Descending motor pathways

Question 1

Lower motor neuron lesions has what 5 clinical effects?

Answer 1

1) Muscle wasting (Atrophy as not stimulated)
2) Muscle weakness/ reduced power
3) Hypotonia - reduced resting muscle tone
4) Absent tendon reflexes
5) Fasciculation/ fibrillation

Question 2

What are the 3 roles of UMNs?

Answer 2

1) Influence LMN activity
2) Modify local reflex activity
3) Superimpose more complex patterns of movement

Question 3

Other than corticospinal/corticobulbar, what are the 3 other motor pathways?

Answer 3

1) Reticulospinal
2) Vestibulospinal
3) Rebrospinal

Question 4

Corticospinal pathway is mainly involved in what movement?

Answer 4

Voluntary fine precision movements

Question 5

What are the initial effects of selective damage to the corticospinal pathway? 2

Answer 5

1) Flaccid paralysis of contralateral limbs

2) Loss of tendon reflexes

Question 6

After several days following selective damage to the corticospinal tract and initial paralysis what occurs?

Answer 6

Motor function recovers but with hypertonia

Question 7

What are the 3 long terms effects of selective damage to the corticospinal pathway?

Answer 7

1) Spasticity
2) Hypereflexia
3) Permanent inability to carry out fine movements of hands and feet

Question 8

Corticobulbar fibres go from where to where?

Answer 8

Pre central gyrus to cranial nerve nuclei

Question 9

Cranial nerve motor nuclei are located where within the brainstem?

Answer 9

The floor of the 4th ventricle (pons)

Question 10

Corticobulbar fibres travel from the pre central gyrus to the cranial nerve nuclei via what?

Answer 10

Genu of the internal capsule

Question 11

Corticospinal fibres travel from where to where?

Answer 11

Pre central gyrus to the ventral grey horn of the spinal cord

Question 12

Are corticospinal and corticobulbar fibres UMNs or LMNs?

Answer 12

UMNs

Question 13

Are cranial nerves UMNs or LMNs?

Answer 13

LMNs

Question 14

Corticospinal fibres pass from pre central gyrus to brain stem via what?

Answer 14

Posterior limb of internal capsule

Question 15

What is the root of corticospinal fibres to the ventral grey horn?

Answer 15

From pre central gyrus via posterior limb of internal capsule
Descend through cerebral peduncles and ventral pons to pyramids
85% of fibres decussate at pyramids and descend through spinal cord in contralateral lateral corticospinal tract
15% of fibres descend in ipsilateral pyramids and ipsilateral anterior corticospinal tract through spinal cord

Question 16

The right pre central gyrus controls which side of the body?

Answer 16

The left

Question 17

Where do corticospinal neurones decussate?

Answer 17

85% within the medulla at decussation of pyramids

15% at level of exit through the spinal cord via the anterior white commissure

Question 18

Where do corticospinal neurones and LMNs synapse?

Answer 18

Contralateral ventral grey horn

Question 19

Where do corticospinal fibres descend within the spinal cord?

Answer 19

85% in contralateral lateral corticospinal tract

15% in ipsilateral anterior corticospinal tract

Question 20

The posterior limb of the internal capsule is somatotypically mapped, which lies most posterior, the arm of leg?

Answer 20

leg most posteriorly

Arm most anteriorly and trunk in the middle

Question 21

The cerebral peduncles are somatotypically mapped, which part of the body lies closest to the interpeduncular fossa and which furthest away?

Answer 21

Leg furthest away
Then trunk then arm
Then face closest to interpeduncular fossa

Question 22

The lateral corticospinal tract is somatotypically mapped, does the arm or leg lie most anterior?

Answer 22

arm lies most anterior

Leg lies most posterior

Question 23

How do LMNs leave the spinal cord?

Answer 23

Via the ventral grey horn as ventral rootlets to form spinal nerve

Question 24

Name the 8 cranial nerve motor nuclei?

Answer 24

1) CN3 - occulomotor
2) CN4 - trochlear
3) CN5 - trigeminal
4) CN6 - abducens
5) CN7 - facial
6) CN9 and 10 - glossopharyngeal and vagus
7) CN11 - accessory
8) CN12 - hypoglossal

Question 25

Corticobulbar fibres to all motor cranial nerve nuclei except hypoglossal and facial take what path?

Answer 25

From pre central gyrus via genu of internal capsule
Give some fibres to contralateral and some to ipsilateral nucleus
(MOST) CN NUCLEI ARE SERVED BILATERALLY

Question 26

Corticobulbar fibres synapse with LMNs where?

Answer 26

Motor cranial nerve nuclei

Question 27

How are hypoglossal motor nuclei served?

Answer 27

By contralateral corticobulbar fibres

Question 28

How does the facial motor nuclei differ to other cranial nerve nuclei?

Answer 28

Split into upper and lower part
Upper part sends fibres to muscles of upper face
Lower part sends fibres to muscles of lower face

Question 29

How is the upper part of facial motor nucleus served?

Answer 29

Served by bilateral corticobulbar fibres

So upper face is served bilaterally

Question 30

How is the lower part of facial motor nucleus served?

Answer 30

Served only by contralateral corticobulbar fibres

Lower face is served contralaterally

Question 31

How do LMN from the facial motor nucleus pass to the facial muscles?

Answer 31

Via the facial nerve
Passes out of skull via internal acoustic meatus
Passes through facial canal
Out of stylomastoid foramen
Branches into 5 branches within the substance of the parotid gland