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1B motor control Flashcards

1
Q

What is hierarchical organisation?

A
  • High order areas of hierarchy are involved in more complex tasks (programme and decide on movements, coordinate muscle activity)
  • Lower level areas of hierarchy perform lower level tasks (execution of movement)
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2
Q

What is functional segregation?

A

Motor system is organised in a number of different areas that control different aspects of movement

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3
Q

Which tracts are pyramidal?

A
  • Corticospinal
  • Corticobulbar
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4
Q

Why are pyramidal tracts called pyramidal?

A

They pass through the pyramids of the medulla

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5
Q

Where do the nerves of the pyramidal tracts go from and to?

A

From motor cortex to spinal cord or cranial nerve nuclei in brainstem

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6
Q

What do the nerves of the pyramidal tracts control?

A

Voluntary movements of body and face

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7
Q

What tracts are extrapyramidal?

A
  • Vestibulospinal
  • Tectospinal
  • Reticulospinal
  • Rubrospinal
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8
Q

What does the vestibulospinal tract do?

A
  • stabilise head during body movements or as head moves
  • Coordinate head movements with eye movements
  • mediate postural adjustments
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9
Q

What does the tectospinal tract do and where is it from?

A
  • from superior colliculus of midbrain
  • orientation of head and neck during eye movements
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10
Q

What does the reticulospinal tract do and where is it from?

A
  • Most primitive descending tract- from medulla and pons
  • Changes in muscle tone associated with voluntary movements
  • postural stability
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11
Q

What does the rubrospinal tract do and where is it from?

A
  • From red nucleus of midbrain
  • In humans mainly taken over by corticospinal tract
  • Innervate lower motor neurones of flexors of upper limb
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12
Q

Why are they called extrapyramidal?

A

Don’t pass through the pyramids of the medulla

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13
Q

Where do the nerves of extrapyramidal tracts go from and to?

A
  • UMN in cortex
  • LMN in brainstem nuclei to spinal cord
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14
Q

What do the nerves of the extrapyramidal tract control?

A

Involuntary (automatic) movements for balance, posture and locomotion

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15
Q

What is the primary motor cortex responsible for?

A
  • Controls fine, discrete, precise voluntary movements
  • Provides descending signals to execute movements
  • It’s the final common pathway from the brain down to LMN in brainstem or spinal cord
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16
Q

What is the premotor cortex responsible for?

A
  • Located anterior to primary motor cortex
  • Involved in planning movements
  • Regulates externally cued movements e.g. seeing an apple and reaching out for it
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17
Q

What is the supplementary motor area responsible for?

A
  • Located anterior and medial to primary motor cortex
  • Involved in planning complex movements (e.g. internally cued, speech)
  • Becomes active prior to voluntary movement
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18
Q
A
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19
Q

What does the oculomotor nerve from the trochlear nuclei do?

A

Eye movements

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20
Q

What does the trigeminal motor nucleus do?

A

Muscles of the jaw

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21
Q

What does the abducens nucleus do?

A

Eye movement

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22
Q

What does the facial nucleus control?

A

Muscles of the face

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23
Q

What does the hypoglossal nucleus control?

A

The tongue

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24
Q

What are the negative signs of an upper motor neuron lesion?

A
  • Paresis- graded weakness of movements
  • Paralysis (plegia)- complete loss of voluntary muscle activity
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25
Q

What are the positive signs of an upper motor neuron lesion?

A
  • Increased abnormal motor function due to loss of inhibitory descending inputs
  • Spasticity- increased muscle tone
  • Hyper-reflexia- exaggerated reflexes
  • Clonus- abnormal oscillatory muscle contraction
  • Babinski’s sign
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26
Q

What is apraxia?

A
  • A disorder of skilled movement- patients aren’t paretic but have lost info about how to perform skilled movements
  • Due to a lesion of inferior parietal lobe or frontal lobe (premotor cortex, supplementary motor area)
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27
Q

What are the 2 most common causes of apraxia?

A

Stroke and dementia

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28
Q

Describe this image

A

MRI of patient with bilateral SMA (supplementary motor area) infarct

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29
Q

What does a lower motor neuron lesion cause?

