COGS 17 Lecture Notes - Lecture 11: Ventral Posterior Nucleus, Posterior Grey Column, Parietal Lobe
Somatosensory pathways
● 2 major pathways for somatosensory information
○ SPINOthalamic pathway: Free nerve ending → enter through dorsal
horn of spinal cord → contralateral side into the brain → left VPN
(ventral posterior nucleus) of thalamus → projects to the left cortex of
S1 (primary sensory projection area)
■ Cross over in spinal cord
○ Medial lemniscal pathway: Encapsulated nerve ending through right
side of the spinal cord → enter through dorsal horn but doesn’t
synapse where it enters. Continues on the same axon to the medulla
(medial lemniscal) → goes to contralateral s1 in left cortex
■ Cross over in medulla
■ If encapsulated nerve ending entering spinal cord through the
left side → goes to medulla and then VPN on the right →
projects onto s1 cortex on the right side
○ Brown-sequard syndrome: damage to only one side of spinal cord →
lose touch on ipsi-lateral side of the injury, loss of temp/pain on
contralateral side
● 2 major pathways through the brain
○ Input from left go to the right, and input from the right go to the left
○ Encapsulated nerve ending goes through medulla
○ Going from s1 to s2 → crossover such that any info from medial
lemniscal pathway goes to both areas of s2 through crossing of
corpus callosum
● Somatosensory cortex, penfield map
○ S1 → posterior to central sulcus
■ Parietal lobe
■ Postcentral gyrus
○ Topological maps - preserve spatial relationships of sensory surface
○ Magnification - hands and mouth, high acuity=detail discrimination
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