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MedST IB: Neurobiology and Human Behaviour (NHB) > 8.0 Motor Systems > Flashcards

8.0 Motor Systems Flashcards

1
Q

What is a consequence of a lesion in:<br></br><br></br>a) Association cortex<br></br>b) Cerebellum<br></br>c) Brainstem<br></br>d) lower motor neuron<br></br>e) Primary motor cortex/upper motor neuron<br></br>f) Basal ganglia

A

a) Association cortex → apraxia<br></br>b) Cerebellum → Ataxia/poor coordination<br></br>c) Brainstem → Postural deficits<br></br>d) lower motor neuron → Flaccid paralysis<br></br>e) Primary motor cortex/upper motor neuron → Spastic paralysis <br></br>f) Basal ganglia → Hyper/hypokinesia

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2
Q

Upper motor neuron vs lower motor neuron lesions:

A

Upper motor neuron = exaggerated reflexes + spastic paralysis<br></br><br></br>Lower motor neuron = Loss of reflexes + flaccid paralysis

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3
Q

Define ataxia:

A

Neurological disorder of voluntary coordination of muscle movements

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4
Q

What is noise (with regards to neural signals)?

A

Random variation in neural signals

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5
Q

What is the motor equivalence problem?

A

Describes redundancy in the motor system<br></br>Goal directed movement can be achieved in different ways

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6
Q

Define non-linearity

A

Mixing individual motor commands does not produce predictable results

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7
Q

Define non-stationarity

A

Behaviour of motor systems can change over time<br></br><br></br>Muscle contraction depends on history (thixotropy)

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8
Q

Define thixotropy

A

Muscle contraction depends on history

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9
Q

Define negative feedback systems:

A

A sensed parameter is compared to a desired ‘set point’<br></br>If they match → no output<br></br>If they differ → system will generate a corrective action

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10
Q

Examples of negative feedback systems:

A

1) Blood glucose<br></br>2) Temperature<br></br>3) Respiration rate<br></br>4) Blood pressure

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11
Q

Advantages of negative feedback systems:

A

Automatically compensate for unpredicted events that cause deviation from set point (e.g. noise)

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12
Q

Disadvantages of negative feedback systems:

A

1) Time delays (error signal can be out of date by the time it reaches brain)<br></br>2) Instability and oscillation

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13
Q

Define feed-forward systems:

A

Motor commands are prepared (by estimation) in advance based on sensory information available<br></br><br></br>Fast movements need feed-forward predictive control

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14
Q

What is an internal model system?

A

Brain contains an internal model system - it is a representation of the mechanics of the body and the behaviour of the external world

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15
Q

What are the two types of the internal model system?

A

1) Inverse model<br></br>- Starts with desired movement<br></br>- Needs to be learnt<br></br><br></br>2) Forward model<br></br>- Predicts the consequences of motor commands (before and during movement)<br></br>- Needs internal feedback or efference copy

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16
Q

Define efference copy

A

An internal copy created of the efferent motor signal, which is input into a forward model

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17
Q

What brain structures are regarded as centres for feedforward control?

A

1) Cerebellum<br></br>2) Motor cortex

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18
Q

Where are the alpha-motoneurons located in the spinal cord?

A

Ventral horn

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19
Q

Define a motor unit:

A

All the muscle fibres innervated by 1 motoneuron

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20
Q

What are the different motor unit categories?<br></br><br></br>Comment on anatomy, biochemistry and physiology

A

“<div><img></img></div>”

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21
Q

What is rate coding?

A

Mechanism of controlling motoneurons<br></br><br></br>Varying the motorneuron firing rate

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22
Q

What is motorneuron recruitment?

A

Mechanism of controlling motoneurons (more important than rate coding)<br></br><br></br>Varying the number of motoneurons recruited (↑ force needed → ↑ motoneurons recruited)

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23
Q

Define the size principle (motoneuron recruitment):

A

Motor units are recruited to action in an orderly sequence of increasing force

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24
Q

What are the 3 sources of input into motoneurons?

A

1) Spinal interneurons (most numerous)<br></br>2) Afferent fibres (only from muscle spindles)<br></br>3) Descending fibres (rare)

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25
Q

What is a proprioceptor?

A

A receptor that provides information about the state of the body (position/movement of joints/muscle force etc)

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26
Q

Define proprioception:

A

Perception of position and movement of the body (a.k.a. kinaestheia)

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27
Q

3 types of proprioceptors in motor system:

A

1) Muscle spindles afferents (signal stretch)<br></br>2) Golgi tendon organ afferents (signal tension)<br></br>3) Joint receptors (signal position and movement)

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28
Q

What are the different types of fibre in a muscle spindle?

