"><a href=\"#3-5-Somatosensory-Cortex-and-Plasticity\">3.5. Somatosensory Cortex and Plasticity<\/a><\/li>\n\t<li id=\"menu-item-1230\"><a href=\"#3-6-Summary-Somatosensory-System-Touch\">3.6. Summary: Somatosensory System &#8211; Touch<\/a><\/li>\n\t<li id=\"menu-item-1231\"><a href=\"#3-7-Further-Readings\">3.7. Further Readings<\/a><\/li>\n<\/ul>\n<\/li>\n<li id=\"menu-item-1253\"><a aria-expanded=\"false\" href=\"#\">Chapter 4: Physiological and Patho-Physiological Basis of Pain<\/a>\n<ul>\n\t<li id=\"menu-item-1254\"><a href=\"#4-introduction-and-overview\">4. Introduction and Overview<\/a><\/li>\n\t<li id=\"menu-item-1255\"><a href=\"#4-1-Nociceptors-and-the-Transduction-of-Painful-Stimuli\">4.1. Nociceptors and the Transduction of Painful Stimuli<\/a><\/li>\n\t<li id=\"menu-item-1256\"><a href=\"#4-2-Referred-Pain-Viscerosomatic-Convergence\">4.2. Referred Pain: Viscerosomatic Convergence<\/a><\/li>\n\t<li id=\"menu-item-1257\"><a href=\"#4-3-Sensitisation-of-Peripheral-Receptors\">4.3. Sensitisation of Peripheral Receptors<\/a><\/li>\n\t<li id=\"menu-item-1258\"><a href=\"#4-4-Projection-of-Fibers-into-the-Spinal-Cord\">4.4. Projection of Fibers into the Spinal Cord<\/a><\/li>\n\t<li id=\"menu-item-1259\"><a href=\"#4-5-Principles-of-Central-Sensitisation-Wind-up\">4.5. Principles of Central Sensitisation &#8220;Wind-up&#8221;<\/a><\/li>\n\t<li id=\"menu-item-1260\"><a href=\"#4-6-Hyperalgesia-and-Allodynia\">4.6. Hyperalgesia and Allodynia<\/a><\/li>\n\t<li id=\"menu-item-1261\"><a href=\"#4-7-Ascending-Pain-Pathways\">4.7. Ascending Pain Pathways<\/a><\/li>\n\t<li id=\"menu-item-1262\"><a href=\"#4-8-Medial-Affective-Motivational-Pathway-vs-Lateral-Sensory-Discriminative-Pathway\">4.8. Medial Affective-Motivational Pathway vs Lateral Sensory-Discriminative Pathway<\/a><\/li>\n\t<li id=\"menu-item-1263\"><a href=\"#4-9-Gate-Control-Model-of-Pain-Modulation\">4.9. Gate Control Model of Pain Modulation<\/a><\/li>\n\t<li id=\"menu-item-1264\"><a href=\"#4-10-Conceptual-Overview-of-Pain-Modulation-Network\">4.10. Conceptual Overview of Pain Modulation Network<\/a><\/li>\n\t<li id=\"menu-item-1265\"><a href=\"#4-11-Endogenous-Opioid-System\">4.11. Endogenous Opioid System<\/a><\/li>\n\t<li id=\"menu-item-1266\"><a href=\"#4-12-Four-Main-Types-of-Pain\">4.12. Four Main Types of Pain<\/a><\/li>\n\t<li id=\"menu-item-1267\"><a href=\"#4-13-Summary-Pain\">4.13. Summary: Pain<\/a><\/li>\n\t<li id=\"menu-item-1268\"><a href=\"#4-14-Further-Readings\">4.14. Further Readings<\/a><\/li>\n<\/ul>\n<\/li>\n<\/ul>\t\n\t<h1>\n\t\tChapter 1: Sensation and Perception, &#038; Fundamentals of Sensory System\n\t<\/h1>\n\tAsst Prof Shuo-Chien Ling, Ph.D.<br \/>\nLaboratory of Molecular Neurodegeneration<br \/>\nNUS Yong Loo Lin School of Medicine Department of Physiology<br \/>\nEmail: <a href=\"mailto:phsling@nus.edu.sg\">phsling@nus.edu.sg<\/a>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/baZNVLIFbio\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t\t<h2>\n\t\tIntroduction\n\t<\/h2>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/undefined-3.png\" alt=\"Young child exploring pink flowers by touch, representing how we use our senses to experience the world\" itemprop=\"image\" height=\"624\" width=\"936\" title=\"undefined (3)\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Have you ever wondered how we sense and perceive the world &#8211; how the eyes see; the skin detect cold, heat, pain; the ears recognise certain sounds; the nose identify smells; and the mouth enjoy different tastes?<\/p>\n<p>In this e-Book, you will learn the science behind our senses and perception. Sensory neurophysiology will help you understand how we sense and perceive the world.<\/p>\n<h2>\n\t\tOverview\n\t<\/h2>\n\t<p>In this chapter, we will first focus on the types and functions of sensory system and the principles of organisation and processing of sensory information. We will also cover three special senses: taste, smell and hearing.<\/p>\n<p><strong>Learning Objectives<\/strong><\/p>\n<p>At the end of this chapter, you should be able to:<\/p>\n<ol>\n<li>\n1\nIdentify the types and explain the functions of sensory systems\n2\nExplain the principles of organisation and processing of sensory information\n<\/li>\n<\/ol>\n<h2>\n\t\t1.1. Functions of Sensory Systems\n\t<\/h2>\n<h3>\n\t\tThe function of each sensory system is to provide the central nervous system (CNS) with a representation of external world.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/senses.png\" alt=\"senses\" itemprop=\"image\" height=\"318\" width=\"702\" title=\"senses\" onerror=\"this.style.display='none'\"  \/>\n\t<p>The Greek philosopher Aristotle defined the five senses.<\/p>\n<p>We perceive sensory signals when they reach a level of conscious awareness.<\/p>\n<p>Stimulus that usually do not reach conscious awareness include changes in muscle stretch and tension as well as a variety of internal parameters that the body monitors to maintain homeostasis such as blood pressure and pH. These processes are important in maintaining physiological homeostasis.<\/p>\n<p>Hence, we will primarily consider sensory stimuli whose processing reaches the conscious level of perception.<\/p>\n<p>These stimuli are those associated with the special senses of vision, hearing, taste, smell and equilibrium, and the somatic senses of touch, temperature, pain, itch and proprioception. Proprioception, which is defined as the awareness of body movement and position in space, is mediated by muscle and joint sensory receptors call proprioceptors and may be either subconscious or conscious.<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/blonde-athlete-stretching-arms-with-eyes-closed-in-PUTMQ7C.png\" alt=\"blonde-athlete-stretching-arms-with-eyes-closed-in-PUTMQ7C\" itemprop=\"image\" height=\"466\" width=\"700\" title=\"blonde-athlete-stretching-arms-with-eyes-closed-in-PUTMQ7C\" onerror=\"this.style.display='none'\"  \/>\n\t<p>If you close your eyes and raise your arm above your head, you are aware of its position because of the activation of proprioceptors.<\/p>\n<h3>\n\t\tSensory systems bring the information to an individual.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/19.jpg\" alt=\"19\" itemprop=\"image\" height=\"390\" width=\"700\" title=\"19\" onerror=\"this.style.display='none'\"  \/>\n<h4>\n\t\tVideo 1: Sensory Systems\n\t<\/h4>\n\t<p>Watch the video below for more information.<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/YK40qwfaKyM\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t\t<h2>\n\t\t1.2. General Properties of Sensory Systems\n\t<\/h2>\n<h3>\n\t\tHow does the nervous system encode and process sensory stimuli?\n\t<\/h3>\n\t<p>Let&#8217;s first consider the general properties of sensory pathways. Here, we will take a look at unique receptors and pathways that distinguish the different sensory systems from one another and use three special senses, taste, smell and hearing as examples.<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/forest-AE5KP4N.png\" alt=\"forest-AE5KP4N\" itemprop=\"image\" height=\"466\" width=\"700\" title=\"forest-AE5KP4N\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Imagine that you are in the wild.<\/p>\n<p>What do you need to do to survive?<\/p>\n<p>Is there a lion or tiger hiding in the grass ready to eat you?<\/p>\n<p>You need to see, hear, smell, and feel. How does the nervous system do that?<\/p>\n<p>In essence, the sensory system needs to communicate the key features of any stimuli: what is the stimuli, where, how strong it is (intensity), the duration (for how long the stimuli is on). The type of stimuli, we call sensory modality, are vision, hearing, hearing, etc.<\/p>\n<p>All sensory pathways have certain elements in common. They begin with a stimulus, in the form of physical energy that acts on a sensory receptor. The receptor is a transducer that converts the stimulus into an intra-cellular signal, usually, a change in membrane potential. If the stimulus is above threshold, action potentials pass along a sensory neuron to the CNS, where incoming signals are integrated. At each synapse along the pathway, the nervous system can modulate and shape the sensory information.<\/p>\n<p><strong>Key Concepts<\/strong><\/p>\n<ul>\n<li>\n<ul>\n<li>Coding and processing distinguish stimulus properties<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li>\n<ul>\n<li>\n<ul>\n<li>Sensory modality (what?)<\/li>\n<li>Location of the stimulus (where?)<\/li>\n<li>Intensity (how much?)<\/li>\n<li>Duration\/timing (how long?)<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li>\n<ul>\n<li>Receptors are sensitive to particular forms of energy.<\/li>\n<li>Sensory transduction converts stimuli into graded potentials.<\/li>\n<li>A sensory neuron has a receptive field.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li>\n<ul>\n<li>\n<ul>\n<li>Lateral inhibition<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li>\n<ul>\n<li>The CNS integrates sensory information.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<ul>\n<li>\n<ul>\n<li>\n<ul>\n<li>Labeled line<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h2>\n\t\t1.3. Sensory Receptors\n\t<\/h2>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/neurons-PG8PZMF.png\" alt=\"neurons-PG8PZMF\" itemprop=\"image\" height=\"468\" width=\"700\" title=\"neurons-PG8PZMF\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Receptors are sensitive to particular forms of energy and receptor cells convert stimulus into electrical signals.<\/p>\n<h4>\n\t\tVideo 2: Sensory Receptors\n\t<\/h4>\n\t<p>Sensory receptors detect information from the environment, such as light and sound, or from our own bodies, such as touch and body position.<\/p>\n<p>Watch the video below for more information.<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/aKXWmcJjV6o\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p><em>Reference: (1) Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 3.5; (2) Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 8.11<\/em><\/p>\n\t<p>Sensory receptors act as transducers in that they transform a physical or chemical stimulus (or form of energy) into an electrical impulse. They are specialised to detect sensory information and translate stimuli into receptor potentials, or electrical signaling within the receptor, caused by the opening and closing of ion channels. Each sensory receptor has a receptive field, which lets us discriminate the location of the sensory stimulus.