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neurology > motor control 1 > Flashcards

motor control 1 Flashcards

1
Q

what are the 3 levels of motor control hierarchy?

A

high
middle
low

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2
Q

what are the structures associated with high motor control?

A

association neocortex

basal ganglia

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3
Q

what are the structures associated with middle motor control?

A

motor cortex

cerebellum

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4
Q

what are the structures associated with low motor control?

A

brainstem

spinal cord

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5
Q

what do the lateral pathways of the spinal cord control?

A

voluntary movements of distal muscles - under direct cortical control

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6
Q

what do ventromedial pathways control?

A

posture and locomotion - under brain stem control

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7
Q

where does the corticospinal tract decussate?

A

medulla/spinal cord junction

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8
Q

how do CST axons control muscles?

A

they synapse on ventral horn motor neurones and interneurons

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9
Q

where does 2/3ds of the CST originate?

A

areas 4 and 6 of the frontal motor cortex - rest is somatosensory

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10
Q

where does the rubrospinal tract originate?

A

red nucleus of the midbrain

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11
Q

what happens if there are lesions in the CST and RST?

A

fine movements of the arms and hands lost.

unable to move shoulders, elbows, wrist and fingers independently

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12
Q

what happens if there is a lesion in the CST but not the RST?

A

fine movements initially lost but after a few months functions reapper because the RST takes over

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13
Q

what does the vestibulospinal tract do?

A

stabilizes head and neck

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14
Q

what does the tetospinal tract do?

A

ensures eyes remain stable as body moves

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15
Q

where do the pontine and medullary reticulospinal tracts originate?

A

brainstem

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16
Q

what sensory information do the pontine and medullary Reticulospinal tracts use?

A

balance
body position
vision

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17
Q

what is the function of the pontine and medullary reticulospinal tracts?

A

reflexly maintain balance and body position

innervate trunk and antigravity muscles in limbs

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18
Q

what does the motor cortex do when complex movement is required?

A

directly activates spinal motoneurones and frees them from reflex control by communicating via nuclei of ventromedial pathways

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19
Q

where do the medial tracts of white matter originate?

A

brainstem

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20
Q

where do the lateral tracts of white matter develop?

A

cortex

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21
Q

where in the brain is the primary motor cortex?

A

precentral gyrus

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22
Q

what does the cerebral cortex need to know in order to plan movement?

A

where the body is in space
where it wants to go
needs to select a plan to get there

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23
Q

what is the function of the supplementary motor area?

A

innervates distal motor units directly

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24
Q

what is the function of the premotor area?

A

connects reticulospinal neurones innervating proximal motor units

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25
Q

why is area 6 of the brain sometimes described as a “junction”?

A

it is where signals encoding what actions are desired are converted into how the actions will be carried out

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26
Q

what happens with regard to blood flow to the brain during practised voluntary finger movements?

A 
blood flow increases in the following areas:
somatosensory
posterior parietal
prefrontal cortex
areas 6 and 4
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27
Q

if you were to “think” about making a movement, which area would be active?

A

area 6 but not area 4- area 4 is for “doing it”

28
Q

what are the decision making neurones in command centres?

A

neurones in the premotor area

29
Q

when are neurones in area 6 fired?

A

during movement
when movement is imagined
when you see others making a specific movement

30
Q

how is the direction of movement decided?

A

neurone discharge is greatest in a preferred direction
each neurone has a preferred direction but responses of all neurons are combined to produce a population vector
overall movement direction is encoded by the integrated activity of all neurones

31
Q

what does a change in body position initiate in regard to feedback?

A

messages from brainstem vestiblar nuclei to spinal cord motor neurones to correct postural instability

32
Q

what must happen before movements to change body position start?

A

brainstem reticular formation nuclei (controlled by the cortex) initiate feed forward anticipatory adjustments to stabilize posture

33
Q

what does cortical damage cause?

A

immediate flaccidity of contralateral muscle

34
Q

what causes initial hypotonia?

A

spinal circuits being derived of cortical input

35
Q

how do spinal circuits manage to regain their function in spinal shock?

A

days later, spared connections strengthen and new connection sprout - consistent pattern of motor signs emerges

36
Q

what does the babinski sign indicate?

A

incomplete upper control of spinal circuits

37
Q

what results in spasticity?

A

removal of cortical suppressive influences

38
Q

where does the major subcortical input to area 6 of the brain come from?

A

ventral lateral nucleus in dorsal thalamus

39
Q

what is the basal ganglia motor loop?

A

information cycles from the cortex through the thalamus and basal ganglia, then back to the SMA in cortex

40
Q

what are the major components of basal ganglia?

A

corpus striatum

41
Q

what is the input zone of the basal ganglia?

A

caudate

putamen

42
Q

where does the corpus striatum receive input from?

A

all over the cortex; the corticostriatal pathway is made up of multiple parallel pathways with different functions

43
Q

where are medium spiny neurones located?

A

putamen and caudate

44
Q

what kind of signals do medium spiny neurones receive on their dendrites?

A

excitatory cortical inputs

45
Q

what kind of inputs do medium spiny neurones integrate?

A

somatosensory
premotor
motor cortical

46
Q

where do the axons of medium spiny neurones project to?

A

globus pallidus
substantia nigra
pars reticula

47
Q

when do the neurones of the putamen fire?

A

before limb/trunk movements

48
Q

when do the neurones of the caudate fire?

A

before eye movements

49
Q

what is the functional consequence of cortical activation of the putamen?

A

excitation

50
Q

how does cortical activation of the putamen result in an excitatory signal being sent to the SMA?

A

putamen sends inhib signal to globus pallidus
globus pallidus sends inhib signal to VLo
VLo then sends excitatory signal to the SMA

51
Q

what do globus pallidus neurones do at rest?

A

inhibit the VL signal

52
Q

what is the effect of inhibiting the globus pallidus?

A

releases cells in VLo from inhibition so activity in VLo boosts SMA activity

53
Q

how does the indirect basal ganglia loop work?

A

antagonizes the direct route:

striatum inhibits globus pallidus externa which then inhibits the GPi and the subthalamic nuclei

54
Q

what effect does exciting the subthalamic nuclei have

A

excites GPi which inhibits thalamus

55
Q

what is the function of the indirect pathway

A

suppresses competing/inappropriate action to the movement initiated by the direct pathway

56
Q

what is hypokinesia and what is it a sign of?

A

slowness
difficulty making voluntary movements
increased muscle tone (rigidity)
tremors of hand and jaw

57
Q

what is the pathology of parkinsons disease?

A

degeneration of neurones in the substantia nigra and their dopaminergic (excitatory) inputs to the striatum

58
Q

what is the effect of dopamine in the basal ganglia pathway?

A

can enhance cortical inputs through the direct pathway and suppress inputs through the indirect pathway?

59
Q

what is the effect of depletion of dopamine?

A

closes down activation of the focussed motor activities that funnel through the thalamus to the SMA

60
Q

what is huntingtons disease caused by?

A

profound loss of caudate, putamen and globus pallidus - therefore loss of the ongoing inhibitory effects of the basal ganglia

61
Q

what percentage of CNS neurones does the cerebellum contain?

A

50 percent

62
Q

what do lesions of the cerebellum produce?

A

uncoordinated, inaccurate movements

63
Q

what parts of movement does the cerebellum instruct?

A

direction
timing
force

64
Q

how is the cerebellum linked back to the cortex?

A

ventrolateral thalamus

65
Q

how does the motor loop for voluntary movement undergo refinement?

A

via involvement of a feedback loop through the pons, cerebellum, thalamus and then back to the cortex

neurology (29 decks)

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