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Systems: Neurology AB > Motor Control 2 > Flashcards

Motor Control 2 Flashcards

1
Q

Overall movement direction is encoded by?

A

The integrated activity of all the neurones

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2
Q

What type of mechanisms control movement?

A

Feedback and feedforward

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3
Q

What role does feedback play in the control of movement?

A

A change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability

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4
Q

What role does feedforward play in the control of movement?

A

Before movements begin, brainstem reticular formation nuclei (controlled by the cortex) initiate feedforward anticipatory adjustments to stabilize posture

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5
Q

What determines the symptoms of an UMN lesion?

A

Injury site

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6
Q

What does cortical damage cause?

A

Immediate flaccidity of contralateral muscles.

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7
Q

What is normal Babinksi sign?

A

Plantar flexion

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8
Q

What Babinskin sign would be seen in babies and those with cortical damage?

A

Plantar extension

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9
Q

What are the signs of UMN syndrome?

A
  • Flaccidity
  • Hypotonia
  • Babinksi sign
  • Spasticity
  • Loss of fine finger movements
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10
Q

What spasticity can be seen in the UMN syndrome?

A
  • Increased muscle tone
  • Hyperactive stretch reflex
  • Clonus oscillatory contract/relax muscles in response to stretch- due to removal of cortical suppressive influences
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11
Q

What do basal ganglia motor loops do?

A

Selects an initiates willed movements

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12
Q

Where does major subcorctical input to area 6 come from?

A

Ventral lateral nucleus in dorsal thalamus

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13
Q

What is input to area 6 known as?

A

VLo and arises from basal ganglia

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14
Q

What is the basal ganglia targets of?

A

Frontal, prefrontal and parietal cortex

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15
Q

What is the loop of information cycles?

A

Cortex through thalamus and basal ganglia back to SMA in cortex

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16
Q

What are the major components of the basal ganglia?

A
  • Corpus striatum (striped body) - includes two principal nuclei the caudate and the putamen
  • They are the input zone of the basal ganglia
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17
Q

Where does the corpus striatum receive input from?

A

All over the cortex

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18
Q

What are the corticostriatal pathways?

A

Multiple parallel pathways with different functions

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19
Q

What fires before limb/trunk movements?

A

Putamen

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20
Q

What fires before eye movements?

A

Caudate

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21
Q

What in the putamen and caudate receive excitatory (glutamatergic) cortical inputs on dendrites?

A

Medium spiny neurones

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22
Q

What do the medium spiny neurones have?

A
  • They have large dendritic trees and integrate somatosensory, premotor and motor cortical inputs
  • Each cortical axon contacts 1000s of spiny neurones so integrating the influence of 1000s of cortical cells
  • Their axons are inhibitory (GABAergic) and project to globus pallidus and to substantia nigra pars reticulata
23
Q

Motor Loop: Cortex to putamen

A

Excitatory

24
Q

Motor Loop: putamen to globus pallidus

A

Inhibitory

25
Q

Motor Loop: globus pallidus to VLo neurones

A

Inhibitory

26
Q

Motor Loop: VLo to SMA

A

Excitatory

27
Q

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

A

Excitation

28
Q

What are the globus pallidus neurones at rest?

A

At rest globus pallidus neurones are spontaneously active and inhibit VL

29
Q

Why does cortical activation of the putamen boost cortical excitation?

A
  • Cortical excitation excites the putamen
  • This inhibits the inhibitory Globus pallidus which therefore
  • Releases cells in VLo from inhibition so
  • Activity in VLo boosts SMA activity
  • Acts as a positive feedback loop focussing or funnelling activation of widespread cortical areas onto cortical SMA
30
Q

When may the go signal for voluntary movement occur?

A

May occur when the SMA is boosted beyond a threshold level by activity coming through the basal ganglia funnel

31
Q

What type of arrangement does the gating operation of the basal ganglia depend on?

A

A chain of neurones arranged in a disinhibitory circuit

32
Q

How does cortical input flow through the basal ganglia?

A

By direct and indirect loops

33
Q

How does cortical input flow by direct loop through the basal ganglia?

A

-Direct pathway acts as a positive feedback loop, a “GO” signal to the SMA in cortex
-It enhances the initiation of movements by the SMA
-Globus pallidus neurones are spontaneously active at rest so they tonically inhibit (restrain) VL thalamus
-Input from cortex releases this inhibition
(Direct pathway slects specific motor actions)

34
Q

How does cortical input flow by indirect loop through the basal ganglia?

A

-Indirect pathway – antagonizes the direct route
-Striatum inhibits GPe (globus pallidus external) which then inhibits both GPi (GPinternal) and STN (subthalamic nuclei)
-Cortex excites STN; this excites Gpi; which inhibits thalamus
(Indirect pathway suppress competing/inappropriate action)

35
Q

Give examples of basal ganglia disorders.

A
  • Parkinson’s

- Huntington’s chorea

36
Q

Who does Parkinson’s affect?

A

1% of the over 60s

37
Q

What is Parkinson’s caused by?

A

Caused by degeneration of neurones in substrantia nigra (SN) and their dopaminergic (excitatory) inputs to the striatum

38
Q

How can dopamine enhance cortical inputs?

A

Through the direct pathway

39
Q

How can dopamine suppress cortical inputs?

A

Through the indirect pathway

40
Q

What does the depletion of dopamine do?

A

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

41
Q

What is Parkinson’s characterised by?

A

Hypokinesia

42
Q

What is hypokinesia?

A
  • Slowness
  • Difficult to make voluntary movements
  • Increased muscle tone (rigidity)
  • Tremors of hand and jaw
43
Q

What is Huntington’s characterised by?

A

Characteristic chorea

44
Q

Who does Huntington’s affect?

A

It is hereditary, rare 5-10/100,000, progressive and fatal

45
Q

What does Huntington’s involve?

A

Involves hyperkinesia with dementia and personality disorders

46
Q

What is Huntington’s caused by?

A

Caused by profound loss of caudate, putamen and globus pallidus so loss of the ongoing inhibitory effects of the basal ganglia

47
Q

What is characteristic chorea?

A

Spontaneous uncontrolled rapid flicks and major movements with no purpose

48
Q

How much of the brain volume is accounted for by cerebellum?

A

10% of brain volume but 50% of total CNS neurones

49
Q

What do lesions to the cerebellum produce?

A

Uncoordinated inaccurate movements , ataxia, fail to touch nose with eyes shut (similar to alcohol which depresses cerebellar circuits)

50
Q

What are part of the HUGE cortico-ponto cerebellar projection?

A

Layer 5, areas 4 & 6, somatosensory cortex

51
Q

What does the cortico-ponto-cerebellar projection do?

A

Connects cortex, pontine nuclei and cerebellum - 20 mill axons, 20x more that CST

52
Q

How is the cerebellum connected to the cortex?

A

Via the ventrolateral thalamus

53
Q

What does the cerebellum instruct n terms of movement?

A

Direction, timing and force

54
Q

Describe the motor loop through the lateral cerebellum.

A

Motor loop for voluntary movement through basal ganglia and VLo undergoes ongoing refinement via involvement of feedback loop through pons, cerebellum, thalamus and back to cortex

Systems: Neurology AB (51 decks)

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