<\/p>\n<p>Receptor potentials, also referred to as generator potentials, are electrical impulses transduced by the sensory receptor. The receptor potential is a graded response that depends on the magnitude of the sensory stimulus and encodes for duration and intensity. Because a receptor potential dissipates after a few millimeters, an action potential must be generated to travel the long distance between the sensory receptor and the CNS. In order to generate an action potential, the depolarisation of the membrane at the sensory receptor must reach threshold. The firing frequency of the action potential in the sensory nerve is modulated by the receptor potential: The greater the stimulus, the greater the receptor potential, and the higher the frequency of action potentials produced.<\/p>\n<p>Voltage recordings from an olfactory receptor cell during stimulation.<\/p>\n<p>Odorants generate a slow receptor potential in the cilia; the receptor potential propagates along the dendrite and triggers a series of action potentials within the soma of the olfactory receptor cells. Finally, the action potentials (but not the receptor potential) propagate continuously along the olfactory nerve axon.<\/p>\n<h2>\n\t\t1.4. Five Modes of Sensory Detection\n\t<\/h2>\n<h3>\n\t\tThe source of the stimulus can be external or internal.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/12.png\" alt=\"12\" itemprop=\"image\" height=\"360\" width=\"700\" title=\"12\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Superficially\u00a0located\u00a0sensory endings in the skin are called exteroceptors and respond to pain temperature,\u00a0touch\u00a0and pressure, that is stimuli outside the body.\u00a0<\/p>\n<p>Muscles, tendons, and joints have proprioceptors that signal awareness of body position and movement.\u00a0<\/p>\n<p>Enteroreceptors monitor events within the body such as feeling movement through\u202f the gut. \u00a0<\/p>\n<h3>\n\t\tMode of detection can be grouped into five categories:\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/13-290x300.png\" alt=\"Chemoreceptors detect molecules that bind to the receptor, for example, in the olfactory bulb.\u00a0\" itemprop=\"image\" height=\"300\" width=\"290\" title=\"13\" onerror=\"this.style.display='none'\"  \/>\n\t\tChemoreceptors detect molecules that bind to the receptor, for example, in the olfactory bulb.\u00a0\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/14-289x300.png\" alt=\"Photoreceptors detect light in the retina.\u00a0\" itemprop=\"image\" height=\"300\" width=\"289\" title=\"14\" onerror=\"this.style.display='none'\"  \/>\n\t\tPhotoreceptors detect light in the retina.\u00a0\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/15-289x300.png\" alt=\"Thermoreceptors detect temperature in the skin.\u00a0\" itemprop=\"image\" height=\"300\" width=\"289\" title=\"15\" onerror=\"this.style.display='none'\"  \/>\n\t\tThermoreceptors detect temperature in the skin.\u00a0\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/16-292x300.png\" alt=\"Mechanoreceptors are stimulated by the mechanical opening of ion channels, for example, touch receptors in the skin.\u00a0\" itemprop=\"image\" height=\"300\" width=\"292\" title=\"16\" onerror=\"this.style.display='none'\"  \/>\n\t\tMechanoreceptors are stimulated by the mechanical opening of ion channels, for example, touch receptors in the skin.\u00a0\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/17-290x300.png\" alt=\"Nociceptors detect signals associated with tissue damage, which are interpreted as pain.\u00a0\" itemprop=\"image\" height=\"300\" width=\"290\" title=\"17\" onerror=\"this.style.display='none'\"  \/>\n\t\tNociceptors detect signals associated with tissue damage, which are interpreted as pain.\u00a0\n<h2>\n\t\t1.5. Six Sensory Systems\n\t<\/h2>\n<h3>\n\t\tReceptors are sensitive to particular forms of energy and receptor cells convert stimulus into electrical signals.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Picture1-1.png\" alt=\"Picture1 (1)\" itemprop=\"image\" height=\"354\" width=\"700\" title=\"Picture1 (1)\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Neurons of the brain and spinal cord do not respond when they are touched or when they are exposed to sound or light or odors. Each form of energy must be transduced by a population of specialised cells, which converts the stimulus into a signal that all neurons understand.<\/p>\n<p>In every sensory system, cells that perform this transduction step are called receptors. For each of the fundamental types of stimuli (mechanical, chemical, or thermal energy or light), there is a separate population of receptors selective for the particular form of energy.<\/p>\n<p>Even within a single sensory system, there are class of receptors that are particularly sensitive to one stimulus (e.g., heat or cold) and not another (muscle stretch). The specificity in the receptor response is a direct function of differences in receptor structure and chemistry.<\/p>\n<h2>\n\t\t1.6. Stimulus Intensity\n\t<\/h2>\n<h3>\n\t\tSensory neurons use action potential frequency and duration to code stimulus intensity and duration.\n\t<\/h3>\n<h4>\n\t\tVideo 3: Stimulus Intensity\n\t<\/h4>\n\t<p>The intensity of a stimulus can not be directly calculated from a single sensory neuron action potential.<\/p>\n<p>Watch the video below for more information.<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/eQA-TTWa5lU\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p><em>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.6<\/em><\/p>\n\t<p>The intensity of a stimulus can not be directly calculated from a single sensory neuron action potential because a single action potential is &#8220;all-or-none&#8221;. Instead, stimulus intensity is coded in two types of information: the number of receptors activated and the frequency of action potentials coming from those receptors (frequency coding).<\/p>\n<p>For individual sensory neurons, intensity discrimination begins at the receptor. If a stimulus is below threshold, the primary sensory neuron does not respond. Once stimulus intensity exceeds threshold, the primary sensory neuron begins to fire action potentials. As stimulus intensity increases, the receptor potential amplitude (strength) increase in proportion, and the the frequency of action potential in the primary sensory neurons increases, up to a maximum rate.<\/p>\n<p>Similarly, the duration of a stimulus is coded by the duration of action potentials in the sensory neuron. In general, a longer stimulus generate s a longer series of action potential.<\/p>\n<h2>\n\t\t1.7. Two Modes of Receptor Adaptation\n\t<\/h2>\n<h3>\n\t\tThe two modes of receptor adaptation include:\n\t<\/h3>\n\t<ol>\n<li aria-setsize=\"-1\" data-leveltext=\"%1.\" data-font=\"\" data-listid=\"3\" data-list-defn-props=\"{&quot;335552541&quot;:0,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769242&quot;:[65533,0],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;%1.&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">Tonic &#8211; slowly adapting\u00a0<\/li>\n<li>Phasic &#8211; rapidly adapting\u00a0<\/li>\n<\/ol>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/21.png\" alt=\"Sensory receptors become less responsive to a stimulus over time, which is a process known as receptor adaptation.\u00a0\" itemprop=\"image\" height=\"271\" width=\"468\" title=\"21\" onerror=\"this.style.display='none'\"  \/>\n\t\tSensory receptors become less responsive to a stimulus over time, which is a process known as receptor adaptation.\u00a0\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/22.png\" alt=\"Slowly adapting receptors (also known as tonic receptors): Slowly adapting receptors adapt very little\u00a0over time and remain responsive during long stimuli. These receptors are suited to monitor unchanging stimuli such as pressure.\u00a0\" itemprop=\"image\" height=\"271\" width=\"468\" title=\"22\" onerror=\"this.style.display='none'\"  \/>\n\t\tSlowly adapting receptors (also known as tonic receptors): Slowly adapting receptors adapt very little\u00a0over time and remain responsive during long stimuli. These receptors are suited to monitor unchanging stimuli such as pressure.\u00a0\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/23.png\" alt=\"Rapidly adapting receptors (also known as phasic receptors): Rapidly adapting receptors adapt very quickly and essentially detect only the onset of a stimulus. They are suited to detect rapidly changing impulses such as vibration.\u00a0\" itemprop=\"image\" height=\"271\" width=\"468\" title=\"23\" onerror=\"this.style.display='none'\"  \/>\n\t\tRapidly adapting receptors (also known as phasic receptors): Rapidly adapting receptors adapt very quickly and essentially detect only the onset of a stimulus. They are suited to detect rapidly changing impulses such as vibration.\u00a0\n\t<p>In general, the stimuli that\u00a0activate\u00a0tonic receptors are parameters that must be\u00a0monitored\u00a0continuously by the body. Once a stimulus reaches a steady intensity, phasic receptors adapt to a new steady state and turn off.\u00a0<\/p>\n<h2>\n\t\t1.8. Receptor Response\n\t<\/h2>\n<h3>\n\t\tReceptor response can decline with maintained stimuli: adaptation.\n\t<\/h3>\n\t<p>The rate of firing of this neuron, whose receptive field is located on the fifth finger, is rapid when the stimulus is first applied, but then adapts, slowing to a steady rate.<\/p>\n<h2>\n\t\t1.9. Receptive Fields of Sensory Neurons\n\t<\/h2>\n<h3>\n\t\tA sensory neuron has a receptive field.\n\t<\/h3>\n\t<p>Somatic sensory and visual neurons are activated by stimuli that fall within a specific physical area known as the neuron&#8217;s receptive field.<\/p>\n<h3>\n\t\tThe size of secondary receptive fields determines how sensitive a given area is to a stimulus.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/6.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.2\u00a0\" itemprop=\"image\" height=\"465\" width=\"702\" title=\"6\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.2\u00a0\n<h2>\n\t\t1.10. Mach Band Effect\n\t<\/h2>\n\t<p>The Mach Band Effect is named after Ernst Mach.\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/7.png\" alt=\"7\" itemprop=\"image\" height=\"376\" width=\"468\" title=\"7\" onerror=\"this.style.display='none'\"  \/>\n\tReference: <a href=\"https:\/\/en.wikipedia.org\/wiki\/Mach_bands\">https:\/\/en.wikipedia.org\/wiki\/Mach_bands<\/a><br \/>\nFor each block of the color, are they the same or gradient, or? What do you think you see?\n<h3>\n\t\tLateral inhibition enhances contrast and makes a stimulus easier to perceive.\n\t<\/h3>\n<h4>\n\t\tVideo 4: Lateral Inhibition\n\t<\/h4>\n\t<p>Lateral inhibition, which increases the contrast between activated receptive fields and their inactive neighbors, is another way of isolating the location of a stimulus.<\/p>\n<p>Watch the video below for more information.