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NAB > Motor systems > Flashcards

Motor systems Flashcards

1
Q

Damage to motor neurons

A

Flaccid paralysis

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2
Q

Damage to primary motor cortex

A

Spastic paralysis with exaggerated spinal reflexes

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3
Q

Damage to brainstem pathways

A

Postural defects and problems with walking

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4
Q

Damage to higher cortical areas

A

Apraxia: movements aren’t ordered or appropriate to the situation

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5
Q

Damage to the cerebellum

A

Ataxia: poorly coordinated movements that may be the wrong size or shape

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6
Q

Damage to the basal ganglia

A

Hyper/hypokinesia since BG involved in action selection

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7
Q

Problems with negative feedback

A

Biological delays, so signal continues while correction starts
-> Over correction and oscillation around a set point

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8
Q

Slow fibre properties

A

Anatomical: few fibres/unit, small
Biochem: oxidative, high myoglobin
Physiological: slow twitch, low tension, fatigue resistant, slow axons

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9
Q

Fast fibre properties

A

Anatomical: large, lots of fibres/motor unit
Biochem: glycolytic, little myoglobin
Physiological: fast twitch, high tension, fast axons, fatiguable

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10
Q

Size principal of motoneuron recruitment

A

Low force units, the slow fibres, are active at low rates of stimulation
As force increases, get recruitment of higher force units
This means the increase in force is via the smallest increments possible to give smooth contraction

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11
Q

How does size principal of motoneuron recruitment come about

A

Lowest threshold motoneurons innervate few fibres and induce them to become slow, low force, fatigue resistant
Higher threshold motoneurons innervate more fibres, inducing them to become fast, fatiguable fibres

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12
Q

Muscle spindle afferents

A

Signal passive stretch

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13
Q

Tendon organ afferents

A

Signal tension, including active tension from muscle contraction
(as well as due to bones being pulled apart with passive stretch)

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14
Q

Bag fibres

A

Central region full of nuclei with no striations

Signal changes in length very well, mainly via primary spindle afferents

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15
Q

Chain fibres

A

Nuclei and striations throughout so stretch acts equally along fibre
Signal static length via secondary spindle afferents mainly

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16
Q

Gamma motoneurons

A

Innervate the ends of intrafusal fibres to make them contract to alter sensitivity of the spindles; so they have similar sensitivity despite changes in starting length of the spindle

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17
Q

Problems with stretch reflex proposal

A

Gain is measured to be less than 1 so can’t be a fully compensatory contraction for unexpected loads

Delays due to negative feedback would lead to muscle oscillation

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18
Q

Spasticity

A

Due to damage to descending pathways

  • Exaggerated high gain stretch reflex
  • Brisk response to tendon tapping and oscillating contraction; myoclonus
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19
Q

When are gamma motoneurons very active

A

During slow high gain reflexes such as walking on a beam

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20
Q

Reciprocal inhibition

reflex inhibition accompanying stretch reflex

A

Primary spindle afferents innervating inhibitory motoneurons off antagonistic muscles to prevent them working against the other contraction

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21
Q

Recurrent inhibition

reflex inhibition accompanying stretch reflex

A

Via Renshaw cells
Primary spindle afferents activate inhibitory interneurons of the same motoneuron pool (renshaw cells); type of negative feedback to prevent jerkiness and tremor

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22
Q

Tendon organ context dependent reflexes

A

Tendon afferents can activate alternate pathways depending on context e.g when walking compared to at rest

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23
Q

Infant specific reflexes

A

Babinski’s sign/plantar reflex
Grasp reflex
Reflex stepping

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24
Q

Central pattern generators

A

Intrinsic circuit within spinal cord to simplify a patterned movement e.g walking; just need brain input to start and stop

Most vertebrates have spinally generated locomotion but humans have lost this (except reflex stepping)

All have CPG in brainstem for breathing

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25
Q

Reticulospinal pathway

A

Ventromedial
From reticular formation
Drives spinal motor control, activating CPGs and whole body stereotypical actions

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26
Q

Vestibulospinal pathway

A

Ventromedial
From vestibular nuclei
For balance and anti-gravity extensor action

27
Q

Tectospinal pathway

A

Ventromedial
From rostral/superior colliculi
For sensory orientation of the body; head, eye, trunk movements

28
Q

Rubrospinal pathway

A

Dorsolateral
Crossed
From red nucleus in midbrain
Involved in limb movement

29
Q

Corticospinal pathway/pyramidal

A

Dorsolateral
From cortex via brainstem to spinal cord
Goal directed movement esp upper limbs used for manipulation

30
Q

Vestibular reflex: postural instability

A

Head movement generates vestibular signal which acts via feedforward pathway to generate extensor contraction to hold body up

-> Predictive feedforward command learnt using cerebellum

31
Q

Vestibular reflex: neck reflexes

A

Neck proprioceptors used to work out if we are falling or if neck just being bent

They generate equal and opposite signals to vestibular reflex so there is no loss of equilibrium

Cerebellum learns this; uses efferent copy to predict expected head movements (when bending neck) to work out what vestibular signals will be

32
Q

Vestibulocolic reflex

A

In small animals and babies

Compensatory neck contraction when body moves to keep head stable and fix gaze

33
Q

Vestibuloocular reflex

A

Equal and opposite movement of the eyes to the head movement to keep eyes fixed relative to image

