Somatosensory Physiology

Question 1

ascending somatosensory pathway

Answer 1

dorsal column-medial lemnisucs system

Question 2

relays

Answer 2

touch, vibration sense, and limb proprioception

Question 3

spinal tract consists of

Answer 3

large diameter primary afferents

neurons of lamina III and IV of the dorsal horn

Question 4

pathway of the dorsal column-medial lemnisucs system

Answer 4

1st neuron - dorsal root ganglion cells
1st wire bundle - dorsal columns are made of the central branches of DRT axons run ipsilaterally
2nd neuron - ipsilateral dorsal column nuclei 1. nucleus gracilis 2. nucleus cuneatus in the medulla
2nd wire bundle - medial lemnisucs crosses over (prior to crossing over the fiber bundles called the internal arcuate fibers
3rd neuron - contralateral ventralposterial lateral nucleus of the thalamus
3rd wire bundle - contralateral internal capsule
4th neuron - in the contralateral primary somatosensory cortex in the parietal lobe

Question 5

somatotopy

Answer 5

as you go up the spinal tract, white matter tracts get bigger and bigger because more axons are coming in
this is how location is encoded - it’s encoded every step up the way up the spinal tract