Motor System

Question 1

Where are the corticospinal and corticobulbar fibres loacted?

Answer 1

Corticospinal and corticobulbar fibres are both located in the posterior limb of the internal capsule. The corticospinal fibres are nearer the retrolenticular region, corticobulbar fibres are nearer the genu.
 

Question 2

Where are the cell bodies of upper motor neurons in the corticospinal tract primarily located?

Answer 2

Principally in the primary motor cortex

Question 3

put the structures of the corticospinal into the correct order, starting at the level of the cerebral hemispheres.

Answer 3

Correct order: Primary motor cortex -> Corona radiata -> Internal capsule -> Crus cerebri -> Pyramid -> Decussation of the pyramid -> Lateral corticospinal tract -> Ventral horn

Question 4

Where are the cell bodies of lower motor neurons located?

Answer 4

? In the ventral grey horn of the spinal cord. Their axons exit the spinal cord in the ventral root, and merge with the dorsal root to form a mixed spinal nerve.

Question 5

What happens to the majority of descending cortico-spinal motor axons at the decussation of the pyramids?

Answer 5

They cross (decussate) to the contralateral side

Question 6

Apart from their location, what is the main difference between the fibres of the lateral and ventral corticospinal tract?

Answer 6

Fibres in the lateral tract decussated in the medulla; fibres in the ventral tract are ipsilateral and will decussate in the spinal cord close to the vertebral level where their target lower motor neurons are located

Question 7

Do upper motor neurons in the lateral and ventral corticospinal tracts synapse on lower motor neurons in the ipsilateral or contralateral ventral grey horn of the spinal cord?

Answer 7

Nearly all synapse on to lower motor neurons on the contralateral side