Ascending and Descending tracts, Lesions

Question 1

Name the 2 pyramidal descending tracts.

Answer 1

Corticospinal

Corticobulbar

Question 2

Name the 4 main extra-pyramidal descending tracts.

Answer 2

Rubrospinal
Reticulospinal
Vestibulospinal
Tectospinal

Question 3

Describe the route of the corticospinal tract.

Answer 3

Originates- Primary motor cortex, then descends in upper motor neurons through the corona radiate, through the internal capsule (between the thalamus and lentiform nucleus (globus pallidus & putamen), then through the crus cerebri of the midbrain, through the pons, and to the medulla. At the base of the medulla (medullary pyramids) between 75-90% of the corticospinal fibres DECUSSATE and descend contralaterally as the lateral corticospinal tract. The remaining few fibres ascend ipsilaterally as the anterior corticospinal tract. The lateral corticospinal tract neurons ascend in the lateral/dorsal part of the spinal column; the anterior neurons ascend more ventromedially.
UMN synapse with LMN in the ventral horn.

FUNCTION: control of voluntary, skilled, discrete movements.
LESIONS above the medullary level: contralateral side affected.

Question 4

Describe the function of the corticobulbar tract.

Answer 4

Motor innervation of several cranial nerves,
This tract runs parallel to the corticospinal tract, and has the same input, passing through the internal capsule, the brainstem, and then synapsing with the cranial nerves.
Many corticobulbar fibres innervate cranial nerves bilaterally.

Question 5

How do the extra-pyramidal tracts differ from the pyramidal tracts?

Answer 5

PYRAMIDAL:

• corticospinal and corticobulbar.
• voluntary control of movement of head body muscles
• originate in the cerebral cortex (mainly the primary motor cortex)

EXTRA-PYRAMIDAL:

• rubrospinal, reticulospinal, tectospinal and vestibulospinal
• do not reach the level of the cerebrum; orginate in the brainstem
• involuntary and automatic control of movement

Question 6

Describe the rubrospinal tract.

Answer 6

Rubrospinal tract originates in the “red nucleus” of the midbrain. Fibres ascend close to the corticospinal tract.
Function is not known. Fibres emerge from the red nucleus and decussate in the pons.

Question 7

Describe the tectospinal tract.

Answer 7

Tectospinal tract originates in the superior colliculus of the midbrain. It recieves visual input via the optic nerve, as well as some auditory and somatosensory inputs, helping to create a picture of the world around you. Enables reorientation of the head and eyes towards a new stimulus.
After leaving the superior colliculus, the tectospinal fibres quickly decussate, and project in the vetromedial aspect of the spinal cord.
This tract terminates in the cervical levels of the spinal cord.

Question 8

Describe the vestibulospinal tract.

Answer 8

Vestibulospinal tract originates in the vestibular nuceli (pons and medulla), which receives input from the organs of balance, eg. the vestibular labyrinth of the inner ear. The motion of fluid in the cavities of the temporal bone, which are closely linked to the cochlea, results in movements of hairs and nerve transmission via the vestibulocochlear nerve (CNVIII).
This tract remains IPSILATERAL, and fibres control balance and posture, by innervating anti-gravity muscles eg extensors of the legs.

Question 9

Describe the course of the reticulospinal tract.

Answer 9

Reticulospinal tract originates in the pontine and medullary reticular formations.
Axons from the pontine formation ascend in the pontine (medial) reticulospinal tract; BALANCE AND ANTIGRAVITY, maintaining posture. IPSILATERAL

Axons from the medullary reticular formation ascend in the medullary (lateral) reticulospinal tract- OPPOSITE, reduces muscle tone. BILATERAL

Question 10

Which brain area would a stroke involving the anterior cerebral artery affect? What would be the consequences?

Answer 10

Frontal lobe.

Contralateral face, leg, arm weakness, ataxia, abulia (absence of willpower)

Question 11

Which brain area would a stroke involving the middle cerebral artery affect? What would be the consequences?

Answer 11

Temporal lobe, parietal lobe, posterior frontal.
Contralateral face, leg, arm weakness, sensory loss to all modalities.
Visuo-spatial neglect.
If dominant side affected- alexia, agraphia, acalculia, aphasia.

Question 12

Which brain area would a stroke involving the posterior cerebral artery affect? What would be the consequences?

Answer 12

Occipital lobe.
Visual and sensory deficits
Thalamus affected- numbness, tingling, chronic pain.

Question 13

Which brain area would a stroke involving the anterior inferior cerebellar artery affect? What would be the consequences?

Answer 13

Lateral pontine syndrome.
Ipsilateral- limb ataxia
Ipsilateral- Horner’s syndrome
Contralateral sensory loss- pain/ temp

Question 14

Which brain area would a stroke involving the posterior inferior cerebellar artery affect? What would be the consequences?

Answer 14

Lateral Medulla (wallenberg syndrome)
Vertigo, nausea/ vomitting, hiccups.
Contralateral sensory loss (pain/ temp)
Ipsilateral sensory loss, Horner’s syndrome, pharyngeal and laryngeal paralysis.

Question 15

Which brain area would a stroke involving the basilar artery affect? What would be the consequences?

Answer 15

Pons- Locked in syndrome
complete paralysis of nearly all muscles (voluntary) except vertical eye movements and blinking,
PAtient is aware.
Gaze palsies.