<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/EQX7dA9xTws\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.5\u00a0<\/p>\n<h2>\n\t\t1.11. Labeled Lines Hypothesis\n\t<\/h2>\n<h3>\n\t\tEach receptor (cold, warmth, touch, pain) has a distinct pathway linking the receptor surface to the brain, so different qualities of skin  stimulation can be communicated to distinct places in the brain. \n\t<\/h3>\n<h4>\n\t\tVideo 5: Labeled Lines\n\t<\/h4>\n\t<p>The brain associates a signal coming form a specific group of receptors with a specific modality. This 1:1 association of a receptor with a sensation is called labeled line coding.<\/p>\n<p>Watch the video below for more information.<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/oj81ZJ7ptsg\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t\t<h3>\n\t\tOne exception: the brain uses timing differences rather than specific neurons to localise sound.\n\t<\/h3>\n\t<p>Neurons in the ears are sensitive to different frequencies of sound, but they have no receptive\u00a0fields\u00a0and their activation provides no information about the location of the sound.<\/p>\n<p>How does the brain figure out where the sound is from?<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/18.png\" alt=\"The brain uses timing differences to\u00a0localise\u00a0sound.\u00a0\" itemprop=\"image\" height=\"687\" width=\"936\" title=\"18\" onerror=\"this.style.display='none'\"  \/>\n\t\tThe brain uses timing differences to\u00a0localise\u00a0sound.\u00a0\n<h2>\n\t\t1.12. How does the CNS integrate sensory information?\n\t<\/h2>\n<h3>\n\t\tThese are the sensory pathways in the brain. Most pathways except the  olfactory pathway pass through the thalamus on their way to the cerebral  cortex. \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/9.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.3\u00a0\" itemprop=\"image\" height=\"459\" width=\"702\" title=\"9\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.3\u00a0\n<h2>\n\t\t1.13. Summary: General Properties of Sensory Systems\n\t<\/h2>\n1\nEach receptor is most sensitive to a particular type of stimulus.\n2\nA stimulus above threshold initiates action potentials in a sensory neuron that projects to the CNS.\n3\nStimulus intensity and duration are coded in the pattern of action potentials reaching the CNS.\n4\nStimulus location and modality are coded according to which receptors are activated or (in the case of sound) by the timing receptor activation.\n5\nEach sensory pathway projects to a specific region of the cerebral cortex dedicated to a particular receptive filed. The brain can then tell the origin of each incoming signal.\n<h2>\n\t\t1.14. Further Readings\n\t<\/h2>\n\t<ol>\n<li>\n<ol>\n<li>Bears et al., Neuroscience: exploring the brain, 4th edition, chapter 8 and 11<\/li>\n<li>Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, chapter 3<\/li>\n<li>Silverthorn, Human Physiology, 5th edition, chapter 10<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<h1>\n\t\tChapter 2: Special Senses (Taste, Smell and Hearing)\n\t<\/h1>\n<h2>\n\t\tIntroduction\n\t<\/h2>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Smell.jpg\" alt=\"Smell\" itemprop=\"image\" height=\"572\" width=\"857\" title=\"Smell\" onerror=\"this.style.display='none'\"  \/>\n\t<p><em>How does the body perceive any smell, taste or sound?<\/em><\/p>\n<p><em>How does the brain process and identify each of them?<\/em><\/p>\n<h2>\n\t\tOverview\n\t<\/h2>\n\t<p>In this chapter, we will look at the Special Senses, which include Chemoreception (Smell and Taste) and The Ear (Hearing).<\/p>\n<p><strong>Learning Objectives<\/strong><\/p>\n<p>At the end of this chapter, you should be able to:<\/p>\n<ol>\n<li>\n1\nDescribe the function of chemoreception and hearing\n2\nIdentify\u00a0the five taste sensations\n3\nExplain the function of olfactory receptor cells\n4\nDescribe how sound is processed from the ear to the brain\n<\/li>\n<\/ol>\n<h2>\n\t\t2.1 What is Taste?\n\t<\/h2>\n<h3>\n\t\tTaste is a combination of five basic sensations. \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Microscopic-View-of-Taste-Bud.png\" alt=\"Microscopic View of Taste Bud\" itemprop=\"image\" height=\"363\" width=\"757\" title=\"Microscopic View of Taste Bud\" onerror=\"this.style.display='none'\"  \/>\n\t\tMicroscopic View of Taste Bud \n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.14\u00a0<\/p>\n\t<p>Taste is a combination of five sensations: sweet, sour, salty, bitter and &#8220;umami&#8221;, a taste associated with the amino acid glutamate and some nucleotides. &#8220;Umami&#8221; is a Japanese word which means deliciousness.\u00a0\u00a0<\/p>\n<p>The receptors for taste are located primarily on taste buds clustered together on the surface of the tongue. One taste bud is composed of 50-150 taste cells.\u202f\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Taste-Cell.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.14 \" itemprop=\"image\" height=\"367\" width=\"660\" title=\"Taste Cell\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.14 \n\t<p>Each taste cell is a non-neural polarised epithelial cell tucked own into the epithelium so that only tiny tip protrudes into the oral cavity through a taste pore.\u00a0In a given\u00a0bud, tight junctions link the apical ends of adjacent cells together, limiting movement of molecules between the cells. The apical membrane of a taste cell is\u00a0modified\u00a0into microvilli to increase the amount of surface area in contact with the environment.\u00a0\u00a0<\/p>\n<p>For a substance to be tasted, it must first dissolve in the saliva and mucus of the mouth. Dissolved taste ligands then interact with an apical membrane protein (receptor or channel) on a taste cell. Interaction of a taste ligand with a membrane protein\u00a0initiates\u00a0a signal transduction cascade that ends with a series of action potentials in primary neurons.\u202f\u00a0<\/p>\n<h2>\n\t\t2.2. Mechanisms of Taste Transduction\n\t<\/h2>\n<h3>\n\t\tThe transduction mechanism for salt and sour tastants is different from the transduction mechanism for bitter, sweet and &#8220;umami&#8221; tastants. \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Mechnisms-of-Taste-Transduction.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 8.7\u00a0\" itemprop=\"image\" height=\"442\" width=\"700\" title=\"Mechnisms of Taste Transduction\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 8.7\u00a0\n\t<p><b><i>Transduction Mechanisms of Salt and Sour\u00a0Tastants<\/i><\/b>\u00a0<\/p>\n<p>Tastants\u00a0can interact directly with ion channels either by passing through them (Na+ and H+) or by blocking them (H+ blocking the potassium channel). The membrane voltage then influences calcium channels on the basal membrane, which in turn influence the intracellular Ca2+ and transmitter release.\u202f\u00a0<\/p>\n<p><b><i>Transduction Mechanisms of Bitter, Sweet, and &#8220;Umami&#8221;\u00a0Tastants<\/i><\/b>\u00a0<\/p>\n<p>Tastants\u00a0can interact directly with G-protein coupled membrane receptors, which activate phospholipase C, which increase the synthesis of IP3. IP3 then triggers the release of Ca2+ from internal storage sites, and Ca2+ opens a taste-specific ion channel, leading to depolarisation and transmitter release. The main transmitter is ATP, which is released from the taste cell by diffusing through ATP-permeable channels.\u202f\u00a0<\/p>\n<h2>\n\t\t2.3. Oldest Senses &#8211; Olfaction\n\t<\/h2>\n<h4>\n\t\tVideo 6: Olfaction is One of the Oldest Senses\u00a0\n\t<\/h4>\n\tWhat defines an olfactory system? What does it do?<br \/>\n<br \/>\nWatch the video below for more information.\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Screenshot-111429.png\" alt=\"\"\/>\n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.13\u00a0<\/p>\n<h2>\n\t\t2.4. Mechanism of Olfactory Transduction\n\t<\/h2>\n<h4>\n\t\tVideo 7: Mechanism of Olfactory Transduction\u00a0\n\t<\/h4>\n\tHave you wonder how the function of smell happen in human beings?<br \/>\n<br \/>\nWatch the video below for more information.\u00a0\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/sIroxjyYWV8\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 8.10\u00a0<\/p>\n<h2>\n\t\t2.5.  The Ear: Hearing and Equilibrium\n\t<\/h2>\n<h3>\n\t\tThe ear is a sense organ that is specialised for two distinct functions: hearing and equilibrium. \n\t<\/h3>\n\t<p>It can be divided into external,\u00a0middle and inner sections. With the neurological elements housed in and protected by structures in the inner ear. The vestibular complex of the inner ear is the primary\u202fsensor for equilibrium. The reminder of the ear is used for hearing.\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Anatomy-of-Ear.png\" alt=\"Anatomy of Ear \" itemprop=\"image\" height=\"387\" width=\"697\" title=\"Anatomy of Ear\" onerror=\"this.style.display='none'\"  \/>\n\t\tAnatomy of Ear \n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.15<\/p>\n\t<p>The external ear consists of the outer ear, or pinna, and the ear canal. The pinna is another example of an important accessory structure to a sensory system, and it varies in shape and location from species to species, depending on the animals survival needs. The ear canal is sealed at its internal end by a thin membranous sheet of tissue called the tympanic membrane, or eardrum. \u00a0<\/p>\n<p>The tympanic membrane separates the external ear from the middle ear, an air-filled cavity that connects with the pharynx through the eustachian tube. The eustachian tube is normally collapsed, sealing off the middle ear, but it opens transiently to allow middle ear pressure to equilibrate with atmospheric pressure during chewing, swallowing, and yawn-ing. Colds or other infections that cause swelling can block the eustachian tube and result in fluid buildup in the middle ear. If bacteria are trapped in the middle ear fluid, the ear infection known as otitis media [oto-, ear * -itis, inflammation * media, middle] results.\u00a0\u00a0<\/p>\n<p>Three small bones of the middle ear conduct sound from the external environment to the inner ear: the malleus [hammer], the incus [anvil], and the stapes [stirrup]. The three bones are connected to one another with the biological equivalent of hinges. One end of the malleus is attached to the tympanic membrane, and the stirrup end of the stapes is attached to a thin membrane that separates the middle ear from the inner ear.\u00a0\u00a0<\/p>\n<p>The inner ear consists of two major sensory structures. The vestibular apparatus with its semicircular canals is the sensory transducer for our sense of equilibrium. The cochlea of the inner ear contains sensory receptors for hearing. On external view the cochlea is a membranous tube that lies coiled like a snail shell within a bony cavity. Two membranous disks, the oval window (to which the stapes is attached) and the round window, separate the liquid-filled cochlea from the air-filled middle ear. Branches of cranial nerve VIII, the vestibulocochlear nerve, lead from the inner ear to the brain. \u00a0<\/p>\n<h2>\n\t\t2.6. Amplitude and Frequency in Sound Waves\n\t<\/h2>\n<h3>\n\t\tSound waves alternate peaks of compressed air and valleys where the air is less compressed.