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Neuroscience: Exploring the Brain, 3e

Neuroscience: Exploring the Brain, 3e. Chapter 12: The Somatic Sensory System. Introduction. Somatic Sensation Enables body to feel, ache, chill Responsible for touch and pain Somatic sensory system: Different from other systems Receptors: Broadly distributed

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Neuroscience: Exploring the Brain, 3e

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  1. Neuroscience: Exploring the Brain, 3e Chapter 12: The Somatic Sensory System

  2. 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

  3. 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

  4. Touch • Mechanoreceptors (Cont’d) • Pacinian corpuscles • Ruffini's endings • Meissner's corpuscles • Merkel's disks • Krause end bulbs

  5. Touch • Mechanoreceptors (Cont’d) • Small and large receptive fields

  6. Touch • Mechanoreceptors (Cont’d) • Receptors - receptive field size and adaptation rate

  7. Touch • Mechanoreceptors (Cont’d) • Two-point discrimination • Receptive field density • Receptive field size • Computing power • Special neural mechanisms

  8. Touch • Primary Afferent Axons • Aa, Ab, Ad, C • C fibers mediate pain and temperature • Abmediates touch sensations - Ad mediates acute, early pain

  9. Touch • The Spinal cord • Spinal segments (30)- spinal nerves within 4 divisions of spinal cord.

  10. Touch • Spinal cord (Cont’d) • Divisions of spinal gray matter: Dorsal horn; Intermediate zone; Ventral horn • Myelinated Ab axons (touch-sensitive)

  11. Touch • Dorsal Column–Medial Lemniscal Pathway • Touch and proprioception

  12. Touch • The Trigeminal Touch Pathway • Somatosensory information from face

  13. Touch • Somatosensory Cortex • S1 = Area 3b • Adjacent areas: • Postcentral gyrus: 3a,1,2, • Posterior Parietal Cortex: 5,7

  14. Touch • Somatosensory Cortex • Cortical Somatotopy: Homunculus

  15. Touch • Somatosensory Cortex (Cont’d) • S1: Rat“Barrel cortex” (vibrissae)

  16. Touch • Somatosensory Cortex (Cont’d) • 3b and 1 – Two mirror image maps - Owl monkey

  17. Touch • Somatosensory Cortex (Cont’d) • Cortical Map Plasticity • Remove digits or overstimulate – examine somatotopy before and after • Maps are dynamic

  18. Touch • Somatosensory Cortex (Cont’d) • The Posterior Parietal Cortex • Involved in somatic sensation, visual stimuli, and movement planning • Agnosia • Astereoagnosia • Neglect syndrome

  19. 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

  20. Pain • Nociception and the Transduction of Painful Stimuli (Cont’d) • Types of Nociceptors • Polymodal • Mechanical • Thermal • Hyperalgeia • Primary and secondary

  21. Pain • Primary Afferents and Spinal mechanisms • First pain and second pain • Referred pain: Angina

  22. Pain • Ascending Pain Pathways

  23. 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

  24. Pain • Ascending Pain Pathways (Cont’d)

  25. Pain • Pain Regulation • Afferent Regulation • Gate theory of pain - Melzack and Wall

  26. Pain • Pain Regulation • Descending Regulation -> • The endogenous opiates • Opioids and endomorphins

  27. Temperature • Thermoreceptors • “Hot” and “cold” receptors • Varying sensitivities

  28. Temperature • Thermoreceptors • Hot and cold receptors

  29. Temperature • The Temperature Pathway • Organization of temperature pathway • Identical to pain pathway • Cold receptors coupled to Ad and C • Hot receptors coupled to C

  30. 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

  31. End of Presentation

  32. Touch • The Spinal cord • Dermatomes- 1-to-1 correspondence with segments • Shingles

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