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Neurophysiology & Human Behaviour > Motor systems > Flashcards

Motor systems Flashcards

1
Q

What are the functions of the motor system?

A
  1. To move in and manipulate elements of the external environment
  2. To maintain internal and external equilibrium (homeostasis, balance)
  3. Autonomic functions (e.g. respiration, gut motility…)
  4. Communication (speech, hand gestures, facial expression, writing…)
  5. Sensation
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2
Q

What are the types of basic movements?

A
  1. Reflex (e.g. knee-jerk, coughing…): Pre-programmed, simple movements that usually don’t require any CNS input and are automated. They are also rigid, stereotyped and occur in the same way each time in response to the same stimuli. They are usually a graded function of eliciting stimulus.
  2. Rhythmic (e.g. walking, chewing…): On-going motor actions in a set pattern repeated in set intervals. They are stereotyped and consist of a mixture of voluntary and reflex movements, but can be influenced by voluntary control.
  3. Voluntary (e.g. playing piano, catching ball…): Complex movements determined by particular external stimuli or internal motivation. They are usually goal driven and can be modified voluntarily to suit particular circumstances.
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3
Q

What factors make the motor system difficult to study?

A
  1. The motor system is non-linear as a result of convergence/divergence. This means no simple assumption can me made about its function (i.e. one cannot simply presume that if A occurs, B must also occur).
  2. Joints have many degrees of freedom, giving an endless combination of possible movements that are impossible to predict.
  3. Motor systems usually comprise a large networks containing thousands of neurones with thousands of integrating synapses. Understanding these networks require large amounts of information.
  4. Repetitive stimulation of a muscle causes gradual change in muscle response despite motor input remaining constant (thixotropy). This implies that motor output is also dependent on changes intrinsic to the muscles and effectors themselves.
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4
Q

What are the 2 rules concerned with organisation of motor neurones in the spinal cord?

A
  1. Proximal-distal rule: Motor neurones innervating proximal muscles (trunk, shoulder, hip) are more medial compared to those innervating distal muscles (fingers, toes…).
  2. Flexor-extensor rule: Motor neurones responsible for extension are more ventral compared to those responsible for flexion.
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5
Q

What are the types of motor units present in muscles?

A
  1. Slow motor units
  2. Fast motor units
  3. Fast (fatigue-resistant) motor units
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6
Q

What are the characteristics of slow motor units?

A
  • Few small fibres per unit.
  • Highly vascularised.
  • Generates small amount of tension.
  • Contraction can be sustained.
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7
Q

What are the characterstics of fast motor units?

A
  • Many large fibres per unit.
  • Low vascularisation.
  • Generates large amount of tension.
  • Contraction is only transient as fibres fatigue.
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8
Q

What are the characteristics of fast (fatigue-resistant) motor units?

A
  • Generates intermediate amount of tension.
  • Contraction can be sustained for longer than fast motor fibres.
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9
Q

What are the types of intrafusal fibres present in muscle spindles?

A
  1. Nuclear bag fibres
  2. Nuclear chain fibres
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10
Q

What are the afferent innervations of the various intrafusal fibres?

A
  • Nuclear bag: Ia (dynamic) + II (static)
  • Nuclear chain: II
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11
Q

What are the properties and functions of Ia afferents that innervate spindle fibres?

A
  • Adapting
  • Detection of muscle rate of change
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12
Q

What are the properties and functions of II afferents that innervate spindle fibres?

A
  • Non-adapting
  • Measures muscle length
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13
Q

What are the efferent γ fibres that innervate the muscle spindle fibres?

A
  • γS: Innervates nuclear chain fibres and increases sensitivity of II fibres
  • γD: Innervates nuclear bag fibres and increases sensitivity of Ia and II fibres
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14
Q

What are the contents of typical muscle spindle?

A
  • 1 Nuclear bag fibres (static)
  • 1 Nuclear bag fibre (dynamic)
  • Several nuclear chain fibres
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15
Q

What are the functions of muscle spindles?

A
  • Detects absolute muscle length or rate of change in muscle length
  • In parallel with muscle fibres
  • Used in feedback control of muscle length through “Servo hypothesis”
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16
Q

What are the functions of Golgi tendon organs?

A
  • Detects muscle tension
  • In series with muscle fibres
  • Causes negative feedback inhibition of associated muscles and stimulation of activity of antagonists to prevent damage by excess contraction
  • Causes positive feedback stimulation of associated muscles to provide powerful movements
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17
Q

What is the afferent innervation of Golgi tendon organs?

A

Ib fibres

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18
Q

What are the types of descending inputs into the spinal cord?

