Touch and Proprioception

Question 1

Posterior Column/ Medial Lemniscus System function?

Answer 1

Light touch and pressure (2 point discrimination, vibration) proprioception/position sense

Question 2

Touch and Pressure receptors

Answer 2

Meissners Corpuscle and Pacinian corpuscle

Question 3

Proprioception receptors

Answer 3

GTO’s and Muscle spindles

Question 4

Where do lateral enter the spinal cord

Answer 4

C1-T6

Question 5

Where do medial afferents enter the spinal cord

Answer 5

T7 and below

Question 6

describe how A- beta fibers inhibit pain

Answer 6

A-beta fibers excite inhibitory interneurons in substantia gelatinosa which, inhibit nociceptive afferents. Prevents C and A delta fibers from exciting spinothalamic tract fibers.

Question 7

Were do third order neurons from VPL go to get to the S-1

Answer 7

they must go through posterior limb of internal capsule to reach primary somatosensory cortex

Question 8

LE and UE fibers

Answer 8

LE course medially while UEs course laterally

Question 9

Maps on Brodmann areas

Answer 9

Proprioception, light touch, light touch, deep pressure

Question 10

Describe connections between S-1 and other cortical areas

Answer 10

S-1 sends projections to M-1 (area 6) and to S-2 which deals with more abstract aspects of touch (texture shape)

Question 11

Flow of info starting at primary afferents and ending at S-1 and postcentral gyrus

Answer 11

First order afferents (soma in DRG) enter dorsal horn (if they are going directly to cortex there is no synapse here) and ascend to fasiculus gracilis/cuneatus of the caudal medulla. Second order neurons course from dorsal to ventral at internal arcuate fibes and cross midline to form contralateral medial lemniscus then ascend to VPL nucleus of thalamus. Third order neurons go from thalamus to S-1 or postcentral gyrus