A

1) Intrafusal<br></br>2) Extrafusal

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29
Q

What are the two types of fibre in an intrafusual fibre?

A

1) Bag fibre (dynamic response to changes in muscle length)<br></br>2) Chain fibre (Static response. Linear response)

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30
Q

What are the two types of sensory fibres in each intrafusal fibre?

A

1) Primary (Ia) spindle afferent (Aα)<br></br>2) Secondary (II) spindle afferent (Aβ)

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31
Q

What are the motorneurons that supply the muscle spindles? What is their role?

A

γ-motorneurons<br></br><br></br>Play a role in sensitisation and adaptation of receptors

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32
Q

Draw a stretch reflex:

A

“<div><img></img></div>”

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33
Q

Define reciprocal inhibition:

A

Stimulation of one agonist pathway also excites spinal interneurons that inhibit antagonist muscles

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34
Q

Define muscle clonus:

A

Brief involuntary muscle contraction (often repeated and rhythmic)

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35
Q

Define recurrent inhibition:

A

Motorneurons have recurrent collateral branches that innervate an inhibitory interneuron (Renshaw cell) to provide recurrent inhibition of the motorneuron, thus regulating the timing of motor neuron firing.

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36
Q

What are some normal neonatal reflexes?

A

1) Grasp reflex<br></br>2) Babinski’s sign<br></br>3) Reflex stepping

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37
Q

Define spasticity:

A

Exaggerated stretch reflexes (muscles are tense and stiff)

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38
Q

Define Babinski’s sign:

A

Toes turn up to plantar stimulation (normal for neonates, pathological in adults [due to cortical damage])

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39
Q

Define clasp knife reflex:

A

Limbs snap into extension or flexion

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40
Q

Define central pattern generators:

A

Central pattern generators (CPGs) are biological neural networks that produce rhythmic patterned outputs without sensory feedback

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41
Q

Muscle spindles comprise a fibrous capsule that contains a number of ____________ muscle fibres. The large primary afferent arising from the muscle spindle arise from annulospiral terminals on these fibres and respond to __________, however taken alone the signals are ambiguous as they can be altered by _______________. The central connections of the muscle spindle afferents include monosynaptic connections with motorneurones of the agonist muscle and with interneurones that mediate _____________inhibition of antagonist motorneurons. In addition to roles in reflex action and in proprioception, a very important role for the signals from muscle spindles is ______________.

A

Muscle spindles comprise a fibrous capsule that contains a number of <b>intrafusal</b> muscle fibres. The large primary afferent arising from the muscle spindle arise from annulospiral terminals on these fibres and respond to <b>change in length</b>, however taken alone the signals are ambiguous as they can be altered by <b>contraction of the intrafusal fibres</b>. The central connections of the muscle spindle afferents include monosynaptic connections with motorneurones of the agonist muscle and with interneurones that mediate <b>reciprocal</b> inhibition of antagonist motorneurons. In addition to roles in reflex action and in proprioception, a very important role for the signals from muscle spindles is <b>predictive feedforward control</b>.

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42
Q

What are the different descending motor pathways?

A

<b>Ventromedial pathways</b><br></br>1) Reticulospinal<br></br>2) Vestibulospinal<br></br>3) Tectospinal<br></br><br></br><b>Dorsolateral pathways</b><br></br>1) Corticospinal<br></br>2) Rubrospinal

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43
Q

What are the different functions of ventromedial and dorsolateral pathways?

A

<b>Ventromedial pathways</b><br></br>Controls axial + proximal limb muscles<br></br>Invovled in whole body movements like locomotion and posture<br></br><br></br><b>Dorsolateral pathways</b><br></br>Goal directed movements of the limbs (hand and feet) and face

44
Q

List 3 systems that contribute to postural stability:

A

1) Visual system<br></br>2) Vestibular system<br></br>3) Somatosensory and proprioceptive systems

45
Q

What are the receptors in the vestibular system?