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Frequency-in-Sound-Waves.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.16 \" itemprop=\"image\" height=\"352\" width=\"686\" title=\"Frequency in Sound Waves\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.16 \n\t<p>Hearing is our perception of the energy carried by sound waves, which are pressure waves with alternating peaks of compressed air and valleys in which the air molecules are farther apart.\u202f\u00a0<\/p>\n<p>Sound is the brain&#8217;s interpretation of the frequency, amplitude, and duration of sound waves that reach our ears. Our brain translate frequency of sound waves (the number of wave peaks that pass a given point each second) into the pitch of a sound. Low-frequency waves are perceived as low-pitched sounds, such as the rumble of distant thunder. High-frequency waves create high-pitched sounds, such as the screech of finger-nails on a blackboard.\u00a0<\/p>\n<h3>\n\t\tSound waves are distinguished by their Amplitude (in dB) and Frequency (in Hz).\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Sound-Waves.png\" alt=\"Sound Waves\" itemprop=\"image\" height=\"658\" width=\"700\" title=\"Sound Waves\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Sound wave frequency is measured in waves per second, or hertz (Hz). The average human ear can hear sounds over the frequency range of 20-20,000 Hz, with the most acute hearing between 1000-3000 Hz. Bats listen for ultra-high-frequency sound waves (in the kilohertz range) that bounce off objects in the dark. Elephants and some birds can hear sounds in the infrasound (very low\u00a0frequency) range.\u00a0\u00a0<\/p>\n<p>Loudness is our interpretation of sound intensity and is influenced by the sensitivity of an individual&#8217;s ear. The intensity of a sound wave is a function of the wave amplitude. Intensity is measured on a logarithmic scale in units called decibels (dB). Each 10-db increase represents a 10-fold increase in intensity. \u00a0<\/p>\n<p>Normal conversation has a typical noise level of about 60dB. Sounds of 80 dB or more can damage the sensitive hearing receptors of the ear, resulting in hearing loss.\u202f\u00a0<\/p>\n<h2>\n\t\t2.7. Sound Transmission through the Ear\n\t<\/h2>\n<h4>\n\t\tVideo 8: Sound Transmission Through the Ear\u00a0\n\t<\/h4>\n\tHearing is a complex sense that involves multiple transductions.<br \/>\n<br \/>\nWatch the video below for more information.\u00a0\u00a0\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/KVb6i_XZ7Mk\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.17\u00a0<\/p>\n<h2>\n\t\t2.8. Signal Transduction in Hair Cells\n\t<\/h2>\n<h4>\n\t\tVideo 9: Signal transduction in hair cells\u00a0\n\t<\/h4>\n\t<p>Hair cells are non-neural receptor cells. The surface of each hair cell\u00a0have\u00a0about 50-100 stiffened cilia. The longest cilium is connected a tectorial membrane. If the tectorial membrane moves, the cilia does it too.\u00a0\u00a0<\/p>\n<p>Watch the video below for more information.\u00a0\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/8n0jOJXQVd0\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.19<\/p>\n<h2>\n\t\t2.9. Sensory Coding for Pitch\n\t<\/h2>\n<h3>\n\t\tThe basilar membrane has variable sensitivity to sound wave frequency along the length. \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Sensory-Coding.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.20 \" itemprop=\"image\" height=\"287\" width=\"702\" title=\"Sensory Coding\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.20 \n\t<p>The auditory system processes sound waves so that they can be discriminated by location, pitch and loudness. \u00a0<\/p>\n<p>Initial processing for pitch and loudness takes place in the cochlea of each ear.\u00a0\u00a0<\/p>\n<p>Coding sound for pitch is primarily a function of the basilar membrane. The membrane is tiff and narrow near its attachment between the round and oval windows but widens and becomes more flexible near its distal end.\u00a0\u00a0<\/p>\n<h3>\n\t\tThe frequency of sound waves determines the displacement of the basilar membrane. The location of active hair cells creates a code that the brain translates as information about the pitch of sound. \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Frequency-of-Sound-Waves-Determines-Displacement-.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.20 \" itemprop=\"image\" height=\"541\" width=\"466\" title=\"Frequency of Sound Waves Determines Displacement\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.20 \n\t<p>High frequency waves entering the vestibular duct create maximum displacement of the basilar membrane close to the oval window and consequently are not transmitted very far along the cochlea. Low-frequency wave travel along the length of the basilar membrane and create their maximum displacement near the flexible distal end. The differential response to frequency transforms the temporal aspect of frequency (numbers of sound waves per second) into spatial coding for pitch by location along the basilar membrane. \u00a0<\/p>\n<p>A good analogy is a piano keyboard, where the location of a key tells\u00a0you\u00a0its pitch. The spatial coding of the basilar membrane is preserved in the auditory cortex as neurons project from hair cells to corresponding regions in the brain.\u00a0\u00a0<\/p>\n<p>Loudness is coded by the ear in the same way the signal strength is coded in somatic receptors.\u202f\u00a0<\/p>\n<h2>\n\t\t2.10. Summary: Special Senses\n\t<\/h2>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Chemoreception: Smell and Taste<\/h5>\n1\nChemoreception is divided into the special senses of smell (olfaction) and taste (gustation).\n2\nTaste is a combination of five sensations: sweet, sour, salty, bitter and &#8220;umami&#8221;.\n3\nTaste cells are non-neural cells with membrane channels or receptors that interact with taste ligands. This interaction creates an intracellular Ca2+ signal that ultimately activates the primary sensory neuron.\n4\nOlfactory receptor cells in the nasal cavity are bipolar neurons whose pathways project directly to the olfactory cortex.\n5\nOdorant receptors are G protein-coupled membrane proteins.\n\t\t\t\t\t\t<h5 tabindex=\"0\">The Ear: Hearing<\/h5>\n1\nHearing is our perception of the energy carried by sound waves. Sound transduction turns air waves into mechanical vibrations, then fluid waves, chemical signals, and finally action potentials.\n2\nWhen sound bends hair cell cilia, the hair cell membrane potential changes and alters release of neurotransmitter onto sensory neurons.\n3\nThe initial processing of pitch, loudness, and duration of sound takes place in the cochlea. Localisation of sound is a higher function that requires sensory input from both ears and sophisticated computation by the brain.\n\u00a0\n<h2>\n\t\t2.11. Further Readings\n\t<\/h2>\n\t<ol>\n<li>\n<ol>\n<li>Bears et al., Neuroscience: exploring the brain, 4th edition, chapter 8, 11 and 12<\/li>\n<li>Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, chapter 22<\/li>\n<li>Silverthorn, Human Physiology, 5th edition, chapter 10<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<h1>\n\t\tChapter 3: Somatosensory System &#8211; Touch\n\t<\/h1>\n<h2>\n\t\tIntroduction\n\t<\/h2>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/3-Introduction-.png\" alt=\"3-Introduction\" itemprop=\"image\" height=\"617\" width=\"927\" title=\"3-Introduction\" onerror=\"this.style.display='none'\"  \/>\n\t<p><em>Have you wondered how every object you touch feels different? <\/em><\/p>\n<p><em>Why do you react in a certain when you touch cold and hot object? <\/em><\/p>\n<h2>\n\t\tOverview\n\t<\/h2>\n\tIn this chapter, we will look at the Somatosensory system, the part of sensory nervous system associated with the four somatosensory modalities: <strong><em>Touch, Proprioception, Temperature and Nociception<\/em>.<\/strong>\n<b><br \/>\nLearning Objectives<\/b>\n\tAt the end of this chapter, you should be able to:\n1\nDescribe the general projection pathway to spinal cord\n2\nIdentify various mechanoreceptors of the skin, its functions and explore the mechanosensitive of the receptors of the skin\n3\nCorrelate the thermoreceptors and its reactions in humans\n4\nExplain the anatomical structure of the spinal cord and its roots, the segmental and longitudinal organisation of spinal cord and the dorsal column-medical leminiscal pathway\n5\nAnalyse the somatosensory cortex, somatotopic map plasticity, and presence of phantom limb sensations\n<h2>\n\t\t3.1. Primary Afferent Axons, Spinal Cord and General Projection Pathway\n\t<\/h2>\n\t<p><em>How does your body know how and when to react to a touch stimuli?\u00a0 <\/em><\/p>\n<h3>\n\t\tPeripheral Nervous System (PNS)\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Peripheral-Nervous-System.png\" alt=\"Reference: Krebs et al., Lippincott's Illustrated Reviews: Neuroscience, Figure 5.3 \" itemprop=\"image\" height=\"270\" width=\"710\" title=\"Peripheral Nervous System\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 5.3 \n\t<p>Sensory information enters the spinal cord through the posterior roots. Sensory cell bodies lie in the spinal ganglion of each spinal nerve. Motor information leaves the spinal cord through the anterior roots, and LMNs\u00a0are located in the anterior horn at each spinal level.\u00a0Each segment of the spinal cord innervates a specific area of skin, referred to as a\u00a0<strong>dermatome<\/strong>, and a specific muscle group, referred to as a\u00a0<strong>myotome<\/strong>. Primary efferent autonomic\u00a0fibers\u00a0have their cell bodies in the lateral horn and leave the spinal cord through the anterior root.The afferent autonomic\u00a0fibers\u00a0travel with the somatic afferents through the posterior root.\u202f\u00a0<\/p>\n<h3>\n\t\tPathway for Somatic Perception\n\t<\/h3>\n<h4>\n\t\tVideo 10: Somatic Perception to Somatosensory Cortex and Cerebellum \n\t<\/h4>\n\t<p>Sensory systems bring the information to an individual. The pathways for somatic perception projects to the somatosensory cortex and cerebellum.<\/p>\n<p>Watch the video below for more information.\u00a0\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/5ggYwgTb8-c\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.8 and 10.9<\/p>\n<h2>\n\t\t3.2. Mechanoreceptors of the Skin\n\t<\/h2>\n<h3>\n\t\tTouch receptors respond to many different stimuli.