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Physiology 3120 Lecture Notes - Postcentral Gyrus, Central Sulcus, Evoked Potential

Course Code
Tom Stavraky

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Human Physiology
Friday, October 23, 2009
Somatosensory System II
Somatosensory cortex located in the post-central gyrus (posterior/caudal to the central sulcus)
Properties (each hemisphere is organized this way)
(1) Somatotopic organization
Leg (medial) trunk arm face (lateral)
This organizational structure is called a homunculus (“little man”)
Distorted because of differences in density of receptors in a certain body part
(highest in fingers & lips); more sensitive areas take up more cerebral surface area
Understanding of this organization based on. . .
Recording from population of neurons/single neuron
oStimulation of a nerve produces an evoked potential in the brain
(measured with an electrode in the brain)
Lesions (several different methods; strokes in vivo)
oLesions of certain brain areas produce certain deficits, allowing us to
understand the function of that brain area
oBecause it is SS cortex, patient will feel a “tingling” sensation
oAllows us to know the areas of the body that innervate that particular
region of cortex
oEpilepsy in the post-central gyrus can start medially & move laterally
Present at birth, but also shows cortical plasticity
Example: someone who is born sighted, but later become blind & use to learn
Braille, the hand area of the cortex will expand
(2) Columnar organization
All neurons in a column of cortex have very similar properties
Modality-pure (particular type of receptor) on the same part of the body
Faithful transmission
SS system dominated by dorsal-column medial lemniscal system (90%)
No convergence in DCML system; convergence only occurs in the
spinothalamic system
Reconstruction starts to occur at the level of cortex; involves processing rather than just gathering of
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