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6. Neurology (Med) > Motor Control 2 > Flashcards

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 is the Babinski sign?

A

Stimulation of lateral plantar aspect of foot leads to extension of the big toe, there may also be fanning of the other toes

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8
Q

What is supposed to occur with stimulation of the lateral plantar aspect of the foot in adults?

A

Planter flexion

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9
Q

When does planter extension occur on stimulation to the lateral planter aspect of the foot?

A

In baby or with cortical damage

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10
Q

What are examples of things that damage to descending motor pathways causes?

A

Flaccidity of contralateral muscles

Babinski sign (tendon reflexes impacted)

Loss of fine finger movement

Spasticity (due to removal of cortical suppressive influences)

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11
Q

What does the basal ganglia motor loop do?

A

Selects and initiates willed movements

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12
Q

What does Vlo stand for?

A

Ventral lateral nucleus in dorsal thalamus

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13
Q

Where does major subcortical input to area 6 comes from?

A

Ventral lateral nucleus in dorsal thalamus

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14
Q

Where does input to Vlo come from?

A

Basal ganglia

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15
Q

Where does input to the basal ganglia come from?

A

Frontal, prefrontal and parietal cortex

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16
Q

Explain the process of the basal ganglia motor loop?

A

Cortex > thalamus and basal ganglia > back to the SMA in cortex (area 6)

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17
Q

What are some major components of the basal ganglia?

A

Corpus striatum (stripped body)

This includes two principal nuclei, the caudate and the putamen

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18
Q

What are the input zones for the basal ganglia, and where do they recieve input from?

A

Caudate and putamen

From all over the cortex

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19
Q

What kind of inputs does the medium spiny neurons of the putamen and caudate receive?

A

Excitatory (glutamatergic) cortical inputs on dendrites

they have large dendritic trees and integrate massive somatosensory, premotor and motor cortical inputs

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20
Q

Are the axons of the putamen and caudate excitatory or inhibitory?

A

Inhibitory (GABAergic)

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21
Q

Where does the putamen and caudate project to?

A

Globus pallidus and to substantia nigra pars reticulata

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22
Q

What does the putamen fire before?

A

Limb/trunk movements

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23
Q

What does the caudate fire before?

A

Eye movements

24
Q

The motor loop is cortex > basal ganglia > cortex, which of these pathways are excitatory and which are inhibitory?

A

Cortex to putamen - excitatory

Putamen to globus pallidus - inhibitory

Globus pallidus to VLo neurons - inhibitory

VLo back to SMA - excitatory

this means functional consequence of cortical activation of putamen is excitation

25
Q

Explain how cortical activation of putamen boosts cortical excitation?

A

At rest, globus pallidus neurons are spontaneously active and inhibit VLo

So cortical excitation:

1) Excites putamen which
2) Inhibits the inhibitory globus pallidus which
3) Releases cells in VLo from inhibition so
4) Activity in VLo boosts SMA activity

26
Q

At rest, what state are neurons in the globus pallidus?

A

Spontaneously active and inhibit VLo

27
Q

What kind of loop does the motor loop of the basal ganglia act as?

A

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

28
Q

When does the “go” signal for voluntary movement occur?

A

When the SMA is boosted beyong threshold level by activity coming through the basal ganglia funnel

29
Q

What kinds of loops do cortical inputs flow as through basal ganglia (2 different kinds)?

A

Direct pathway

Indirect pathway

30
Q

What is the function of direct pathway through basal ganglia?

A

Acts as positive feedback loop causes a “go” signal to the SMA in cortex

Enhances the initiation of movements by the SMA

31
Q

What is the function of the indirect pathway through the basal ganglia?

A

Antagonises the direct root

Inhibits the thalamus, suppreses competing/inappropriate action

32
Q

What is the process of the indirect pathway through the basal ganglia?

A

1) Striatum inhibits GPe (globus pallidus external)
2) This inhibits both GPi (GP internal) and STN (subthalamic nuclei)
3) Cortex excites STN, this excites GPi which inhibits thalamus

33
Q

What are examples of basal ganglia disorders?

A

Parkinson disease (PD)

Huntington disease

34
Q

What does GPe stand for?

A

Globus pallidus external

35
Q

What does GPi stand for?

A

Globus pallidus internal

36
Q

What does STN stand for?

A

Subthalamic nuclei

37
Q

What causes parkinson disease?

A

Degeneration of neurons in substantia nigra (SN) and their dopaminergic (excitatory) inputs to the striatum

Depletion of dopamine closes down the activation of the focussed motor activites that funnel through thalamus to SMA

38
Q

What does SN stand for?

A

Substantia nigra

39
Q

Are dopaminergic inputs excitatory or inhibitory?

A

Excitatory

40
Q

Are GABAergenic inputs excitatory or inhibitory?

A

Inhibitory

41
Q

How does dopamine impact the direct and indirect pathways through the basal ganglia?

A

Enhances cortical inputs through direct pathway

Suppresses inputes through the indirect pathway

42
Q

What is a major symptom of PD?

A

Hypokinesia

43
Q

What does hypokinesia describe?

A

Slowness

Difficult to make voluntary movements

Increased muscle tone (rigidity)

Tremors of hand and jaw

44
Q

What is Huntington’s disease?

A

Hyperkinesia with dementia and personality disorders

Progressive and fatal

Hereditary

45
Q

What is the prevalence of Huntington’s disease?

A

5-10/100,000

46
Q

What is Huntington’s disease caused by?

A

Profound loss of caudate, putamen and globus pallidus

So loss of ongoing inhibitory effects of basal ganglia

47
Q

Huntington’s disease shows characteristic chorea, what does this describe?

A

Spontaneous, uncontrolled, rapid flicks and major movements with no purpose

48
Q

What percent of brain volume is the cerebellum?

A

10%

49
Q

What percentage of CNS neurons are in the cerebellum?

A

50%

50
Q

What do lesions to the cerebellum cause?

A

Uncoordinated inaccurate movements:

ataxia

fail to touch nose with eyes shut

similar to alcohol which represses cerebellar circuits

51
Q

What is ataxia?

A

A term for a group of disorders that affect co-ordination, balance and speech

52
Q

What connects the cortex, pontine nuclei and cerebellum?

A

Cortico-ponto-cerebellar projection

53
Q

What parts of the cortex are part of the cortico-ponto-cerebellar projection?

A

Layer 5

Areas 4 and 6

Somatosensory cortex

54
Q

What does information travel from the cerebellum back to the cortex via?

A

Ventrolateral thalamus

55
Q

What information does the cerebellum give the cortex?

A

Instructs direction, timing and force required to coordinate movement

56
Q

What does the motor loop for voluntary movement through basal ganglia and VLo undergo ongoing refinement from?

A

Involvement of feedback loop through pons, cerebellum, thalamus and back to cortex

6. Neurology (Med) (47 decks)

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