\n\t<\/h3>\n<h4>\n\t\tVideo 11: Touch Receptors in the Skin\n\t<\/h4>\n\t<p>The receptors are distributed throughout the body. Of all, the touch receptors are among the most common receptors in the body. \u00a0<\/p>\n<p>With the various forms of touch receptors, watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/UQlu_eQuDtg\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t\t<h3>\n\t\tReceptive Fields of Human Sensory Receptors Test \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Receptive-Fields-of-Human-Sensory-Receptors.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.2 \" itemprop=\"image\" height=\"323\" width=\"462\" title=\"Receptive Fields of Human Sensory Receptors\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.2 \n\t<p>By introducing a microelectrode into the media nerve of the arm, it is possible to record the action potentials from a single sensory axon and map its receptive field on the hand with a fine stimulus probe.\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/single-sensory-axon-mapping.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.2 \" itemprop=\"image\" height=\"361\" width=\"477\" title=\"single sensory axon mapping\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.2 \n\t<p>Results show that receptive fields are either relatively small\u00a0as in Messner&#8217;s corpuscles, or large, as in Pacinian Corpuscle.\u202f\u00a0<\/p>\n<h3>\n\t\tSensory Receptors\n\t<\/h3>\n<h4>\n\t\tVideo 12: Sensory Receptors in the Skin\n\t<\/h4>\n\t<p>Sensory receptors exist in all layers of the skin. There are four primary mechanoreceptors in human skin:\u202f\u00a0<b><i>Meissner&#8217;s corpuscles, Merkel cells, Pacinian\u00a0corpuscle\u00a0and Ruffini endings.<\/i><\/b>\u00a0<\/p>\n<p>Watch the video below for more information.<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/52J3sbIIhOk\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t\t<h3>\n\t\tMechanosensitive Ion Channels\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Mechanosensitive-Ion-Channels.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.6 \" itemprop=\"image\" height=\"277\" width=\"473\" title=\"Mechanosensitive Ion Channels\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.6 \n\t<p>Some membrane ion channels are sensitive to stretching of the lipid membrane, tension in the membrane directly induced the channel to open and allow cations to flow.\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Mechanosensitive-Ion-Channels-2.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.6 \" itemprop=\"image\" height=\"287\" width=\"473\" title=\"Mechanosensitive Ion Channels 2\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.6 \n\t<p>Other ion channels open when force is applied to extracellular structures linked to the channels by peptides.\u00a0\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Mechanosensitive-Ion-Channels-3.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.6 \" itemprop=\"image\" height=\"306\" width=\"502\" title=\"Mechanosensitive Ion Channels 3\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.6 \n\t<p>Mechanically sensitive channels may also be linked to intracellular proteins, especially those of the cytoskeleton; deformation of the cell and stress on its cytoskeleton generate forces that regulate channel gating.\u202f\u00a0<\/p>\n<h2>\n\t\t3.3. Thermoreceptors\n\t<\/h2>\n<h3>\n\t\tTemperature Receptors as Free Nerve Endings\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Temperature-Receptors-.png\" alt=\"Temperature Receptors\" itemprop=\"image\" height=\"152\" width=\"487\" title=\"Temperature Receptors\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Temperature receptors are free nerve endings that\u00a0terminate\u00a0in the subcutaneous layers of the skin. Cold receptors are sensitive primarily to temperatures lower than body temperature. Warm receptors are stimulated by temperatures in the range extending from normal body temperature (37\u00b0\u00a0C) to about 45\u00b0\u00a0C. Above that temperature, pain receptors are activated, creating a sensation of painful heat.<\/p>\n<h3>\n\t\tThermoreceptor Transient Receptor Potential (TRP) Channels \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Thermoreceptor-Transient-Receptor.png\" alt=\"Thermoreceptor TRP channels tuned to detect different temperatures. \" itemprop=\"image\" height=\"350\" width=\"467\" title=\"Thermoreceptor Transient Receptor\" onerror=\"this.style.display='none'\"  \/>\n\t<p>Thermoreceptor TRP channels tuned to detect different temperatures.<\/p>\n<p>Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.35<\/p>\n\t<p>The arrangement of the known thermosensitive TRP channel protein molecules in the neuronal membrane. TRPM8 and TRPV1 are responsive to menthol and capsaicin, respectively.\u00a0<\/p>\n<p>The graph plots the activation of the various TRP channels as a function of temperature.\u00a0<\/p>\n<h3>\n\t\tAdaptations of Thermoreceptors \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Adaptations-of-Thermoreceptors-.png\" alt=\"Adaptations of Thermoreceptors\" itemprop=\"image\" height=\"251\" width=\"497\" title=\"Adaptations of Thermoreceptors\" onerror=\"this.style.display='none'\"  \/>\n\t<p>The receptive field for a thermoreceptor is about 1 mm in diameter, and the receptors are scattered across the body. There are considerably more cold receptors than warm ones. Temperature receptors slowly adapt between 20\u00b0 and 40\u00b0 C. Their initial response tells us that the temperature is changing, and their sustained response tells us about the ambient temperature. \u00a0<\/p>\n<p>Outside the 20-40\u00b0\u00a0C range, where the likelihood of tissue damage is greater, the receptors do not adapt.\u00a0\u00a0<\/p>\n<p>Adaptations of thermoreceptors. The responses of cold and warm receptors to a step reduction in skin temperature are shown. Both receptors are most responsive to sudden changes in temperature, but they adapt over several seconds. \u00a0<\/p>\n<p>Cold receptors are coupled to A-delta and C\u00a0fibers, while warm receptors are coupled only to C\u00a0fibers.\u202f\u00a0<\/p>\n<h2>\n\t\t3.4. Anatomical Pathways\n\t<\/h2>\n<h3>\n\t\tStructure of\u202fA Segment of The Spinal Cord and Its Roots\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Structure-of-a-Segment-of-The-Spinal-Cord.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.10 \" itemprop=\"image\" height=\"397\" width=\"682\" title=\"Structure of a Segment of The Spinal Cord\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.10 \n\t<p>The spinal cord is made of\u00a0gray\u00a0and white matter. The\u00a0gray\u00a0matter,\u00a0located in the central part of the spinal cord, is shaped like a butterfly. The white matter surrounds the\u00a0gray\u00a0matter and is made of axons. These axons\u00a0contains pathways that connects the brain with the other parts of the body.\u00a0<\/p>\n<p>The pathway in red shows the path taken by the primary afferent axons. We will take a closer look at the primary afferent axons in the next segment.\u00a0<\/p>\n<h3>\n\t\tPrimary Afferent Axons\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Primary-Afferent-Axons.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.9 \" itemprop=\"image\" height=\"520\" width=\"472\" title=\"Primary Afferent Axons\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.9 \n\t<p>The primary afferent axons are nerve fibers connected to different types of receptors around the body. There are various sizes of primary afferent axons. They are drawn to scale, but they are shown 2000 times larger than life size. The diameter of an axon is correlated with its conduction velocity and with the type of sensory receptor to which it is connected. \u00a0<\/p>\n<p>The different nerve\u00a0fiber\u00a0groups are\u00a0<b><i>A-alpha, A-beta, A-delta and C-nerve fibers<\/i><\/b>.\u00a0\u00a0<\/p>\n<p>A-alpha, A-beta and A-delta nerve fibers are insulated with myelin. C-nerve fibers are unmyelinated. It is believed the thicker a nerve fiber the faster information travels. Vice versa, the thinner a nerve fiber, the slower information travels.\u00a0<\/p>\n<h3>\n\t\tSegmental and Longitudinal Organisation \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Segmental-and-Longitudinal-Org.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.11 \" itemprop=\"image\" height=\"546\" width=\"465\" title=\"Segmental and Longitudinal Org\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.11 \n\t<p>The spinal cord is divided into four different regions: the cervical, thoracic, lumbar and sacral regions. Each spinal nerve, consisting of dorsal root and ventral root axons, passes through a notch between the vertebrae (the &#8220;back bones&#8221;) of the spinal column. <\/p>\n<p>The 30 spinal segments are divided into 4 groups. Each segment is named after the vertebra\u00a0adjacent to\u00a0where the nerves originate: cervical (C) 1-8, thoracic (T) 1-12, lumbar (L) 1-5, and sacral (S) 1-5.\u00a0\u00a0<\/p>\n<p>Dorsal and ventral roots enter and leave the vertebral column through intervertebral foramen at the vertebral segments corresponding to the spinal segment. The arrangement of paired dorsal and ventral roots is repeated\u00a0<b>30 times <\/b>down the length of the human spinal cord.\u202f\u00a0<\/p>\n<h3>\n\t\tDermatomes \n\t<\/h3>\n<h4>\n\t\tVideo 13: Dermatomes\n\t<\/h4>\n\t<p>A\u202fdermatome\u202fis the area of skin triggered by right and left dorsal roots of a spinal segment. If a nerve is cut, one loses sensation from that dermatome.\u00a0<\/p>\n<p>Watch the video below for more information.\u00a0\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/l-_FLH78UvY\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.11<\/p>\n<h3>\n\t\tThe Dorsal Column-Medical Leminiscal Pathway\n\t<\/h3>\n<h4>\n\t\tVideo 14: The Dorsal Column-Medical Leminiscal Pathway\n\t<\/h4>\n\t<p>The dorsal column-medial lemniscal pathway is\u202fthe major route by which touch and proprioceptive information ascend to the cerebral cortex.\u00a0<\/p>\n<p>Watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/The-Dorsal-Column-Medical-Leminiscal-Pathway-.png\" alt=\"\"\/>\n\t<p>Reference: (1) Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.15; (2) Krebs et al., Lippincott&#8217;s Illustrated<\/p>\n<p>Reviews: Neuroscience, Figure 13.9; (3) Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.18\u00a0<\/p>\n<h2>\n\t\t3.5. Somatosensory Cortex and Plasticity\n\t<\/h2>\n<h3>\n\t\tSomatosensory Cortex \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Somatosensory-Cortex.png\" alt=\"Reference: Krebs et al., Lippincott's Illustrated Reviews: Neuroscience, Figure 13.9 \" itemprop=\"image\" height=\"401\" width=\"707\" title=\"Somatosensory Cortex\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 13.9 \n\t<p>The somatosensory cortex is the part of the brain that recognizes where ascending sensory tracts originate. Each sensory tract has a corresponding region of the cortex, so that all sensory pathways for the left hand\u00a0terminate in one area, all pathways for the left foot terminate\u00a0in another area, and so on. Within the cortical region for a particular body part, columns of neurons are devoted to\u00a0particular types of receptors. For example, a cortical column activated by cold receptors in the left hand may be found next to a column activated by pressure receptors in the skin of the left hand. This columnar arrangement creates a highly organized structure that maintains\u00a0the association between specific receptors and the sensory modality they\u00a0transmit.