A

1) Sensory hair cells (in semi-circular canals of labyrinth)<br></br><br></br>2) Otolith organs (saccule and utricle)

46
Q

Define vestibular reflexes:

A

Vestibular signals generated from head movement to generate correcting responses (usually via vestibulospinal pathways acting on extensor muscles)

47
Q

Define neck reflexes:

A

Equal and opposite reflexes to vestibular reflexes, to discriminate between head tilting and body swaying

48
Q

Peripheral disease that can affect vestibular reflexes:

A

Labyrinthitis

49
Q

Define gaze fixing:

A

Mechanisms used to keep eyes fixed relative to outside world<br></br><br></br>1) Vestibulo-ocular reflex<br></br>2) Optokinetic reflex

50
Q

Define Vestibulo-ocular reflex:

A

A gaze-fixing mechanism where vestibular system detects head movement and drives compensatory (equal and opposite) eye movements

51
Q

Define Optokinetic reflex:

A

A gaze-fixing mechanism where eyes move to follow the slow movement of the visual field

52
Q

Define Nystagmus:

A

Sawtooth movement of eye caused by drift and saccade sequence

53
Q

Causes of nystamus:

A

<b>Physiological</b><br></br>- Response to optokinetic or vestibular stimuli<br></br><br></br><b>Pathological</b><br></br>- Cerebellar damage<br></br>- Vestibular damage

54
Q

Define gaze shifting:

A

Mechanisms used to move the eyes as quickly as possible to minimise the blurring period that occurs when eyes are moving

55
Q

Define saccade:

A

Gaze shifting mechanism that quickly moves the eye to foveate visual stimuli

56
Q

Neuronal structures involved in saccade production:

A

1) Retina<br></br>2) Superior colliculus<br></br>3) Brainstem reticular formation<br></br>4) Cervical spinal cord<br></br>5) Basal ganglia<br></br>6) Oculomotor nuclei

57
Q

Define smooth pursuit:

A

Gaze-shifting mechanism where slower eye movements are used to ‘follow’ moving objects.<br></br><br></br>Feedforward predictive movement

58
Q

Neuronal structures involved in smooth pursuit:

A

Cerebral cortex<br></br>Cerebellum

59
Q

Location of motor cortex?

A

Frontal lobe (immediately rostral to central sulcus)

60
Q

Role of motor association areas?

A

Involved with planning and preparation for action

61
Q

Define hemiparesis:

A

Weakness/partial paralysis to one side of the body

62
Q

Define hemiplegia:

A

Paralysis to one side of the body

63
Q

What is unique to the corticospinal tracts in primates?

A

Corticomotoneuronal connections (some of the fibres in the corticospinal tract make direct conenctions with α-motorneurons)

64
Q

What does an upper motor neuron cause?

A

Spastic paralysis

65
Q

Signs of spastic paralysis?

A

1) Hypertonia<br></br>2) Hyperreflexia<br></br>3) Clonus

66
Q

What does an lower motor neuron cause?

A

Flaccid paralysis

67
Q

Signs of flaccid paralysis?

A

1) Hypotonia<br></br>2) Loss of reflexes

68
Q

What goal directed movement does not occur via the motor cortex (corticospinal tract)?

A

Eye movements - because these need to be consensual to avoid diplopia<br></br><br></br>They have separate area of cortex which control movement via the brain stem

69
Q

Why is the motor homunculus misleading?

A

Suggests an orderly representation of individual muscles in different regions of the cortex. This is not the case as a lesion in one location does not only affect one specific muscle/body part. It is more likely that muscles are represented in synergistic muscle groups.

70
Q

Give an example of a movement that is controlled by feedback control:

A

Finger grip force

71
Q

Give an example of a movement that cannot be controlled by feedback control:

A

Eye movement

72
Q

Define long latency stretch reflex:

A

As well as spinal reflex, there is also a stretch reflex involving the cortex. This is slower but allows the brain to set its gain

73
Q

What are the regions of motor association areas?

A

<b>1) Lateral premotor cortex</b><br></br>- Connected with sensory areas and cerebellum<br></br>- Important for sensory guided movement (esp. vision guided movements)<br></br><br></br><b>2) Supplementary motor area (SMA)</b><br></br>- Connected to many cortical areas + basal ganglia<br></br>- Important for internally generated movements<br></br><br></br><b>3) Cingulate motor area</b><br></br>- Expression of emotion via motor system

74
Q

What are the connections to the motor association areas?

A

<b>1) Primary motor area</b><br></br>- Direct<br></br>- To control current command for movement<br></br><b>2) Spinal cord</b><br></br>- Direct<br></br><b>3) Cerebellum + basal ganglia</b><br></br>- Indirect<br></br>- To plan and prepare for future movements

75
Q

What are mirror neurons?

