Somatosensory System

Question 1

Three seperate systems :

Answer 1

Exteroceptive: external stimuli

Proprioceptive: body position

Interoceptive: body conditions (temp blood pressure)

Question 2

Pacinian corpuscle

Answer 2

Sensitive to sudden or vibrating stimulus

1 type of touch receptor

Question 3

Free nerve endings

Answer 3

Temperature and pain

Question 4

Pacinian corpuscles

Answer 4

Adapt rapidly. Large and deep. Onion like.

Respond to sudden displacements of skin

Question 5

Merkels disks

Answer 5

Gradual skin indentation

Question 6

Ruffini endings

Answer 6

Gradual skin stretch

Question 7

Dermatome

Answer 7

Area of body innervated by the left and right dorsal roots of a given segment of spinal cord

Skin area connected to a single sensory spinal nerve

Question 8

Info from touch receptors in head

Answer 8

Enters CNS through cranial nerves

Question 9

Info from receptors below head

Answer 9

Enters spinal cord and passes toward the brain (31 segments)

Question 10

Dorsal column medial-lemnisucs system

Answer 10

1 pathway do somatosensation

Mainly touch a proprioception

First synapse in dorsal column nuclei of medulla

Question 11

Anterolateral system

Answer 11

2 somatosensory pathway

Mainly pain and temperature

Synapse upon entering spinal cord

Three tracts: spinothalamic, spinoreticular, spinotectal

Question 12

Primary somatosensory cortex (S1)

Answer 12

Postcentral gyrus

Somatotopic organization (somatosensory homonculus) 
^More sensitive more cortex 

Input Largely from contralateral

Question 13

S||

Answer 13

Mainly input from S1

Somatotopic

Input from both sides of body

Much output from both S1 and S2 goes to association cortex in posterior parietal lobe

Question 14

Somatotopy of 1

Answer 14

Map of body surface sensation onto specific areas of brain

Evidence:

Electrical stimulation of S1

Record activity of a single neuron and determine site of receptive field on body

Not scaled like human body

Question 15

Astereognosia

Answer 15

Inability to recognize objects by touch

Pure cases rare

Question 16

Asomatognosia

Answer 16

Failure to recognize parts of ones own body

Question 17

Phantom limb

Answer 17

Intact cortex but damage in periphery experience a continuing sensation of an amputated body part.

Question 18

2 possible explanations of phantom limb

Answer 18

1. area of somatosensory cortex reorganizes it’s connections and becomes responsive to other parts
2. Irritation of nerves in the stump which sends signals to S1 areas that represent amputated part

Question 19

Relieve phantom pain

Answer 19

Mirror study:

Combo of visual and tactile experience of the “good” hand had altered the activity in opposite S1 area

Question 20

Circuitry identified by these studies:

Answer 20

1. Electircal stimulation of periaqueductal gray had analgesic effects
2. PAG and other brain areas have opiate receptors
3. Excistence of endogenous opiates (natural analgesics) -endorphins

Question 21

Events that limit pain ( Melzack and Wall) Gate theory

Answer 21

Certain areas of spinal cord receive messages from other receptors in the skin and from brain - if active they close the “gates” fro the lib messages

Through opiod mechanisms

PAG activated by painful stimuli

Question 22

Stimuli that induce analgesia

Answer 22

Long distance running

Sexual activity

Certain kinds of music

Certain kinds of lingual stimuli = release endorphins and enkephalins. Brakes on further pain

Intermittent or low intensity continuous shock = releases endorphins and enkephalins

High intensity shock decrease pain sensitivity without inducing endorphins and enkephalins release

Question 23

2 non pharmaceutical treatments for controlling pain

Answer 23

1. Acupuncture

2. Transcutaneous electrical nerve stimulation