Descending Tracts

Question 1

What are the pyramidal tracts?

Answer 1

Latera corticospinal tract
Anterior corticospinal tract
Corticobulbar tract

Question 2

What do the pyramidal tracts control?

Answer 2

Voluntary movement
Corticospinal supplies the musculature of the body
Corticobulbar supplies the musculature of the head and neck

Question 3

Where do the pyramidal tracts originate?

Answer 3

Cerebral cortex (Motor cortex/Pre-motor area/Supplementary motor area/somatosensory cortex)

Question 4

Describe the path of the lateral corticospinal tract.

Answer 4

Inputs from Cerebral cortex
Descend through internal capsule (white matter pathway between thalamus and basal ganglia)
midbrain (crus cerebra),
pons,
medullary pyramids, - divides into anterior and lateral tracts
Lateral corticospinal tract decussates and descends contralaterally in spinal cord
Terminate in ventral horn at spinal level supplied.
(Synapse with alpha-motorneurone or interneurone)

Question 5

Describe the path of the anterior corticospinal tracts.

Answer 5

Cerebral cortex 
Descend through internal capsule
the midbrain (crus cerebri)
Pons
Medullary pyramids
Descend to cervical and thoracic levels
Decussate at a certain vertebral level and synapse with lower motor neurones in ventral horn

Question 6

Where do the corticospinal tracts decussate?

Answer 6

Lateral - in the medulla

Anterior - spinal cord

Question 7

Why is the corticospinal tract vulnerable to damage from haemorrhage?

Answer 7

Passes through the internal capsule which is innervated by the medial meningeal artery.
The internal capsule is susceptible to compression from haemorrhagic bleeds, known as a ‘capsular stroke‘

Question 8

What does the corticobulbar track supply?

Answer 8

Cranial nerves.

Muscles of head and neck

Question 9

Where does the corticobulbar tract originate?

Answer 9

Cortex:
30% motor cortex
30% premotor area and supplementary motor area
40% somatosensory cortex

Question 10

Describe the path of the corticobulbar tract.

Answer 10

Cerebral cortex
Internal capsule
Brainstem - decussates
Terminate on cranial nerve motor nuclei in brainstem, midbrain, pons, medulla.
Synapse with lower motor neurones.

Question 11

Where does the corticobulbar tract decussate?

Answer 11

May fibres from corticobulbar tract innervate lower motor neurones bilaterally

except:

Upper motor neurones for facial nerve have contralateral innervation

Upper motor neurones for hypoglossal nerve (12) only provide contralateral innervation

Question 12

Where do the pyramidal pathways terminate?

Answer 12

Lateral corticospinal - contralateral spinal cord ventral horn
Anterior corticospinal - contralateral spinal cord ventral horn
Corticobulbar - Contralateral (and some ipsilateral) motor cranial nerve nuclei.

Question 13

What are the extrapyramidal tracts

Answer 13

Brainstem pathways:
vestibulospinal
tectospinal
Reticulospinal
Rubrospinal/rubrobulbar
Olivospinal

Question 14

What do the extrapyramidal tracts control?

Answer 14

Automatic, involuntary movements and tone, balance, posture

Question 15

Origin of vestibulospinal tract?

Answer 15

Vestibular nuclei in pons

Question 16

Path of vestibulospinal tract

Answer 16

Vestibular nuclei pons
Ipsilateral spinal cord
Terminates on alpha motor neurones and interneurones

Question 17

Function of vestibulospinal tract

Answer 17

Balance and posture by innervating anti-gravity muscles (flexors of arm and extensors of leg)

Question 18

Origin of tectospinal tract

Answer 18

Tectum (colliculi) of midbrain (Superior colliculi (visual input) inferior colliculi (auditory input).

Question 19

Path of tectospinal tract?

Answer 19

(receives input from optic nerves)
Tectum of midbrain
Decussates immediately in midbrain
Spinal cord
Terminates in cervical cord and brainstem nuclei

Question 20

Function of tectospinal tract

Answer 20

Directing head movement in response to visual and auditory stimuli

Question 21

Origin of reticulospinal tract

Answer 21

Reticular formation in pons (medial reticulospinal tract) and medulla (lateral reticulospinal tract)

Question 22

Path of reticulospinal tract

Answer 22

Remains ipsilateral (partially decussates in brainstem)
Innervates motor neurone, regulating posture and rhythmic movement.

Question 23

Function of reticulospinal tract

Answer 23

Automatic movement
Medullary tract (lateral) innervates flexor reflexes, inhibits extensor - inhibits voluntary movement and reduces tone

Pontine (medial) facilitates extensor reflexes - facilitates voluntary movement and increases tone

Question 24

Origin of rubrospinal/rubrobulbar tract

Answer 24

Red nucleus of midbrain

Question 25

Path of rubrospinal/rubrobulbar tract

Answer 25

Red nucleus, midbrain
Decussates immediately in midbrain
Terminates on alpha motorneurones/interneurones

Question 26

Function of rubrospinal/rebrobulbar tracts

Answer 26

Facilitate flexion - controls flexor tone, fine control of hand movements.
Rubrobulbar - controls tone of facial muscles

Question 27

Where do the extrapyramidal tracts decussate?

Answer 27

Vestibulospinal - ipsilateral
Tectospianl - immediately in midbrain
Reticulospinal - ipsilateral (partially in brainstem)
Rubrospinal/rubrobulbar - immediately in midbrain

Question 28

Why does damage to the corticobulbar tracts only result in mild muscle weakness? What is the exception to this?

Answer 28

Mostly bilateral innervation of LMN

Except CNXII - lesion of UMN will result in spastic paralysis of contralateral genioglossus - deviation to contralateral side to lesion

CNVII - UMN lesion will result in spastic paralysis of muscles in contralateral lower quadrant of face

Question 29

How does UMN and LMN lesion of CNXII differ?

Answer 29

In UMN tongue away from lesion as contralateral innervation

In LMN lesion, tongue toward lesion.