Posted by Demi from IP 18.104.22.168 on June 08, 2012 at 14:34:15:
In Reply to: Why? posted by Valery on June 05, 2012 at 09:46:46:
The posterior columns mediate tactile discrimination, vibratory sensation and recognition of joint and muscle sensation. The first order neurons are located in the dorsal root ganglia and form fasciculus gracilis (lower ext.) and fesciculus cuneatus (upper ext.).
These neurons finish in n.gracilis and n. cuneatus(sec.order neuron). Then give off axons and internal arcuate fibers that decussate and form the m.lemniscus.
M.lemniscus through contralateral brain steam terminates in VPL n. of the thalamus, which projects through the posterior limb of internal capsula to the postcentral gyrus, primary somatosensory cortex (Br.3,1,2).
So if lesion happens ABOVE DECUSSATION, result will be contralateral loss of dorsal column modalities. If the lesion happens on the level of spinal cord before decussation, that would result in ipsilateral vibratory and sensory loss. All the best.
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