A

Neurons in lateral premotor cortex<br></br>Neurons that fire in relation to making a movement but also in relation to seeing other make the movement (imitation)

76
Q

What evidence is available to show that supplementary motor area is used in internally generated movements?

A

PET scanning shows that this area is active in mental rehearsal

77
Q

Role of cerebellum:

A

Major role in feedforward control and Coordination of movement<br></br><br></br>Also learning

78
Q

What do cerebellar lesions cause?

A

<b>D</b>ysdiadochokinesis/Dysmetria<br></br><b>A</b>taxia<br></br><b>N</b>ystagmus<br></br><b>I</b>ntention tremor<br></br><b>S</b>lurred speech<br></br><b>H</b>ypotonia

79
Q

Define hypotonia:

A

State of low muscle tone with reduced muscle strength

80
Q

Define dysmetria:

A

Inappropriate displacement (e.g. overreaching)

81
Q

Define dysdiadochokinesis::

A

Inability to make rapid alternating movements

82
Q

Define decomposition of movement:

A

Lack of coordination of different joint movements

83
Q

Define dyskinesia:

A

Abnormality or impairment of voluntary movement. Unpredicted movements

84
Q

What are the output cells of the cerebellum?

A

Purkinje cells<br></br>- Tree-like in sagittal plane<br></br>- Narrow in coronal plane<br></br>- Project to and inhibit the cerebellar nuclei

85
Q

What neurotransmitter do Purkinje cells release?

A

GABA<br></br><br></br>They are inhibitory

86
Q

How many layers are there in the cerebellar cortex?

A

3<br></br><b>1) Molecular layer</b><br></br>- Granule cell axons<br></br>- Dendrites of Purkinje cells<br></br><b>2) Purkinje cell layer</b><br></br>- Single cell thick<br></br><b>3) Granule layer</b><br></br>- Vast number of small granule cells

87
Q

Function of granule cells in cerebellum:

A

“Give rise to parallel fibres that EXCITE purkinje cells<br></br><br></br>1 Purkinje can ““listen”” to 200,000 granule cells”

88
Q

What are the two inputs to the cerebellum?

A

<b>1) Mossy fibres</b><br></br>- Most numerous<br></br>- From pons<br></br>- Excite granule cells<br></br><br></br><b>2) Climbing fibres</b><br></br>- From inferior olive<br></br>- Each Purkinje fibre receives single climbing fibre<br></br>- Mediate learning (synaptic plasticity)

89
Q

What region in the cerebellum is responsible for the vestibulo-ocular reflex?

A

Flocculus

90
Q

What is an inhibitory interneuron of the cerebellum?

A

Stellate cell

91
Q

What are the main nuclei of the basal ganglia?

A

Caudate<br></br>Putamen<br></br>Globus pallidus

92
Q

What are the two mid-brain nuclei that are functionally connected to the basal ganglia?

A

Subthalamic nuclei<br></br>Substantia nigra

93
Q

What are the inputs to the basal ganglia?

A

From all lobes of cerebral cortex

94
Q

What are the outputs of basal ganglia?

A

Inhibitory output to thalamus (GABA connections)

95
Q

Examples of hyperkinetic movements:

A

1) Chorea (unexpected dancing movements)<br></br>2) Athetosis (writhing movements of hands/face)<br></br>3) Ballismus (ballistic movements)<br></br>4) Dyskinesia

96
Q

Define Chorea:

A

Unexpected dancing movement

97
Q

Define athetosis:

A

Writhing movements of the hands/face

98
Q

Define ballismus:

A

Ballistic movements

99
Q

Examples of hypokinesia:

A

1) Rigidity<br></br>2) Bradykinesia

100
Q

Pyramidal vs Extra-pyramidal lesions:

A

Pyramidal = lesions of motor cortex/Corticospinal tract (eg caused by stroke)<br></br><br></br>Extra-pyramidal = Lesions of basal ganglia

101
Q

Which part of the globus pallidus does direct pathway go to?

A

Internal globus pallidus

102
Q

Which part of the globus pallidus does indirect pathway go to?

A

External globus pallidus

103
Q

Effect of dopamine on direct and indirect pathways of basal ganglia:

A

Stimulates direct (D1 receptor)<br></br>Inhibits indirect (D2 receptor)

104
Q

What is the role of the basal ganglia:

A

Decision making

105
Q

What is the role of the ventral striatum?

A

Part of the limbic system. Plays a role in emotion and motivation

MedST IB: Neurobiology and Human Behaviour (NHB) (11 decks)

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