Download PCL - mmc7

PCL:
Cerebral Cortex
Circle of willis
Sensory Pathways
Dorsal
The dorsal column conducts proprioception, vibration, some light touch and twopoint discrimination. Below the level of a lesion, these are diminished. Tingling,
electric-shock-like sensations, clumbsiness, numbness and band-like sensations can
be felt. In a cervical cord lesion, Lhermitte’s phenomenon can occur. In Lhermitte’s
phenomenon, electric-shock sensations radiate down the trunk and limbs on neckflexion.
Spinothalamic (anterolateral)
A lesion within the spinothalamic tracts of the cord that causes conduction to fail
produces changes in pain and temperature sensation below its level. External lesions
produce changes to pain and temperature sensation beginning in the lower limbs
and ascending to the level of the lesion. In a syrinx, a cavity in the centre of the
spine, the lower limbs and sacral areas can be spared. (Kumar)
UMN vs LMN
Upper motor neurons: an upper motor neuron originates in the cerebral cortex or
brainstem and conducts nerve impulses down to the appropriate spinal level. An
upper motor neuron lesion is also known as a pyramidal lesion.
Lower motor neurons: these carry nerve impulses from the spinal cord (or brainstem
for cranial nerves) to the muscle
Decussation: the crossing over of upper motor neurons
Suppose that left-sided facial weakness arises. Where could this pathology be?
1. Left side lower-motor neuron
2. Right side upper motor neuron
How could these causes be differentiated from each other? A left-side lower motor
neuron lesion will paralyse the entire face. However, at least theoretically, an upper
motor neuron lesion will spare the upper part of the contralateral side. This is
because the upper facial muscles are supplied by both the left and right cortex.
(You can see that although most neurons cross over, some instead supply the
ipsilateral forehead)
Refs:
Kumar & Clark
Clarke, queen square textbook