Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Neuroscience: Exploring the Brain, 3e Chapter 12: The Somatic Sensory System
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Introduction Somatic Sensation –Enables body to feel, ache, chill –Responsible for touch and pain –Somatic sensory system: Different from other systems Receptors: Broadly distributed Responds to many kinds of stimuli
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Types and layers of skin –Hairy and glabrous (hairless - e.g., palms) –Epidermis (outer) and dermis (inner) Functions of skin –Protective –Prevents evaporation of body fluids –Provides direct contact with world Mechanoreceptors –Most somatosensory receptors are mechanoreceptors
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Mechanoreceptors (Cont’d) –Pacinian corpuscles –Ruffini's endings –Meissner's corpuscles –Merkel's disks –Krause end bulbs
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Mechanoreceptors (Cont’d) –Small and large receptive fields
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Mechanoreceptors (Cont’d) –Receptors - receptive field size and adaptation rate
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Mechanoreceptors (Cont’d) –Two-point discrimination Receptive field density Receptive field size Computing power Special neural mechanisms
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Primary Afferent Axons –AC –C fibers mediate pain and temperature –Amediates touch sensations mediates acute, early pain
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch The Spinal cord –Spinal segments (30)- spinal nerves within 4 divisions of spinal cord.
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Spinal cord (Cont’d) –Divisions of spinal gray matter: Dorsal horn; Intermediate zone; Ventral horn Myelinated A axons (touch-sensitive)
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Dorsal Column–Medial Lemniscal Pathway –Touch and proprioception
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch The Trigeminal Touch Pathway –Somatosensory information from face
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Somatosensory Cortex –S1 = Area 3b –Adjacent areas: Postcentral gyrus: 3a,1,2, Posterior Parietal Cortex: 5,7
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Somatosensory Cortex –Cortical Somatotopy: Homunculus
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Somatosensory Cortex (Cont’d) –S1: Rat“Barrel cortex” (vibrissae)
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Somatosensory Cortex (Cont’d) –3b and 1 – Two mirror image maps - Owl monkey
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch Somatosensory Cortex (Cont’d) –Cortical Map Plasticity –Remove digits or overstimulate – examine somatotopy before and after –Maps are dynamic
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins
Touch Somatosensory Cortex (Cont’d) –The Posterior Parietal Cortex Involved in somatic sensation, visual stimuli, and movement planning Agnosia Astereoagnosia Neglect syndrome
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Nociceptors Pain and nociception –Pain - feeling of sore, aching, throbbing –Nociception - sensory process, provides signals that trigger pain Nociceptors: Transduction of Pain –Mechanically gated ion channels opened by: Strong mechanical stimulation, temperature extremes, oxygen deprivation, chemicals –Damaged cells release substances that open ion channels Proteases (-> bradykinin), STP, K+ ion channels Histamine
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Nociception and the Transduction of Painful Stimuli (Cont’d) –Types of Nociceptors Polymodal Mechanical Thermal –Hyperalgeia Primary and secondary
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Primary Afferents and Spinal mechanisms –First pain and second pain –Referred pain: Angina
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Ascending Pain Pathways
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Ascending Pain Pathways –Touch and pain systems segregated Nerve endings in the skin Diameter of axons Connections in spinal cord Touch – Ascends Ipsilaterally Pain – Ascends Contralaterally –Brown-Séquard Syndrome –Trigeminal Pain Pathway
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Ascending Pain Pathways (Cont’d)
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Pain Regulation –Afferent Regulation –Gate theory of pain - Melzack and Wall
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Pain Pain Regulation –Descending Regulation -> –The endogenous opiates Opioids and endomorphins
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Temperature Thermoreceptors –“Hot” and “cold” receptors –Varying sensitivities
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Temperature Thermoreceptors –Hot and cold receptors
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Temperature The Temperature Pathway –Organization of temperature pathway Identical to pain pathway –Cold receptors coupled to A and C –Hot receptors coupled to C
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Concluding Remarks Sensory systems exhibit similar organization and function Somatic sensory information segregated within the spinal cord and cerebral cortex – Parallel processing of information Perception of object involves the seamless coordination of somatic sensory information
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins End of Presentation
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins Touch The Spinal cord –Dermatomes- 1-to-1 correspondence with segments –Shingles
Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins