Descending motor systems

Question 1

what part of the brain does the descending upper motor neuron travel through to get to the brain stem

Answer 1

internal capsule of white matter

Question 2

what is the function of lower motor neurons

Answer 2

directly signals and innervate muscle to contract

Question 3

what is the function of upper motor neurons

Answer 3

send signal from the motor cortex to the lower motor neuron down an axon

Question 4

what would be the results of a lesion in a lower motor neuron

Answer 4

• atonia
• areflexia (loss of knee reflex)
• flaccid paralysis
• fasiculations (twitching)
• severe atrophy

Question 5

what would be the result of a lesion in an upper motor neuron

Answer 5

• spastic paralysis
• hypertonia
• hyperflexia
• mild atrophy
• pathologic reflexes (Babinski sign)

Question 6

what is the Babinski sign and what causes it ?

Answer 6

big toe dorsoflexion w/fanning of other toes when side of heel it stroked, cause by upper motor neuron lesion

Question 7

what horn would you find motor neuron cell bodies

Answer 7

anterior horn/ventral horn

Question 8

what horn would you find somatosensory cell bodies

Answer 8

posterior horn/dorsal horn

Question 9

nuerons controlling axial muscles tend to stay ____ and those controlling distal muscles tend to stay _____ in the anterior horn

Answer 9

medial, lateral

Question 10

neurons controlling flexor mm. are located ______ to the extensor muscle neurons in the anterior horn

Answer 10

posterior

Question 11

what is a motor unit ?

Answer 11

1 motor neuron + all myofibers it innervates

Question 12

which type of muscle (small or large) demonstrates a very small amount of myofibers innervated by 1 motor unit

Answer 12

small ( extraoccular m. has fine movement so must have small number of myofiber innervated by 1 motor unit)

Question 13

functionally what are the 3 types of muscle fibers

Answer 13

standing, running, walking

Question 14

What are the characteristics of type 1 muscle fibers and what is its function

Answer 14

slow twitch, high lipids low sugar, red oxidative (lots of mitochondria)

• used for standing
• dark meat

Question 15

what are the characteristics of type 2 muscle fibers and what is its function

Answer 15

fast twitch, low lipids high sugar, white glycolytic (little mitochondria

• used for running and jumping
• white meat

Question 16

what are the 3 regions of the brain that influence (plan/monitor) upper motor neuron output but have NO direct effect on lower motor neurons

Answer 16

basal ganglia
association cortex
cerebellum

Question 17

what is the difference b/w hierarchial motor control and parallel motor control

Answer 17

Hierarchial - premotor cortex tells motor cortex and the LMN what to do
Parallel - premotor cortex directly talks to LMN what to do

Question 18

motor nuerons are found on the _____ horn, but terminate or synapse on the _____ horn

Answer 18

anterior/ventral horn

posterior/dorsal horn

Question 19

what are the 3 main descending motor pathways

Answer 19

• corticospinal tract
• corticobulbar tract
• corticopontine tract

Question 20

where is the primary motor cortex

Answer 20

precentral gyrus (area 4)

Question 21

where is the primary somatosensory cortex

Answer 21

postcentral gyrus (3,1,2)

Question 22

T/F the corticospinal tract originates in the primary motor area only ?

Answer 22

False, originates in the primary motor area, somatosensory area, premotor area, supp. motor area, and superior parietal lobule

Question 23

what does the primary motor area control

Answer 23

contralateral, voluntary fine digital movements

Question 24

where is the premotor area and what does it control

Answer 24

lateral aspect of area 6

-plans movements/gives instructions to motor cortex in response to an external stimulus

Question 25

what would a lesion in the primary motor area cause

Answer 25

complete paralysis of contralateral musculature

Question 26

what would a lesion in the premotor area cause

Answer 26

- moderate weakness of contralateral musculature | - loss ability to associate hand movements to visual or verbal cues

Question 27

where is the supplemental motor area and what is its function

Answer 27

medial aspect of area 6 (premotor area is lateral) | -plans movements while thinking, "imagines/visualizes" movements

Question 28

though the corticospinal tract is a "complex tract", what movement would be permanently loss if you were to cut it

Answer 28

fine finger movement

Question 29

where does the corticospinal tract decussate at ?

Answer 29

spinomedullary junction (85 %)

Question 30

85 % of the lateral corticospinal tract decussates at the spinomedullary junction and descends to where ?

Answer 30

lateral funiculus

Question 31

the anterior corticospinal tract that does NOT decussate (15%) descends to _________ and controls what muscle activity

Answer 31

anterior funiculus | -axial muscle activity

Question 32

a lesion in the corticospinal tract in the brain would cause what type of muscle weakness ipsilateral or contralateral

Answer 32

contralateral cuz it decussates at spinomedullary junction

Question 33

what does the rubrospinal tract control

Answer 33

shoulder and proximal arm mm

Question 34

what does the reticulospinal tract control

Answer 34

rhythmic motor actions like walking

Question 35

what does the vestibulospinal tract control

Answer 35

balance (why cats land on feet)

Question 36

what does the tectospinal tract control

Answer 36

head turning

Question 37

the corticobulbar pathway ends on what CN nuclei, and specifically what CN recieve no input

Answer 37

V, VII, X, XI, XII | No input - III, IV, VI (all eye muscles)

Question 38

the corticobulbar path has what type of decussation and what type of input ?

Answer 38

Has No decussation so bilateral input

Question 39

what CN is the exception to the typical corticobulbar pathway

Answer 39

CN V - upper face innervate bilaterally - BUT lower face (lips) innervated ipsilaterally

Question 40

unilateral damage to CN V of the corticobulbar pathway would result in ?

Answer 40

-inability to smile symmetrically (only lower facial muscles affected cuz upper face can still recieve input from other side since its inervated bilaterally)