Corticospinal tract Flashcards
what is the pathway of the descending pathway from M1
- output neurons leave M1
- travel via the internal capsule (posterior limb) to the midbrain, pons, and medulla
- neurons enter the pyramids (in medulla)
- most neurons decussate at the pyramids to the lateral CST on the contralateral side
- neurons travel down lateral CST or ventral/anterior CST until they synapse onto interneurons / MNs in the ventral horn of the spinal cord
what % of neurons are in the lateral CST
80-90%
what % of neurons are in the ventral/anterior CST
10-20%
what area in the brain is the largest contributor to the CSTs
M1 - around 36% of CST neurons
what occurs with damage to the lateral CST below the pyramidal decussation cause
ipsilateral side of the body
what occurs with damage to the lateral CST above the pyramidal decussation cause
contralateral side of the body
what is the innervation pattern of the anterior/ventral CST neurons
bilateral innervation
- damage causes weakness but not complete paralysis
what are the two types of CST neurons
CST neurons = synapse with interneuron in SC before synapsing with spinal MNs
corticomotoneuronal cells (CM cells) = synapse directly onto spinal neurons
what is a pyramidotomy
surgical procedure where all descending fibres of the pyramidal tract are severed preventing motor commands from travelling from the brain to the SC or muscles
- prevents info from being transmitted to the SC via the CSTs
what is the source of CM cells
M1
- originate on the anterior bank of the central sulcus and synapse directly on spinal MNs
what do the axonal branches of CM cells synapse onto
- networks of surrounding neurons
what do the axon of single CM cells synapse onto
spinal neuron of many different muscles
what is the proportion of CST neurons from different parts of the brain (from highest to lowest)
M1 - 36%
S1 - 30%
SMA - 25%
PMd - 7%
PMv - 2%