A
  1. Fast pathway: Uses NTs to exert fast control on transient and specific aspects of motor activity.
  2. Slow pathway: Uses neuromodulators to alter the long-term activity of spinal cord motor centres.
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19
Q

What are the components of the fast descending motor pathways?

A
  • Ventromedial pathways (controls movement of the proximal muscles of the trunk):
    1. Reticulospinal tract: Orientation and CPG activaton.
    2. Vestibulospinal tract: Postural control.
    3. Tectospinal tract: Orientation to sounds and objects.
    4. Corticospinal tract
  • Dorsolateral pathways (controls movement of distal muscles of the extremities):
    1. Rubospinal tract
    2. Corticospinal tract
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20
Q

What are the parts of the corticospinal tract?

A
  1. Decussating (~80%): Descends in the lateral corticospinal tract.
  2. Non-decussating (~20%): Descends in the ventral corticospinal tract.
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21
Q

How do vestibular nuclei distinguish between vestibular stimulation due to intended movement compared to loss of balance?

A
  • Internal models are able to predict vestibular changes due to intended movement.
  • When movement occurs, efferent copy sent back to CNS where vestibular response is predicted.
  • The predicted vestibular response is subtracted from actual response, any discrepancies are corrected for.
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22
Q

Which part of the reticular formation seems to be involved in mediating repetitive patterns?

A

Mesencephalic locomotor region

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23
Q

What is the location of the primary motor cortex (M1)?

A
  • Pre-central gyrus
  • Brodmann’s area 4
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24
Q

Where does M1 receive inputs from?

A
  1. Periphery and spinal cord
  2. Primary somatosensory cortex
  3. Sensory association areas
  4. Cerebellum
  5. Basal ganglia
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25
Q

What are the areas of the thalamus associated with the motor cortex?

A
  1. Ventrolateral nucleus: Projects into M1
  2. Ventroanterior nucleus: Projects into secondary motor areas
  3. Centromedial nuclei: Projects into both M1 and secondary motor areas
26
Q

Why does sensory information need to project into the cortex to be integrated with motor responses and not at spinal cord level?

A
  1. Spinal cord reflexes are very much restricted segmentally, in the sense that sensory information useful for particular motor activity may not synapse in dorsal horn of same spinal segment. M1 brings all sensory and motor endings into proximity, allowing appropriate signals to ‘jump’ across as necessary.
  2. The spinal cord is not intelligent enough to determine what appropriate motor responses are needed for given sensory input, and which motor fibres should be selectively activated, especially for movements that involve multiple muscle groups. Motor learning mediates this, but requires synaptic plasticity, which M1 offers.
27
Q

In what ways do somatosensation depend on motor activity?

A
  1. It is well established that many cutaneous mechanoreceptors (e.g. Pacinian corpuscules) are fully adapting, so constant movement is needed to sustain sensory input. This explains why the texture of a surface can only be successfully determined by moving across it, as opposed to placing hand in stationary on it.
  2. In order to accurately judge the sensation of an object, knowledge of amount of force being applied to object needs to be known.
28
Q

What is the organiation of M1 and its functional significance?

A
  • Fractured somatotopic arrangement
  • Allows for functional representations (i.e. one area of cortex controls all muscles involved in particular movements instead of in area of body)
29
Q

What locations does the cerebellum output to?

A
  1. Motor cortex
  2. Premotor areas
  3. Reticulospinal tract
  4. Rubrospinal tract
  5. Vestibulospinal tract
30
Q

What types of inputs are received by the cerebellum and where do they originate?

A
  1. Climbing fibres: Inferior olive
  2. Mossy fibres: Various peripheral and central sources
31
Q

What type of synapse is the climbing fibre-Purkinje cell synapse?

A

Aspartate (strong excitatory)

32
Q

What type of synapse is the granule cell-Purkinje cell synapse?

A

Glutamate (excitatory)

33
Q

What are the sources of the information carried by the climbing fibres?

A

Cerebral cortex (mainly)

34
Q

What are the sources of the information carried by the mossy fibres?

A
  1. Vestibular system
  2. Muscle proprioceptors
  3. Special senses
  4. Reticular fromation
  5. Cerebral cortex (via pons)
35
Q

Which sides of the body do each cerebellar hemisphere control?

A

Ipsilateral

36
Q

What are the different parts of the cerebellum and their associated functions?

A
  1. Vestibulocerebellum: Balance and posture
  2. Spinocerebellum: Internal feedback regulation of movements (using internal models)
  3. Cerebrocerebellum: Planning and initiation of voluntary movements
37
Q

What are the inputs and outputs of the vestibulocerebellum?

A

Vestibular nuclei

↓

Vestibulocerebellum

↓

Vestibular nuclei

38
Q

What are the inputs and outputs of the spinocerebellum?