\u00a0<\/p>\n<h3>\n\t\tHomunculus\n\t<\/h3>\n<h4>\n\t\tVideo 15: Homunculus &#8211; The Little man in the Brain\n\t<\/h4>\n\t<p>Watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/fbvExi69aX0\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t\t<h3>\n\t\tSomatotopic Map Plasticity\u202f\n\t<\/h3>\n\t<p><em>The Cortical Representation of the Human Hand Area Can Be Modified<\/em><\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Somatotopic-Map-Plasticity-.png\" alt=\"A. Location of The Left Hand Map on Right Hemisphere of Monkey Brain \" itemprop=\"image\" height=\"717\" width=\"715\" title=\"Somatotopic Map Plasticity\u202f\" onerror=\"this.style.display='none'\"  \/>\n\t\tA. Location of The Left Hand Map on Right Hemisphere of Monkey Brain \n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Normal-Hand-Palmer-Surface.png\" alt=\"B. Normal hand, Palmar Surface \" itemprop=\"image\" height=\"411\" width=\"523\" title=\"Normal Hand Palmer Surface\" onerror=\"this.style.display='none'\"  \/>\n\t\tB. Normal hand, Palmar Surface \n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Surgical-removal-of-third-finger.png\" alt=\"C. Reorganisation of Cortical Map after Surgical Removal of Third Finger (D3) \" itemprop=\"image\" height=\"262\" width=\"562\" title=\"Surgical removal of third finger\" onerror=\"this.style.display='none'\"  \/>\n\t\tC. Reorganisation of Cortical Map after Surgical Removal of Third Finger (D3) \n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Training-of-Two-Fingertips.png\" alt=\"D. Reorganisation of Cortical Map after Discrimination Training of Two Fingertips \" itemprop=\"image\" height=\"251\" width=\"526\" title=\"Training of Two Fingertips\" onerror=\"this.style.display='none'\"  \/>\n\tD. Reorganisation of Cortical Map after Discrimination Training of Two Fingertips<br \/>\nReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.23\u00a0\n\t<p><strong><i>Does reorganisation of afferent fibers also occur in the human brain? <\/i>\u00a0<\/strong><\/p>\n<p>Magnetoencephalography can now be used to construct functional maps of the hand in normal subjects with a precision of millimeters. This imaging technique has been used to compare the hand area in the cortex of normal adult humans to that of patients with a congenital fusion of the fingers (syndactyly). Patients with this syndrome do not have individual fingers-their hand is much like a fist-so that neural activity in one part of the hand is always correlated with activity in all other parts of the hand. The size of the representation in the cortex of the syndactylic hand is considerably less than that of a normal person, and within this shrunken representation the fingers are not organized somatotopically, as are separate fingers.<\/p>\n<p>In contrast, if a person loses a finger or limb, the\u00a0portion\u00a0of the somatosensory cortex devoted to the missing structure begins to be taken over by sensory fields of adjacent structures. Reorganization of the somatosensory cortex map is an example of the remarkable plasticity of the brain. Unfortunately, sometimes the reorganization is not perfect and can result in sensory sensations, including pain, that the brain interprets as\u00a0being located in\u00a0the missing limb (phantom limb pain).\u202f\u00a0<\/p>\n<h3>\n\t\tPhantom Limb Sensations\n\t<\/h3>\n\t<p>Phantom limb sensations can be evoked by touching the face. A common experience among amputees is the perception of sensations coming from the missing limb when other body parts are touched.\u202f\u00a0<\/p>\n\t<ol>\n<li>\n<ol>\n<li aria-setsize=\"-1\" data-leveltext=\"%1.\" data-font=\"\" data-listid=\"1\" data-list-defn-props=\"{&quot;335552541&quot;:0,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769242&quot;:[65533,0],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;%1.&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">A subject whose arm was amputated above the left elbow shows sites on his face where stimulation (brushing the face with a cotton swab) elicits sensation referred to the phantom digits. Regions of the body that evoke referred sensations are called reference fields. Stimulation of the region\u00a0labeled\u00a0T always evoked sensations in the phantom thumb. Stimulation of facial areas marked I, P, and B evoked sensation in the phantom index finger, pinkie, and ball of the thumb, respectively. This patient was tested four weeks after amputation.<\/li>\n<li aria-setsize=\"-1\" data-leveltext=\"%1.\" data-font=\"\" data-listid=\"1\" data-list-defn-props=\"{&quot;335552541&quot;:0,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769242&quot;:[65533,0],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;%1.&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">The upper arm of a subject who experienced referred sensation in the face and in two distinct areas on the arm-one area close to the line of amputation and a second area 6 cm above the elbow crease. Each area is a precise spatial map of the lost digits; the maps are almost identical except for the absence of fingertips in the upper map. When the patient imagined pronating his phantom lower arm, the entire upper map shifted in the same direction by about 1.5 cm. Stimulating the skin region between these two maps did not elicit sensations in the phantom limb.<\/li>\n<li aria-setsize=\"-1\" data-leveltext=\"%1.\" data-font=\"\" data-listid=\"1\" data-list-defn-props=\"{&quot;335552541&quot;:0,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769242&quot;:[65533,0],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;%1.&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">Portion of sensory homunculus showing how the cortical area receiving inputs from the hand is flanked by the regions devoted to the face and the arm. Rearrangement of these cortical inputs is thought to be responsible for some types of phantom limb sensation.\u00a0<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<h2>\n\t\t3.6. Summary:  Somatosensory System &#8211; Touch\n\t<\/h2>\n1\nSomatosensory receptors distributes throughout the body and can sense multiple sensations including touch, temperature, and pain (nociception).\n2\nSkin is our largest sensory organs and contains at least 5 different mechanoreceptors. Temperature receptor sense heat and cold.\n3\nA single sensory receptor can encode stimulus features such as intensity, duration, position, and sometimes directions.\n4\nIn addition, sensory receptor can adapt to the stimulus and detect vibrations.\n5\nThere are two main anatomical pathways: dorsal column-medial lemniscal pathway and the trigeminal touch pathway, to send the sensory signal through thalamus to the cortex.\n6\nSomatic sensory and motor projections from and to the body surface and muscle are arranged in an orderly way in the cortex. This somatosensory map can be modified (known as plasticity).\n<h2>\n\t\t3.7. Further Readings\n\t<\/h2>\n\t<ol>\n<li>\n<ol>\n<li>Bears et al., Neuroscience: exploring the brain, 4th edition, chapter 8, 11 and 12<\/li>\n<li>Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, chapter 22<\/li>\n<li>Silverthorn, Human Physiology, 5th edition, chapter 10<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n<h1>\n\t\tChapter 4: Physiological and Patho-Physiological Basis of Pain\n\t<\/h1>\n<h2>\n\t\tIntroduction\n\t<\/h2>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/4-Introduction.png\" alt=\"#4 Introduction\" itemprop=\"image\" height=\"692\" width=\"1050\" title=\"#4 Introduction\" onerror=\"this.style.display='none'\"  \/>\n\t<p><em>Have you felt &#8220;in pain&#8221;? <\/em><\/p>\n<p><em>How does the brain process this sensation? <\/em><\/p>\n<p><em>Was there an instance when your pain was alleviated by something? <\/em><\/p>\n<p><em>How do analgesics work?\u00a0<\/em><\/p>\n<h2>\n\t\tOverview\n\t<\/h2>\n\tIn this chapter, we will take a look at the physiology and patho-physiology of pain.\n\n<b>Learning Objectives<\/b>\n\tAt the end of this chapter, you should be able to:\n\n1\nExplain what nociceptors are and the transduction of painful stimuli\n2\nDescribe the primary afferent and spinal mechanisms\n3\nDifferentiate between ascending pain pathways (spinothalamic tract), which are Lateral sensory-discriminative pathway and Medial affective-motivational pathway\n4\nDiscuss the regulation of pain\n<h2>\n\t\t4.1. Nociceptors and the Transduction of Painful Stimuli\n\t<\/h2>\n<h3>\n\t\tNociceptors initiate protective responses\n\t<\/h3>\n\t<p>Nociceptors, which came from the word &#8220;nocere&#8221;, &#8220;to injure&#8221;, are receptors that respond to a variety of strong noxious stimuli (chemical, mechanical, or thermal) that cause or have the potential to cause tissue damage.<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Nociceptors-initiate-protective-responses.png\" alt=\"Activation of nociceptors initiates adaptive, protective responses, such  as the reflexive withdrawal of a hand from a hot stove touched  accidentally.  \" itemprop=\"image\" height=\"517\" width=\"780\" title=\"Nociceptors initiate protective responses\" onerror=\"this.style.display='none'\"  \/>\n\t\tActivation of nociceptors initiates adaptive, protective responses, such  as the reflexive withdrawal of a hand from a hot stove touched  accidentally.  \n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Nociceptors-initiate-protective-responses.-2.png\" alt=\"Nociceptors are not limited to the skin. Discomfort from overuse of muscles and joints helps us avoid additional damage to these structures.  \" itemprop=\"image\" height=\"520\" width=\"787\" title=\"Nociceptors initiate protective responses. 2\" onerror=\"this.style.display='none'\"  \/>\n\t\tNociceptors are not limited to the skin. Discomfort from overuse of muscles and joints helps us avoid additional damage to these structures.  \n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Nociceptors-initiate-protective-responses-3.png\" alt=\"Two sensations may be perceived when nociceptors are activated: pain and itch.  \" itemprop=\"image\" height=\"517\" width=\"777\" title=\"Nociceptors initiate protective responses 3\" onerror=\"this.style.display='none'\"  \/>\n\t\tTwo sensations may be perceived when nociceptors are activated: pain and itch.  \n\t<p>Nociceptors are sometimes called pain receptors, even though pain is a perceived sensation rather than a stimulus.\u00a0\u00a0<\/p>\n<p>Nociceptive pain is mediated by free nerve endings whose ion channels are sensitive to a variety of chemical, mechanical, and thermal stimuli. For example, the membrane channels called vanilloid receptors (also called transient receptor potential V1 or TRPV1 channels) respond to\u00a0damaging heat from a stove or other source, as well as to capsaicin, the chemical that makes hot chili peppers burn your mouth.\u00a0\u00a0<\/p>\n<p>At the opposite end of the temperature spectrum, researchers recently\u00a0identified\u00a0a membrane protein that responds both to cold and to menthol, one reason mint-flavored\u00a0foods feel cool. Pain can be felt in skeletal muscles (deep somatic pain) as well as in the skin.\u00a0\u00a0<\/p>\n<p>Muscle pain during exercise is associated with the onset of anaerobic metabolism and is often perceived as a burning sensation in the muscle (as in go for the burn!). Some investigators have suggested that the exercise-induced metabolite responsible for the burning sensation is K*, known to enhance the pain response. Muscle pain from ischemia (lack of adequate blood ow that reduces oxygen supply) also occurs during myocardial infarction (heart attack). \u00a0<\/p>\n<h4>\n\t\tVideo 16: Nociceptive Fibers\n\t<\/h4>\n\t<p>Nociceptors can be activated by extreme temperature, intense mechanical stimulation, or an array of chemicals through specific receptors.\u00a0\u00a0<\/p>\n<p>Watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/a4HdZknK8PQ\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: (1) Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.1; (2) Bears et al., Neuroscience: exploring the brain, 4th edition,<\/p>\n<p>Figure 12.25; (3) Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.27\u00a0<\/p>\n<h2>\n\t\t4.2. Referred Pain: Viscerosomatic Convergence\n\t<\/h2>\n<h3>\n\t\tNociceptor axons from the viscera enter the spinal cord by the same route as the cutaneous nociceptors.\n\t<\/h3>\n\t<p>Within the spinal cord, there is a substantial mixing of information from these two sources of input. This\u00a0cross-talk gives rise to the phenomenon of referred pain, where visceral nociceptor activation is perceived as a cutaneous sensation.<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Nociceptor-axons-from-the-viscera-.png\" alt=\"Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.29 \" itemprop=\"image\" height=\"567\" width=\"882\" title=\"Nociceptor axons from the viscera\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.29 \n\t<p>Pain in the heart and other internal organs (visceral pain) is often poorly localized and may be felt in areas far removed from the site of the stimulus.\u00a0\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/multiple-primary-sensory-neurons.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.11 \" itemprop=\"image\" height=\"396\" width=\"503\" title=\"multiple primary sensory neurons\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.11 \n\t<p>For example, the pain of cardiac ischemia may be felt in the neck\u00a0and down\u00a0the left shoulder and arm. This referred pain\u00a0apparently occurs\u00a0because multiple primary sensory neurons converge on a single ascending tract.\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/visceral-receptors.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.11 \" itemprop=\"image\" height=\"355\" width=\"502\" title=\"visceral receptors\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.11 \n\t<p>According to this model, when painful stimuli arise in visceral receptors, the brain is unable to distinguish visceral signals from the more common signals arising from somatic receptors. As a result, it interprets the pain as coming from the somatic regions rather than the viscera.\u00a0\u00a0<\/p>\n<h2>\n\t\t4.3. Sensitisation of Peripheral Receptors\n\t<\/h2>\n<h3>\n\t\tTissue damage and inflammation result in the release of inflammatory molecules, such as bradykinin and prostaglandins, which sensitise peripheral nociceptors.  \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Tissue-damage-and-inflammation-resul.png\" alt=\"Reference: Krebs et al., Lippincott's Illustrated Reviews: Neuroscience, Figure 22.2 \" itemprop=\"image\" height=\"376\" width=\"787\" title=\"Tissue damage and inflammation resul\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.2 \n\t<p>In addition, when a noxious stimulus is detected by a nociceptor, free nerve endings will release substance P and CGRP. These two neuropeptides contribute to the inflammatory response at the site of tissue injury by stimulating mast cell release of histamine and bradykinin. CGRP induces vasodilation, which results in further release of inflammatory molecules.\u00a0<\/p>\n<p>Nociceptor activation is modulated by local chemicals that are released upon tissue injury, including K*, histamine, and prostaglandins released from damaged cells; serotonin released from platelets activated by tissue damage; and the peptide substance P, which is secreted by primary sensory neurons. \u00a0<\/p>\n<p>These chemicals, which also mediate the inflammatory response at the site of injury, either activate nociceptors or sensitize them by lowering their activation threshold. Increased sensitivity to pain at sites of tissue damage is called in inflammatory pain.\u00a0<\/p>\n<h3>\n\t\tNociceptors may activate two pathways\n\t<\/h3>\n\t<ol>\n<li> Reflexive protective responses that are integrated at the level of the spinal cord<\/li>\n<li> Ascending pathways to the cerebral cortex that become conscious sensation (pain or itch)<\/li>\n<\/ol>\n<p>Primary sensory neurons from nociceptors terminate in the dorsal horn of the spinal cord. There they synapse onto secondary sensory neurons that project to the brain or onto interneurons for local circuits.\u00a0<\/p>\n<h2>\n\t\t4.4. Projection of Fibers into the Spinal Cord\n\t<\/h2>\n<h3>\n\t\tThe synaptic targets of Ad and C fibers are either nociceptive-specific (NS) cells, which synapse only with Ad and C fibers, or wide dynamic range (WDR) neurons, which receive synaptic input from all types of sensory fibers.  \n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/synaptic-targets-of-Ad-and-C-fibers.png\" alt=\"Reference: Krebs et al., Lippincott's Illustrated Reviews: Neuroscience, Figure 22.3 \" itemprop=\"image\" height=\"413\" width=\"786\" title=\"synaptic targets of Ad and C fibers\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.3 \n\t<p>Whereas NS neurons will encode only for painful stimuli and project to higher\u00a0centers, the WDR cells can encode for a range of stimuli, both painful and non-painful.\u00a0\u00a0<\/p>\n<p><b>Neurotransmitter<\/b>\u00a0<\/p>\n<p>The synapse in the posterior horn is excitatory. The neurotrasmitters released by the afferent nociceptive fibers are glutamate, which acts mainly on a-amino-3-hydroxy-5-methyl-4-isoxazaole propionic acid (AMPA) and N-methyl-d-aspartic acid (NMDA) receptors; substance P, which acts on the NK1 receptor, and GRP, which also has an excitatory effect via the CGRP receptor. \u00a0<\/p>\n<p><b>Wide Dynamic Range Neurons<\/b>\u00a0<\/p>\n<p>WDR cells can fire Aps in a graded fashion, depending on the stimulus intensity. Stimulus intensity is encoded by the frequency of C-fiber signaling: the more painful the stimulus, the higher the frequency of C-fiber discharge and the greater the WDR neuron response. The WDR neuron can then amplify this signal through a mechanism called &#8220;wind-up&#8221;.<\/p>\n<h4>\n\t\tVideo 17: Projection of Fibers into the Spinal Cord\n\t<\/h4>\n\t<p>Watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/iF6LspA2_fo\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.3\u00a0<\/p>\n<h2>\n\t\t4.5. Principles of Central Sensitisation &#8220;Wind-up&#8221;\n\t<\/h2>\n<h3>\n\t\tWind-up: Central sensitization, or &#8220;wind-up,&#8221; in the spinal cord is mediated through neurotransmitter release at the postsynaptic neuron in the posterior horn.\n\t<\/h3>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Central-sensitization.png\" alt=\"Reference: Krebs et al., Lippincott's Illustrated Reviews: Neuroscience, Figure 22.4 \" itemprop=\"image\" height=\"331\" width=\"788\" title=\"Central sensitization\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.4 \n\t<p><strong>Wind-up:\u00a0<\/strong><\/p>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"2\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">is\u00a0essentially an\u00a0amplification system within the spinal cord to respond to the cumulative nociceptive input from C\u00a0fibers.\u00a0\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"2\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"2\" data-aria-level=\"1\">results from the repetitive excitatory stimulation of the WDR neuron through glutamate acting\u00a0mainly on\u00a0AMPA receptors.\u00a0\u00a0<\/li>\n<\/ul>\n<p>This increased AP frequency and sustained membrane depolarization result in activation of NMDA receptors. The NMDA receptor is usually inactive due to blockade of channels by Mg2+ ions. Sustained depolarization releases this Mg2+ block, and the NMDA receptor can then be activated by glutamate. Significantly, because the NMDA receptor is Ca2+ permeable, Ca2+ influx into the cell changes the electrophysiological\u00a0signaling\u00a0properties of the WDR neuron.\u00a0\u00a0<\/p>\n<h2>\n\t\t4.6. Hyperalgesia and Allodynia\n\t<\/h2>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Hyperalgesia<\/h5>\n\t\t\t<p>When the response to a normally painful stimulus is heightened (more pain felt than the usual).<\/p>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Allodynia<\/h5>\n\t\t\t<p>When a normally nonpainful stimulus is perceived as painful (for example, light touch on sunburn).<\/p>\n<h2>\n\t\t4.7. Ascending Pain Pathways\n\t<\/h2>\n<h3>\n\t\tNociceptors may activate two pathways\n\t<\/h3>\n\t<p>Reflexive protective responses that are integrated at the level of the spinal cord, with ascending pathways to the cerebral cortex that become conscious sensation (pain or itch). \u00a0<\/p>\n<h4>\n\t\tVideo 18: Ascending Pain Pathways\n\t<\/h4>\n\t<p>Watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/5MFnU73dZic\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.30 &amp; 12.31\u00a0<\/p>\n<h2>\n\t\t4.8. Medial Affective-Motivational Pathway vs Lateral Sensory-Discriminative Pathway\n\t<\/h2>\n\t<p><b>Medial Affective-Motivational Pathways<\/b>\u00a0<\/p>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"3\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">These pathways influence the emotional and visceral responses to pain as well as the descending modulation of pain.