L38 Organization of the Motor System

Question 1

What sends very coarse signals that need to be modulated by the Basal ganglia, cerebellum and sensory systems?

Answer 1

the cortex

Question 2

what are the voluntary motor systems?

Answer 2

• corticospinal
• corticobulbar
• rubrospinal
• pontine/medial reticulospinal
• medullary/lateral reticulospinal

Question 3

what are the involuntary motor systems?

Answer 3

• lateral vestibulospinal
• medial vestibulospinal

*No cortical control of these!

Question 4

what are the motor sensory input systems?

Answer 4

• muscle spindles
• DCML
• ALS

Question 5

what descending motor tracts make up the ventromedial pathways?

Answer 5

• pontine reticulospinal
• lateral reticulospinal
• medial vestibulospinal

Question 6

what descending motor tracts make up the lateral pathways?

Answer 6

• medullary reticulospinal
• corticospinal
• rebrospinal

Question 7

medial pathways are biased for?

Answer 7

extension/abductor

Question 8

lateral pathways are biased for?

Answer 8

flexion/adduction

Question 9

describe Amyotrophic Lateral Sclerosis (Lou Gehrig’s Disease)

Answer 9

• progressively weakens and wrecks LMN
• eventually wreck pyramidal tracts and precentral gyrus (primary motor area)
• death by respiratory arrest
• die within 3-5 years of dx

Question 10

what do spinal cord diseases usually affect?

Answer 10

motor and somatosensory tracts in the white matter

but may also affect motor neurons of anterior horn and sensory neurons of the dorsal horn

Question 11

what will an anterior spinal artery occulusion (infarction) compromise?

Answer 11

compromise =

• 2nd order motor neurons in ant. horn
• lateral corticospinal tract
• anterior corticospinal tract
• ALS - pain/temp

Question 12

what will an anterior spinal artery occlusion (infarction) compromises eventually result in?

Answer 12

• spastic paraparesis
• paraplegia (ant. horn damage = LMN)
• bilateral loss of P and T (ALS)
• TVP intact
• urine retention
• sexual dysfunction

Question 13

what is the most likely cause of central medullary syndrome?

Answer 13

syringomyelia

Question 14

what are the symptoms of central medullary syndrome?

Answer 14

• segmented muscle atrophy (usually in hands or fingers)

- loss of T and P

Question 15

define lower motor neurons?

Answer 15

motor neurons that communicate directly with somatic muscle

Question 16

define upper motor neurons?

Answer 16

motor neurons arising form motor centers in the brain that communicate either directly with LMN or indirectly via local interneurons

Question 17

what are pyramidal motor systems?

Answer 17

tracts formed by corticospinal fibers that form with the pyramids of the ventral medulla. (term used interchangebly with corticospinal tracts)

Question 18

define paralysis

Answer 18

complete or almost complete loss of motor function due to a lesion of neurons or muscle

Question 19

what does plegia mean?

Answer 19

paralysis

Question 20

what does paresis mean?

Answer 20

subparalytic muscle weakness

Question 21

what does hemiparesis mean?

Answer 21

partial paralysis of one side of the body

Question 22

define prevalence?

Answer 22

of cases of a disease present in a population at a given time

Question 23

define incidence?

Answer 23

of new cases of a disease occurring during a certain period

Question 24

which motor systems are most clinically important?

Answer 24

coritcospinal and corticobulbar systems

Question 25

where does the lateral corticospinal tract start

Answer 25

pyramidal cells (layer 5) of Brodmann’s area 4 (PreCG)

Question 26

where does the corticobular tract start

Answer 26

pyramidal cells (layer 5) of Brodmann’s area 4 (PreCG)

Question 27

where does the rubrospinal tract start

Answer 27

red nucleus (midbrain)

Question 28

where does the lateral vestibulospinal tract start?

Answer 28

lateral vestibular nucleus (largely pontine)

Question 29

where does the medial vestibulospinal tract start?

Answer 29

medial vestibular nucleus in pons and medulla

Question 30

where does pontine/medial reticulospinal tract start?

Answer 30

oral and causal reticular nuclei in pons

Question 31

where does medullary/ lateral reticulospinal tract start?

Answer 31

gigantocellular reticular nucleus in medulla

Question 32

where do LMN come from?

Answer 32

spinal cord (contribute to spinal n.)
brainstem (contribute to cranial n.)

Question 33

what motor neurons undergo decussation?

Answer 33

UMN

this means many motor centers may control muscles either bilaterally or contralaterally

Question 34

where do the cell bodies of lateral (flexion) motor neurons dwell?

Answer 34

dorsal portion of ventral horn

Question 35

where do the cell bodies of the medial (extension) motor neurons dwell

Answer 35

ventral portion of ventral horn