Motor Control (Intro)

Question 1

what controls posture and balance?

Answer 1

brainstem nuclei (by controlling and integrating spinal reflexes into higher order reflexes)

Question 2

from what do brainstem nuclei receive input?

Answer 2

higher brain centres:
> cerebral cortex
> basal ganglia
> cerebellum

Question 3

what four systems control muscle movement?

Answer 3

> descending control pathways
basal ganglia
cerebellum
local spinal cord and brainstem circuits

Question 4

a lesion in which motor neuron would cause flaccid paralysis and muscle atrophy?

Answer 4

lower motor neurons

Question 5

lesions in which motor neurons would cause spasticity and some paralysis, which may be transient?

Answer 5

upper motor neurons

Question 6

what do lesions in posture regulating pathways cause?

Answer 6

spastic paralysis

Question 7

what will corticospinal lesions cause?

Answer 7

weakness

Question 8

where are proximal shoulder muscle mapped to?

Answer 8

medial motorneurones

Question 9

where are finger muscles mapped to?

Answer 9

lateral motorneurones

Question 10

how does the spinal cord receive descending input?

Answer 10

via neurons in the brainstem

Question 11

how does the spinal cord receive direct cortical input?

Answer 11

via corticospinal/pyramidal tract

Question 12

at what levels does sensory input enter the spinal cord?

Answer 12

at all levels

Question 13

in the brainstem what does the vestibular system inform about?

Answer 13

balance

Question 14

what is the effect of damaged sensory inputs?

Answer 14

paralysis similar to if the motor neurones themselves have been damaged

Question 15

describe the stretch reflex

Answer 15

the muscle spindle is stretched and the action potential is fired synapsing in the spinal cord on an excitatory motor neuron which will innervate the same muscle.
at the same time the sensory neuron synapses on an interneuron which releases inhibitory neurotransmitter quieting any action potential of the alphamotor neuron supplying the antagonist muscle (flexor)

Question 16

what spinal cord segment is tested in bicep reflex?

Answer 16

C6

Question 17

what spinal cord segment is tested in tricep reflex?

Answer 17

c7

Question 18

what spinal cord segment is tested in patellar tendon reflex?

Answer 18

L4

Question 19

what spinal cord segment is tested in Achilles tendon reflex?

Answer 19

s1

Question 20

is the flexor/withdrawal reflex monosynaptic and protective?

Answer 20

no it is polysynaptic and protective

Question 21

describe the limb is withdrawn in the flexor/withdrawal reflex

Answer 21

increased activity in the flexor muscles of the affected part via a number of excitatory interneurons.
at the same time through excitatory and inhibitory interneurons the antagonistic extensors are inhibited.

Question 22

what is the effect of the branching of the sensory neuron carrying pain in the flexor withdrawal reflex?

Answer 22

interneurons in several spinal segments are activated which in turn activate alpha motor neurones controlling all the flexor muscles of the affected limb

Question 23

describe how the contralateral limb extends in the flexor withdrawal reflex

Answer 23

> excitatory interneurons cross the spinal cord and excite the contralateral extensors
via interneurons there is inhibition of the contralateral flexors
sensory information ascends the brain in the contralateral spinothalamic tract to help maintain upright posture

Question 24

which is slower the stretch reflex or the flexor reflex?

Answer 24

the flexor reflex

Question 25

how are reflexes overridden voluntarily?

Answer 25

descending voluntary excitation of alpha motorneurones can override the inhibition from the GTOs and maintain contraction

Question 26

what is the effect on muscles of high gamma motorneurone activation of muscles spindles?

Answer 26

muscles become extremely resistant to stretch and are spastic

Question 27

what does the activation of gamma motor neurons depend on?

Answer 27

descending pathways

Question 28

what is facilitation?

Answer 28

increased effects due to an increased sensory input

Question 29

how do pain fibres facilitate the action of muscle spindles?

Answer 29

by maintaining the aloha motor neurons in a more depolarised state.

Question 30

what is babinski’s sign?

Answer 30

extension and not flexion of the toes when stimulating the lateral aspect of the sole due to damage or disruption of the CS tract

Question 31

are reflexes seen in limbs after spinal shock?

Answer 31

yes after a period of time there is a gradual return of reflexes which are exaggerated. (clonus) though there limbs are still functionally useless.