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Nervous System > Brain control of Movement - Motor control 2 > Flashcards

Brain control of Movement - Motor control 2 Flashcards

1
Q

Where does directional tuning occur?

A

Primary motor cortex (area 4)

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2
Q

What can be said about the neurons in M1 and the direction of movement they control?

A

Each neuron has a preferred direction but the responses of all neurons are combined to produce a population vector

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3
Q

What kind of loop mechanisms control movement?

A

Both feedback and feedforward mechanisms control movement

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4
Q

What are examples of feedback mechanisms in movement?

A

Change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurons to correct postural instability

In addition, before movement begins brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustements to stabilise posture

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5
Q

In damage to descending motor pathways, what does the injury site determine?

A

The symptoms

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6
Q

In terms of movement, what does cortical damage cause?

A

Immediate flaccidity of contralateral muscles:

initial hypotonia due to “spinal shock” where spinal circuits are deprived of cortical input

days later spinal motor reflexes re-emerge in a consistent pattern as spared connections strengthen and new connections sprout

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7
Q

what does actual change in body position initiate?

A

initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability

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8
Q

what do brainstem reticular formation nuclei do before movements are carried out?

A

initiate feedforward anticipatory adjustments to stabilize posture in preparation

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9
Q

what is evidence for anticipatory maintenance of body posture?

A

Hear sound - pull on handle - contracts biceps. BUT - gastrocnemius muscle in leg contracts first to ensure stability

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10
Q

how can a Cat strike with a front paw and not fall over?

A

due to anticipatory feedforward adjustments
- Contralateral front & ipsilateral back legs contract, shift weight to diagonal distribution

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11
Q

where does major subcortical input to area 6 come from?

A

ventral lateral nucleus in dorsal thalamus (VLo)

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12
Q

where does Input to VLo?

A

Input to VLo comes from basal ganglia

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13
Q

what are basal ganglia?

A

Basal ganglia are targets of frontal, prefrontal and parietal cortex

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14
Q

describe the course for basal ganglia motor loop?

A

Cortex 🡪 thalamus & basal ganglia🡪
SMA (cortex area 6)

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15
Q

what does basal ganglia motor loop initiate?

A

willed movements

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16
Q

what are the major components of the basal ganglia?

A

Corpus striatum (“striped body”)

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17
Q

what does the Corpus striatum (“striped body”) include?

A

includes two principal nuclei the caudate and the putamen

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18
Q

what are the caudate and the putamen of corpus striatum known for?

A

input zone of the basal ganglia

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19
Q

where does corpus striatum receive input from?

A

corticostriatal pathway - multiple parallel pathways with different functions

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20
Q

what is the appearance of neurones in putamen and caudate?

A

Medium spiny neurones

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21
Q

what do Medium spiny neurones in putamen and caudate receive?

A

receive excitatory (glutamatergic) cortical inputs on dendrites

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22
Q

describe neurones & circuits of basal ganglia?

A

Large dendritic trees and integrate massive somatosensory, premotor and motor cortical inputs

Each cortical axon contacts 1000s of spiny neurones, so integrating influence of 1000s of cortical cells

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23
Q

describe the axons of the neurons of basal ganglia?

A

Axons are inhibitory (GABAergic). Project to globus pallidus and substantia nigra pars reticulata

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24
Q

where do axons of the basal ganglia fire to?

A

Project to globus pallidus and substantia nigra pars reticulata

25
Q

when does putamen fire?

A

before limb/trunk movements

26
Q

when does caudate fire?

A

before eye movements

27
Q

what do both putamen and caudate do?

A

predict movement

28
Q

what is the motor loop?

A

Cortex → Basal ganglia → Cortex

29
Q

how would you describe the type of pathway between cortex to putamen?

A

excitatory pathway

30
Q

how would you describe the type of pathway between putamen to globus pallidus?

A

inhibitory pathway

31
Q

describe the type of pathway between Globus pallidus to VLo neurones?

A

inhibitory pathway

32
Q

describe the type of pathway between VLo back to SMA?