\u00a0\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"3\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"2\" data-aria-level=\"1\">The medial affective-motivational component of the system is the &#8220;second&#8221; pain, the dull, throbbing poorly localised type of pain. \u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"3\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"3\" data-aria-level=\"1\">This\u00a0component\u00a0includes the emotional response to pain:\u00a0&#8220;Ouch!! That hurts-I\u00a0don&#8217;t\u00a0like it!&#8221;\u00a0<\/li>\n<\/ul>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Medial-Affective-Motivational-Pathways-.png\" alt=\"Reference: Krebs et al., Lippincott's Illustrated Reviews: Neuroscience, Figure 22.5 \" itemprop=\"image\" height=\"898\" width=\"462\" title=\"Medial Affective-Motivational Pathways\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.5 \n\t<p><b>Lateral Sensory-Discriminative Pathway<\/b>\u00a0<\/p>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"4\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\">The tract is organized\u00a0somatotopically\u00a0and allows for the localization of pain in the primary somatosensory cortex.\u00a0\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"4\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"2\" data-aria-level=\"1\">The lateral sensory-discriminative pathway mediates the\u00a0&#8220;first&#8221;\u00a0pain, the sharp, well-localized sensation relayed rapidly to the cortex.\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"4\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"3\" data-aria-level=\"1\">&#8220;I have a sharp pain in my left arm!&#8221;\u00a0<\/li>\n<\/ul>\n<h4>\n\t\tVideo 19: Medial System vs Lateral System\n\t<\/h4>\n\t<p>The ascending pathways for nociception cross the body&#8217;s midline in the spinal cord and ascend to the thalamus and sensory areas of the cortex. The pathways also send branches to the limbic system and hypothalamus. As a result, pain may be accompanied by emotional distress (suffering) and a variety of autonomic reactions, such as nausea, vomiting, or sweating. \u00a0<\/p>\n<p>Watch the video below for more information.\u00a0<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/ZR4JyXzLuj4\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.5\u00a0<\/p>\n<h2>\n\t\t4.9. Gate Control Model of Pain Modulation\n\t<\/h2>\n<h3>\n\t\tNonpainful stimuli can diminish the pain signal\n\t<\/h3>\n\t<p>Pain can also be suppressed in the dorsal horn of the spinal\u00a0cord, before the stimuli are sent to ascending spinal tracts. Normally, tonically active inhibitory interneurons in the spinal cord inhibit ascending pathways for pain.<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Nonpainful-stimuli-can-diminish-the-pain-signal.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.12 \" itemprop=\"image\" height=\"380\" width=\"465\" title=\"Nonpainful stimuli can diminish the pain signal\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.12 \n\t<p>C\u00a0fibers\u00a0from nociceptors synapse on these inhibitory interneurons. When activated by a painful stimulus, the C\u00a0fibers\u00a0simultaneously excite the ascending path and block the tonic inhibition. This action allows the pain signal from the C\u00a0fiber\u00a0to travel unimpeded to the brain.\u00a0\u00a0<\/p>\n\t\t\t\t<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/A-beta-fibers-.png\" alt=\"Reference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.12 \" itemprop=\"image\" height=\"497\" width=\"457\" title=\"A-beta fibers\" onerror=\"this.style.display='none'\"  \/>\n\t\tReference: Silverthorn, Human Physiology, 5th edition, Chapter 10, Figure 10.12 \n\t<p>In the gate control theory of pain modulation, A-beta fibers carrying sensory information about mechanical stimuli help block pain transmission. The A-beta fibers synapse on the inhibitory interneurons and enhance the interneuron&#8217;s inhibitory activity. If simultaneous stimuli reach the inhibitory neuron from the A-beta and C fibers, the integrated response is partial inhibition of the ascending pain pathway so that pain perceived by the brain is lessened.\u00a0<\/p>\n<p>The gate control theory explains why rubbing a bumped elbow or shin lessens your pain: the tactile stimulus of rubbing activates A-beta fibers and helps decrease the sensation of pain. \u00a0<\/p>\n<h2>\n\t\t4.10. Conceptual Overview of Pain Modulation Network\n\t<\/h2>\n<h3>\n\t\tDescending influences come from the brain stem\n\t<\/h3>\n\t<p>Other modulatory systems come from\u00a0a number of\u00a0areas in the brainstem, which receive input from the ascending nociceptive pathways.\u00a0<\/p>\n<h4>\n\t\tVideo 20: Conceptual Overview of Pain Modulation Network\n\t<\/h4>\n\t<p>Watch the video below for more information<\/p>\n\t\t\t\t\t<img decoding=\"async\" src=\"https:\/\/i.ytimg.com\/vi\/AmJjejaaTFc\/maxresdefault.jpg\" alt=\"youtube-video-thumbnail\"\/>\n\t<p>Reference: (1) Bears et al., Neuroscience: exploring the brain, 4th edition, Figure 12.34; (2) Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, Figure 22.8\u00a0<\/p>\n<h2>\n\t\t4.11. Endogenous Opioid System\n\t<\/h2>\n<h4>\n\t\tVideo 5: Labeled Lines\n\t<\/h4>\n\t<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"5\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"1\" data-aria-level=\"1\"><b>Endogenous opioid system\u00a0<\/b>provides modulatory influence on cortical pain process.\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"5\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"2\" data-aria-level=\"1\">Opioid receptors can be found at all levels of the pain system. Opioid receptors are physiologically activated by a group of endogenous molecules that comprise <b>enkephalins<\/b>, <b>endorphins<\/b>, and <b>dynorphins<\/b>. These opioid peptides act as neurotransmitters or neuromodulators and can produce potent <b>analgesic <\/b>effects.\u00a0\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"5\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"3\" data-aria-level=\"1\">Activation of opioid receptors results in the inhibition of voltage-gated Ca2+ channels and\/or the opening of K+ channels, which results in <b>hyperpolarization and less neuronal excitability<\/b>.\u00a0\u00a0<\/li>\n<\/ul>\n<ul>\n<li aria-setsize=\"-1\" data-leveltext=\"\u2022\" data-font=\"Calibri\" data-listid=\"5\" data-list-defn-props=\"{&quot;335552541&quot;:1,&quot;335559685&quot;:720,&quot;335559991&quot;:360,&quot;469769226&quot;:&quot;Calibri&quot;,&quot;469769242&quot;:[8226],&quot;469777803&quot;:&quot;left&quot;,&quot;469777804&quot;:&quot;\u2022&quot;,&quot;469777815&quot;:&quot;hybridMultilevel&quot;}\" data-aria-posinset=\"4\" data-aria-level=\"1\"><b>Placebo\u00a0<\/b>effect\u00a0<\/li>\n<\/ul>\n<h2>\n\t\t4.12. Four Main Types of Pain\n\t<\/h2>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Radicular Pain <\/h5>\n\t\t\t<p><img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Radicular-Pain.png\" alt=\"Radicular Pain\" \/><\/p>\n<p>Pain distributed over an area that is consistent with the boundaries of a dermatome.<\/p>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Referred Pain<\/h5>\n\t\t\t<p><img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Referred-Pain.png\" alt=\"Radicular Pain\" \/><\/p>\n<p>Pain that is perceived in a surface area of the body far removed from its actual source.<\/p>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Phantom Pain<\/h5>\n\t\t\t<p><img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Phantom-Pain.png\" alt=\"Phantom Pain\" \/><\/p>\n<p>Pain that is felt in a part of the body that either no longer exists because of amputation or is insensate caused by nerve severance.<\/p>\n\t\t\t\t\t\t<h5 tabindex=\"0\">Central Pain<\/h5>\n\t\t\t<p><img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/uploads\/sites\/44\/2025\/11\/Central-Pain-.png\" alt=\"Elderly woman in hospital bed, receiving neurological care.\"  >   <\/p>\n<p>Pain arises from a lesion in the thalamus or cortex that is interpreted as pain in the body part corresponding to the lesion.<\/p>\n<h2>\n\t\t4.13. Summary: Pain\n\t<\/h2>\n1\nNociceptors are present in most body tissues, including skin, bone, muscle, most internal organs, blood vessels, and the heart. They are notably absent in the brain itself, except for the meninges.\n2\nThe majority of nociceptors respond to mechanical, thermal and chemical stimuli and the therefore called polymodal nociceptors.\n3\nNoxious stimuli are transduced into electrical activity at the peripheral terminals of unmyelinated C-fiber and thinly myelinated Ad-fiber nociceptors by specific receptors or ion channels sensitive to heat, mechanical stimuli, protons and cold. This activity is conducted to the spinal cord and after transmission in the central pathways, to the cortex, where the sensation of pain is experienced.\n4\nReferred Pain\n5\nComparison of somatosensory and pain pathways\n<h2>\n\t\t4.14. Further Readings\n\t<\/h2>\n\t<ol>\n<li>\n<ol>\n<li>Bears et al., Neuroscience: exploring the brain, 4th edition, chapter 8, 11 and 12<\/li>\n<li>Krebs et al., Lippincott&#8217;s Illustrated Reviews: Neuroscience, chapter 22<\/li>\n<li>Silverthorn, Human Physiology, 5th edition, chapter 10<\/li>\n<\/ol>\n<\/li>\n<\/ol>\n\t\t\t\t<img decoding=\"async\" src=\"https:\/\/medicine.nus.edu.sg\/medixperience\/wp-content\/plugins\/bb-plugin\/img\/pixel.png\" alt=\"\" itemprop=\"image\" onerror=\"this.style.display='none'\"  \/>\n\n","protected":false},"excerpt":{"rendered":"<p>Explore the nervous system with our neurobiology e-book, covering neural mechanisms, networks, and disorders.<\/p>\n","protected":false},"featured_media":472,"parent":0,"menu_order":0,"template":"","meta":{"_acf_changed":false,"site-sidebar-layout":"no-sidebar","site-content-layout":"page-builder","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"disabled","ast-breadcrumbs-content":"","ast-featured-img":"disabled","footer-sml-layout":"","theme-transparent-header-meta":"default","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"set","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"var(--ast-global-color-4)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}}},"learning-resources-categories":[121,32],"domain":[112],"occupation":[22],"speciality":[79],"class_list":["post-471","learning-resource","type-learning-resource","status-publish","has-post-thumbnail","hentry","learning-resources-categories-blog-page","learning-resources-categories-e-books","domain-basic-science","occupation-undergraduate-student","speciality-neurology"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.4 - 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