ch 12 - the somatic sensory system

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• Responds to many kinds of stimuli

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

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

Touch• Mechanoreceptors (Cont’d)

– Small and large receptive fields

– Receptors - receptive field size and adaptation rate

– Two-point discrimination• Receptive field

density• Receptive field size• Computing power• Special neural

mechanisms

Touch• Primary Afferent Axons

– AC– C fibers mediate pain and temperature– Amediates touch sensationsmediates acute, early pain

Touch• The Spinal cord

– Spinal segments (30)- spinal nerves within 4 divisions of spinal cord.

Touch• Spinal cord (Cont’d)

– Divisions of spinal gray matter: Dorsal horn; Intermediate zone; Ventral horn• Myelinated A axons

(touch-sensitive)

Touch• Dorsal Column–Medial Lemniscal Pathway

– Touch and proprioception

Touch• The Trigeminal Touch Pathway

– Somatosensory information from face

Touch• Somatosensory Cortex

– S1 = Area 3b– Adjacent areas:

• Postcentral gyrus: 3a,1,2,• Posterior Parietal

Cortex: 5,7

Touch• Somatosensory Cortex

– Cortical Somatotopy: Homunculus

Touch• Somatosensory Cortex (Cont’d)

– S1: Rat“Barrel cortex” (vibrissae)

– 3b and 1 – Two mirror image maps - Owl monkey

– Cortical Map Plasticity– Remove digits or overstimulate – examine

somatotopy before and after– Maps are dynamic

– The Posterior Parietal Cortex• Involved in somatic sensation, visual stimuli, and

movement planning• Agnosia• Astereoagnosia • Neglect syndrome

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

Pain• Nociception and the

Transduction of Painful Stimuli (Cont’d)

– Types of Nociceptors• Polymodal• Mechanical• Thermal

– Hyperalgeia• Primary and secondary

Pain• Primary Afferents and Spinal mechanisms

– First pain and second pain– Referred pain: Angina

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

Pain• Ascending Pain Pathways (Cont’d)

Pain• Pain Regulation

– Afferent Regulation– Gate theory of pain - Melzack and Wall

Pain• Pain Regulation

– Descending Regulation ->

– The endogenous opiates• Opioids and

endomorphins

Temperature• Thermoreceptors

– “Hot” and “cold” receptors– Varying sensitivities

Temperature• Thermoreceptors

– Hot and cold receptors

Temperature• The Temperature Pathway

– Organization of temperature pathway• Identical to pain pathway

– Cold receptors coupled to A and C– Hot receptors coupled to C

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

End of Presentation

Touch• The Spinal cord

– Dermatomes- 1-to-1 correspondence with segments– Shingles

ch 12 - the somatic sensory system

Documents

senses - somatic senses (touch, pressure, temp, pain) ·...

sensory alterations potter and perry ch. 49

long sensory pathways (somatic sensation)

ch. 46 sensory receptors, neuronal circuits for processing...

trigeminal system. uoanatomy/neuroanat/ somatic sensory:...

the somatic sensory system sensory stimuli that reach the...

14-10 cranial nerves cranial nerves 12 pairs connected to...

somatic sensory receptors. pain. chemoreception (taste ......

sensory systems ch. 39

the somatic sensory system

apr enhanced lecture slides -...

the somatic senses sensory reception of the five senses

somatic senses general sensory system. sensation define...

sensory phys and somatic reflexes

somatic and special senses - fmfranco.com · 1 general...

somatic sensory system aqsa sjuhada department of oral...

nervous system tissue fall 2010 slides system... · 2010....

spinal cord,vertebrae,csf,somatic sensory and motoric...

ch. 8 the somatic sensory system the somatic sensory system...

ch. 7 sensory physiology - francis marion...