A

excitatory pathway

33
Q

what is the functional consequence of cortical activation of putamen?

A

excitation

34
Q

what do globus pallidus neurones do at rest?

A

At rest globus pallidus neurones are spontaneously active and inhibit VLo

35
Q

describe cortical excitation?

A

Excites putamen, which
Inhibits (inhibitory) globus pallidus, which therefore
Reduces inhibition of VLo cells, so
Activity in VLo boosts SMA activity

Positive feedback loop for focussing or funnelling activation of widespread cortical areas back onto cortical SMA

36
Q

what does ‘Gating’ by basal ganglia depend on?

A

disinhibitory arrangement

37
Q

describe the direct pathway through basal ganglia?

A

positive feedback loop, a “GO” signal to the SMA in cortex

Enhances initiation of movements by the SMA

Globus pallidus neurones are spontaneously active at rest, so tonically inhibit (restrain) VL thalamus

input from the cortex releases this inhibition

38
Q

describe the indirect pathway through basal ganglia?

A

Striatum inhibits GPe (globus pallidus, external) which then inhibits both GPi (GP, internal) & STN (subthalamic nuclei)

Cortex excites STN; this excites Gpi; which inhibits thalamus

39
Q

action of direct pathway?

A

Direct pathway - selects specific motor actions

40
Q

action indirect pathway?

A

Indirect pathway - suppresses other/inappropriate action

41
Q

what are some disorders of the basal ganglia?

A

Parkinson’s disease

42
Q

who does parkinsons disease affect?

A

affects 1% over 60 years

43
Q

what is hypokinesia?

A

slowness, difficult to make voluntary movements, increased muscle tone (rigidity), tremors of hand and jaw.

44
Q

what is the cause of parkinsons disease?

A

degeneration of neurones in substantia nigra (SN), so loss of their dopaminergic (excitatory) inputs to the striatum

45
Q

what is the function of dopamine?

A

(normally) enhances cortical inputs through the “direct” pathway and suppress inputs through “indirect” pathway

46
Q

what results from depletion of dopamine?

A

(Parkinson’s) closes down focussed motor activities that funnel through thalamus to SMA

47
Q

what is huntingtons disease?

A

Hyperkinesia with dementia and personality disorders

48
Q

is huntingtons disease hereditary?

A

rare (5-10/100,000) progressive and fatal

49
Q

what is a characteristic symptoms of huntingtons disease?

A

Characteristic chorea – spontaneous, uncontrolled, rapid flicks and major movements with no purpose

50
Q

what is the cause of huntingtons disease?

A

Cause - profound loss of caudate, putamen and globus pallidus

i.e. loss of ongoing (tonic) inhibition by basal ganglia

51
Q

how much of brain volume does the cerebellum take up?

A

only 10% of brain volume, but
- 50% of total CNS neurones

52
Q

what is the involvement of cerebellum in movement?

A

‘Commanding’ a contraction is not enough - skilled movements need detailed sequence of timed contractions of varied intensity and duration

53
Q

what do lesions in cerebellum result in?

A

uncoordinated, inaccurate movements = ataxia:
- e.g. fail to touch nose with eyes shut (similar to alcohol which depresses cerebellar circuits)

54
Q

what are M1 Layer 5, areas 4 & 6, somatosensory cortex all are part of?

A

HUGE cortico-ponto-cerebellar projection (connects cortex, pontine nuclei & cerebellum) - 20 mill axons (20x more than CST)

55
Q

what does cerebellum instruct?

A

cerebellum instructs direction, timing and force

56
Q

describe the motor loop through lateral cerebellum?

A
57
Q

what are Brain-machine interfaces (BMI)?

A

BMI - allow patients to voluntarily control prosthetic limbs and walk again following spinal cord injuries

Sensory properties are being built into prosthetic limbs, so patients can get sensory feedback when their prosthetic limb makes contact with objects or people.

58
Q

what are brain-brain interfaces (BBI)?

A

BBI - use brain signals from one animal to teach another animal a task it has never seen.

Nervous System (40 decks)

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