A

Peripheral sensory infromation

↓

Spinocerebellum

↓

  1. Reticulospinal tract
  2. Vestibulospinal tract
39
Q

What are the inputs and outputs of the cerebrocerebellum?

A
  1. Sensory cortex
  2. Motor and premotor cortices
  3. Posterior parietal cortex

↓

Cerebrocerebellum

↓

  1. Premotor cortex
  2. Motor cortex
40
Q

What are the smaller lobules of the cerebellum called?

A

Folia

41
Q

What are the types of cells in the cerebellum?

A

Molecular layer:

  1. Basket cells
  2. Stellate cells

Purkinje layer: Purkinje cells

Granular layer:

  1. Granule cells
  2. Golgi cells
42
Q

What is the rule regarding nature of inputs into the cerebellum?

A
  • Climbing, mossy fibres are excitatory glutaminergic
  • Granule cells are excitatory glutaminergic
  • All other cells are inhibitory
43
Q

What types of action potentials are caused in Purkinje cells by the different input fibres to cerebellum?

A
  • Climbing fibres = Complex spike
  • Mossy fibres = Simple spike
44
Q

What are the types of circuits in the cerebellum?

A
  1. Direct circuits: Excitatory inputs of climbing and mossy fibres into deep nuclei.
  2. indirect circuits: Inhibitory inputs of Purkinje fibres to the deep nuclei.
45
Q

What evidence is there to suggest that motor learning is mediated by the cerebellum?

A
  1. Cerebellar activity changes during motor learning
  2. Motor learning is abolished following lesion of the cerebellum
  3. Lesion of the motor cortex abolishes subsequent motor learning but allows pre-learned actions to still be performed
46
Q

What are the effects of simultaneous climbing fibre and paralel fibre input into Purkinje cell?

A

Long term depression

47
Q

What are the symptoms of cerebellar lesion?

A
  1. Dysmetria: Over-reaching, resulting in intention tremors
  2. Hypotonia: Loss of muscle tone
  3. Dysdiadochokinesis: Inability to make rapid, repetitive movements
  4. Decomposition of movement: Complex movements are carried out in simple steps
  5. Scanning speech: Speech difficulties due to lack of coordination of lips and tongue
48
Q

What are the components of the basal ganglia?

A
  1. Putamen
  2. Caudate nucleus
  3. Globus pallidus
  4. Subthalamic nucleus
  5. Substantia nigra
49
Q

What are the components of the striatum?

A
  • Putamen
  • Caudate nucleus
50
Q

What are the sources of inputs into the basal ganglia?

A
  1. Motor cortex
  2. Sensory cortices
  3. Association cortices (main)
  4. Limbic system
51
Q

Which areas of the thalamus does the basal ganglia output into?

A
  • Ventroanterior
  • Ventrolateral
52
Q

What is the structure of the direct pathway in basal ganglia?

A
53
Q

What is the structure of the indirect pathway in basal ganglia?

A
54
Q

Why is the indirect basal ganglia pathway ‘indirect’?

A

It feeds into and modulates activity of the direct pathway.

55
Q

What are the effects of dopamine on individual areas of the basal ganglia?

A
  1. Promotes activity of striatum via D1 receptors
  2. Inhibits activity of globus pallidus (external segment) via D2 receptors
56
Q

What are the overall effects of dopamine on the basal ganglia?

A

Supports the direct pathway and inhibits indirect pathway,

57
Q

What are the symptoms of Parkinson’s disease?

A

“Classic triad”:

  1. Resting tremor (trembling of limbs only present in absence of movement
  2. Muscle stiffness
  3. Bradykinesia (slowness of movement and ‘shuffling gait’)
58
Q

What is Parkinson’s disease thought to be caused by?

A

Deficiency in dopamine from substantia nigra pars compacta

59
Q

What is the mechanism of pathogenesis for Parkinson’s disease?

A
  • Dopamine has the effect of promoting motor activity by promoting the direct pathway in basal ganglia and inhibiting indirect pathway.
  • Reduction in dopamine removes this motor activity-promoting effect and causes inhibition to dominate, resulting in hypokinesia in Parkinson’s.
60
Q

What are the treatments available for Parkinson’s disease?

A
  1. L-DOPA
  2. Foetal grafts
  3. Lesions
  4. Deep brain stimulation (DBS) of subthalamic nucleus
61
Q

What is Huntington’s disease thought to be caused by?

A

Degeneration of striatal GABAinergic neurones

62
Q

What is the mechanism of pathogenesis for Huntington’s disease?

A
  • Decreased output from striatum decreases disinhibition of globus pallidus external segment.
  • This in turn inhibits indirect pathway and promotes thalamus and increases motor activity, causing hyperkinesia.

Neurophysiology & Human Behaviour (20 decks)

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