Systemic Neuroanatomy: Motor System

Question 1

5 parts of the motor system

Answer 1

pyramidal, extra-pyramidal, corticobulbar, cerebellum, basal ganglia

Question 2

What are the cells of origin for the corticospinal system? Where do they synapse? What kind of motion?

Answer 2

origin: large pyramidal neurons in the primary motor cortex and secondary motor cortex.
mostly synapses on cervical interneurons, with some lumbrosacral LMNs and interneurons.
flexor bias that gives FINE MOTOR CONTROL.

Question 3

What is the course of the corticospinal tract?

Answer 3

In the telencephalon, located in the corona radiata
in the diencephalong, found in the posterior limb of the internal capsule
in the midbrain, found in the cerebral peduncle
in the pons, found in the basis pontis
in the medulla, found in the pyraminds where it decussates
in the spinal cord, found in the lateral funiculus
ONE AXON

(corona radiata –>internal capsule –> cerebral peduncle –> basis pontis –> pyramids (decussation) –> lateral funiculus

Question 4

What four UMN tracts synapse on LMN at all spinal levels?

Answer 4

rubrospinal, lateral vestiubulospinal, pontine reticulospinal, medullary reticulospinal

Question 5

Origin for rubrospinal tract? input from where? course?

Answer 5

red nucleus
gets input from cerebral cortex and cerebellum
fibers exit the red ducleus, decussates, travels through brain stem and lateral funiculus, uses interneurons to synapse on spinal LMN

Question 6

What does the rubrospinal tract do? What other systems are important for its function?

Answer 6

input fro cerebral cortex and cerebellum given to red nucleus
flexor bias; helps with pyramidal fine motor control

Question 7

What happens if you mess with the cortex input to the red nucleus?

Answer 7

rubrospinal tract proble

flexion of upper extremeties and extension of lower extremities, aka decorticate posturing

Question 8

Origin for the lateral vestublospinal tract? input from where? course?

Answer 8

origin: lateral vestibular nucleus
gets input from vestibular apparatus
descends ipsilaterally through brain stem and ventral funiculus and synapses directly on spinal LMNs

Question 9

What does the lateral vestublospinal tract do? What other systems are important for its function?

Answer 9

Extensor bias
helps iwth antigravity tone and upright posture
inhibited by red nucleus

Question 10

What happens if you have a lesion to the red nucleus?

Answer 10

red nucleus can’t inhibit vestibulospinal tract

you see uninhibited extension of all 4 limbs, aka decerebrate posturing

Question 11

Origine for pontine reticulospinal tract? input from where? course?

Answer 11

origine: pontine reticular formation
input: spinoreticular sensory fibers
descends ipsilaterally through the brain stem and ventral funiculus
synapses on spinal LMNs.

Question 12

What does the pontine reticulospinal tract do?

Answer 12

extensor bias

helps maintain extensor tone, esp. in response to noxious stimuli.

Question 13

Origin for the medullary reticulospinal tract? input? course?

Answer 13

origin: medullary reticular formation
input: cortex
descends ipsilaterally through brain stem and ventral funiculus. synapses via interneurons on LMNs

Question 14

What does the medullary reticulospinal tract do?

Answer 14

flexor bias. augments corticospinal and rubrospinal

Question 15

Origin for medial vestibulospinal tract? input? course? function?

Answer 15

origin: medial vestibular nucleus
input from vestibular apparatus
descends ipsilaterally through brainstem and ventral funiculus to synapse on cervical LMNs
function: coordinate head and neck motion with vestibular input to maintain head position

Question 16

What tracts synapse on cervical LMNs exclusively?

Answer 16

medial vestibulospinal tract and tectospinal tract

Question 17

Origin of tectospinal tract? course?

Answer 17

origin: superior colliculus; some in inferiror colliculus
exit the colliculi, decussate immediately, descend in the medial-dorsal brain stem and ventral cervical spinal cord. synapse on LMNs via interneurons.
coordinate head and neck motion w visual (and some auditory) stimuli

Question 18

Function of corticobulbar system

Answer 18

major UMN tract controlling brain stem LMNs

Question 19

How do the corticobulbar and corticospinal tracts differ?

Answer 19

Corticobulbar:

1. innervates brain stem, not spinal LMNs
2. travels in the genu of internal capsule
3. provides both ipsilateral and contralateral innervation to all brain stem LMNs with the exception of the lower half of the face. Lower half of the face receive ONLY contralateral UMN innervation.

Question 20

What does contralateral lower facial weakness indicate?

Answer 20

lesions to corticobulbar system. upper facial strength should be normal becasue of the ipsilateral projection of the corticobulbar tract to the upper half of the face

Question 21

What is pseudobulbar palsy?

Answer 21

bilateral cortical lesions of the corticobulbar tract. generalized facial and bulbar weakness with difficulty speaking and swallowing.