34
Q

Optokinetic system

A

Drift and saccade sequence (nystagmus) to fix image on retina (gaze fixing) when following slow movement
Fast movement of eye because harder to get detail when moving it

35
Q

Gaze shifting

A

Moving eyes to seek out different images i.e to foveate on visual stimuli detected on retina
- Involves the superior colliculus (and its projections)

36
Q

Smooth pursuit

A

Feedforward mechanisms to move eyes with the (predicted) movement of an image to track it
Involving cortex and cerebellum

37
Q

Additional tract found in apes and humans

A

Cortico-motoneuronal pathway to bypass interneurons and project straight to spinal motoneurons

For finger movement

-> Development of these pathways starts at 9 months, same age dexterity starts to develop

38
Q

Problems with motor cortex homunculus

A

There is overlap between areas of cortex from which different body part movements can be evoked

Corticospinal axons terminate in multiple motor nuclei from different motoneuron pools; can activate synergistic muscles used in specific movements

39
Q

Lateral premotor cortex

A

Integrates visual and proprioceptive information into the movement pathway
- Lesions here cause inappropriate movement of the contralateral hand in space

Mirror neurons

40
Q

Supplementary motor area

A

For planning movements and mental rehearsal

- Get activity here both when doing a movement pattern and thinking about doing it

41
Q

Cingulate motor areas

A

For emotionally driven gestures like the limbic laugh

42
Q

Mirror neurons

A

Active both when performing a movement and when watching someone else do it
Suggested to be involved in learning by imitation and empathy

First discovered (and mainly found in) the premotor cortex

43
Q

Long latency reflexes

A

Cutaneous: tactile mechanoreceptors can detect slips between object and fingertips and signal to motor cortex (via DCN and ventrolat thalamus) to activate muscles to reinforce grip (requires slowing down of the original action)

Stretch: as well as past stretch reflex, get projection via DCN and ventrolat thalamus to the motor cortex to cause smaller long latency reflex to reinforce the movement

44
Q

Dysmetria

A

Inappropriate displacement of movement i.e under or over reaching
(cerebellar damage)

45
Q

Dysdiadochokinesia

A

Inability to make rapid, alternating movements

cerebellar damage

46
Q

Signal carried by mossy fibre

A

From cortex and proprioceptors
Error signal (using sensory info and efferent copy)
Carries context; the conditional stimulus e.g sound in eyeblink conditioning

47
Q

Climbing fibre input

A

From the inferior olivary nucleus
Carries instructive signal; i.e unconditional stimulus like periocular eye puff

Helps establish what movement is the right one to strengthen for that context?

48
Q

Motor learning in cerebellum

A

Learned pattern of activity in mossy fibres will automatically generative the appropriate movement (by not inhibiting certain outputs)

Automating outputs to free it from conscious control

49
Q

Movement calibration in the vestibule-ocular reflex

A

Canals signal to the cerebellum (flocculus) and the vestibular nuclei

Vestibular nuclei activity is balance of excitation from canals and inhibition from cerebellum

50
Q

Adjusting vestibular-ocular reflex

A

Climbing fibres activated by retinal slip; carry error signal
Leads to adjustment of the feedforward model

51
Q

Chorea

A

Involuntary, unpredictable movements (BG damage)

52
Q

Ballismus

A

Unpredictable flailing movements (BG damage)

53
Q

Bradykinesia

A

Slowness of movement (BG damage)

54
Q

Hyperkinesia

A

Too much movement and at inappropriate times but still well coordinated

55
Q

Direct pathway in basal ganglia

A

Dopamine from substantial nigra acts on D1 receptors in striatum
This activates the direct pathway to inhibit GPint
This relieves the inhibition on the thalamus so motor plans can get through

56
Q

Indirect pathway in basal ganglia

A

Lack of dopamine from substantial nigra means it doesn’t inhibit indirect pathway via D2 receptors

So get inhibition of GPext
This relieves inhibition on sub thalamus so it is free to excite GPint
GPint can then inhibit the thalamus to stop motor plans getting through

57
Q

Hyperdirect pathway in basal ganglia

A

Motor cortex can direction excite sub thalamic nucleus to excite GPint, causing inhibition on thalamus for rapid braking of movement

58
Q

Treating Parkinson’s

A

Provide L-DOPA to replacement dopamine
Pallidotomy; controlled GPint lesions
Deep brain stimulation of sub thalamic nucleus to reduce excitation on GPint

59
Q

Dorsal striatum output function

A

Related to motor function

60
Q

Ventral striatum output function

A

To limbic function which motivates decisions about future movement
- Projects to prefrontal cortex and cingulate prefrontal cortex

61
Q

Role of BG in controlling visual saccades to foveate on stimuli

A

GP acts to tonically inhibit the superior/rostral colliculus that drives visual saccades

So must disinhibit this with striatum activity (need cortical input for this)

62
Q

Spiny neurons in the striatum

A

Get corticostriate input (excitatory); this is instructive signal for learning
Input from dopaminergic neurons of substance nigra to act as reinforcer
-> If an output from BG was successful, there will be a release of dopamine which reinforces the synapses used via LTP

Habit learning

63
Q

Fact that motor system ca achieve a goal in multiple ways

A

Motor equivalence problem

NAB (8 decks)

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