25. DPT 746: Lec 11 Corticospinal + corticobulbar tracts

Main function of corticospinal tract

Control of voluntary, skilled movements

Why is it called the corticospinal tract? (break down the name)

Because it has descending fibers that run from the cortex to the spinal cord

Does corticospinal tract deal with upper or lower motor neurons?

Upper

Where does the corticospinal tract originate in the brain? (6 areas)

Primary motor cortex (40%)

Supplementary motor cortex

Premotor cortex

Primary sensory cortex

Parietal lobe

Cingulate gyrus

First area of the corticospinal tract, broad and fan-shaped

Corona radiata

From corona radiata, fibers come together from the fan and become the...

Posterior limb of the internal capsule

What structure do corticospinal tracts enter after becoming part of the internal capsule?

Brainstem

Where do corticospinal tract fibers go after passing through the brainstem?

Through the crus cerebri (cerebral peduncle) of the midbrain

Where do corticospinal tracts go after passing through crus cerebri?

Basilar area of the pons (ventral side of pons)

Where do corticospinal tracts go after passing through the basilar side of the pons? Ipsi or contralateral side?

Pyramid area of medulla, ipsilateral side

List out the entire path of the CST fibers, beginning with corona radiata (5)

Corona radiata ->

Posterior limb of internal capsule ->

Crus cerebri of midbrain ->

Basilar pons ->

Pyramid of medulla (ipsilateral side)

Define corticobulbar tracts

Tracts that come off the CST during it's descent in the brainstem to activate motor cranial nerve nuclei

What part of the cortex gives rise to corticobulbar tracts?

Lateral portion of primary motor cortex, which makes sense because this is the face region of the motor homonculus

What muscles are controlled by corticobulbar tracts?

Muscles of the face, jaw and tongue. Innervated by cranial nerve nuclei

Another name for corticobulbar tracts?

Corticonuclear tracts

Describe the ipsi vs. contralateral distribution of corticobulbar fibers:

All corticobulbar fibers distribute to CN motor nuclei on ipsilateral side, EXCEPT facial nerve (CN VII) which distributes contralaterally.

What part of the brainstem has the synapse areas for corticobulbar tracts? (i.e. where do they meet cranial nerve nuclei?) (3 areas)

AFTER corona radiata and internal capsule:

Midbrain

Pons

Medulla

All have their own synapse areas

Do CST tracts descend ipsi or contralaterally through the brainstem?

Ipsilaterally until they reach the pyramids of medulla

Describe the pyramidal decussation of CST. Percentage of total fibers? Area?

80% of CST axons cross midline in decussation of pyramids at medullary-spinal cord junction.

CST fibers that decussate in the medulla descend via what area of the spinal cord? Which funiculus?

Descend via the lateral CST (area) in

lateral funiculus of spinal cord.

What type of neurons do lateral CST fibers synapse on? Is this a direct or indirect synapse?

Synapse on alpha and gamma motor neuron fibers.

Act directly (activate alpha and gammas) and indirectly (inhibit alpha and gamma via interneurons).

What percentage of total CST fibers do NOT decussate at the pyramid of medulla?

20% of total available CST fibers

Describe the two pathways of the 20% CST fibers that don't decussate at pyramids of medulla. Where do they go? Do they decussate?

Half of these axons (so 10% of total CST axons) continue as ventral CST in anterior funiculus, later decussate in white commissure

Half (so 10% total CST axons) enter the lateral CST on the same side

What percentage of TOTAL CST fibers descend in the lateral CST area? Are these ipsi or contralateral?

90% of TOTAL CST fibers in lateral CST area. 80% are contralateral fibers that have decussated in pyramids of medulla. 10% are ipsilateral fibers that did not decussate

What percentage of TOTAL CST fibers go to the ventral CST area in the anterior funiculus?

10% of TOTAL CST fibers travel in the ventral CST area in the anterior funiculus

How is the internal capsule organized? Where are corticospinal and corticobulbar tracts in internal capsule?

Internal capsule organized somatotopically, has distinct regions for each descending tract. Corticospinal and corticobulbar tracts are adjacent

Path of travel for CST axons that regulate processing of incoming lemniscal sensory information:

Arise from primary sensory cortex->

Terminate in secondary sensory nuclei in brainstem and spinal cord

Which function of the descending tracts do the CST primary sensory cortex neurons perform?

Neurons from primary sensory cortex modulate incoming sensory activity to the brain and spinal cord

The 80% decussated lateral CST fibers travel in the ______ funiculus and terminate on ______. What musculature do these neurons control?

Travel in the lateral funiculus.

Terminate directly and indirectly on LMNs associated with distal musculature (skilled hand and finger movements).

The 20% uncrossed CST fibers travel in the _____ and _____ (2 regions)

10% in the lateral CST area (in conjunction with the 80% decussated fibers)

10% in anterior CST area

The (10%) anterior CST fibers descend in the ______ funiculus and terminate on ______. What muscles are supplied by these fibers?

Descend in the anterior funiculus, terminate on LMNs that supply medial musculature

Where do the (10%) anterior CST fibers decussate?

After pyramidal decussation, lower in the spinal cord, through the ventral white commissure

A small number of anterior CST axons terminate ______ to cortical cells of origin.

Ipsilateral

An isolated lesion to CST in pyramids of medulla would cause ______ (ipsi or contra?) weakness of hand movements.

Contralateral

Lesions involving CST and other descending fibers (pre-medulla) will present with what "classic" upper motor neuron symptoms? (4)

Contralateral spastic hemiplegia

Hypertonus

Hyperreflexia

Plantar extensor responses

Lesions in lateral CST produce hand weakness on the ______ (ipsi or contra?) side if the lesion is below medulla?

Ipsilateral side