A
  • Weakness
  • Muscle atrophy
  • Hypotonia (reduced muscle tone)
  • Hyporeflexia (reduced reflexes)
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30
Q

What are fasciculations?

A

Damaged motor units produce spontaneous action potentials, resulting in a visible twitch

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31
Q

What are fibrillations?

A

Spontaneous twitching of individual muscle fibres- recorded during needle electromyography examination

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32
Q

What is Motor Neurone Disease?

A

Progressive neurodegenerative disorder of the motor system

It’s a spectrum of disorders

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33
Q

What is MND also known as in the US?

A

Amyotrophic lateral sclerosis (ALS)

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34
Q

What are the UMN signs for MND?

A
  • Spasticity
  • Brisk limbs and jaw reflexes
  • Babinski’s sign
  • Loss of dexterity
  • Dysarthria (difficulty speaking)
  • Dysphagia (difficulty swallowing)
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35
Q

What are the LMN signs for MND?

A
  • Weakness
  • Muscle wasting
  • Tongue fasciculations and wasting
  • Nasal speech
  • Dysphagia
36
Q

What are the parts to the basal ganglia?

A
  • Caudate nucleus
  • Lentiform nucleus (putamen + external global pallidus)- putamen & caudate together are known as striatum
  • Nucleus accumbens
  • Subthalamic nuclei
  • Substantia nigra (midbrain)
  • Ventral pallidum, claustrum, nucleus basalis (of Meynert)
37
Q

What are the functions of the basal ganglia?

A
  • Decision to move
  • Elaborating associated movements (e.g. swinging arms when walking; changing facial expression to match emotions)
  • Moderating and coordinating movement (suppressing unwanted movements)
  • Performing movements in order
38
Q
A
  • C: caudate nucleus
  • P: putamen
  • G: external global pallidus
  • T: thalamus
  • Acc: nucleus accumbens
  • Am: amygdala
  • AC: anterior commisure
39
Q

Describe the basal ganglia circuitry

A
40
Q

What is Parkinson’s?

A

Degeneration of the dopaminergic neurones that originate in the substantia nigra and project to the striatum

41
Q

What are the symptoms of Bradykinesia?

A

Slowness of small movements (doing up buttons, handling a knife)

42
Q

What are the symptoms of Akinesia?

A

Difficulty in initiation of movements because can’t initiate movements internally

43
Q

What are the symptoms of Hypomimic face?

A

Expressionless, mask-like (absence of movements that normally animate the face)

44
Q

What are the symptoms of rigidity?

A

Muscle tone increase, causing resistance to externally imposed joint movements

45
Q

What is tremor at rest?

A

4-7 Hz, starts in one hand (pill-rolling tremor) and with time it spreads to other parts of the body

46
Q

What does this show?

A
47
Q

What is Huntington’s

A

Degeneration of inhibitory GABAergic neurones in the striatum → caudate and then putamen

48
Q

What is the aetiology of Huntington’s?

A

It’s genetic- autosomal dominant, chromosome 4 has a CAG repeat

49
Q

What are the symptoms of Huntington’s?

A
  • Choreic movements (chorea is dance)- rapid jerky involuntary movements of body
    • Hands and face affected first
    • Then legs
    • Then rest of body
  • Speech impairment
  • Dysphagia
  • Unsteady gait
  • Later stages has cognitive decline and dementia
50
Q

What is ballism?

A
  • usually from stroke affecting subthalamic nucleus
  • generally one sided and causes uncontrolled flinging of extremities
  • Symptoms occur contralaterally
51
Q

Describe the brain of normal vs Huntington’s disease

A
52
Q

Where is the cerebellum?

A
  • Located in posterior cranial fossa
  • Separated from cerebrum above by tentorium cerebelli
53
Q

What does the cerebellum do overall?

A

Coordinator and predictor of movement

54
Q

What does the vestibulocerebellum do?

A
  • Regulation of gait, posture and equilibrium
  • Coordination of head movements with eye movements
55
Q

What does a lesion in the vestibulocerebellum do?

A

Damage (tumour) causes syndrome similar to vestibular disease leading to gait ataxia (unsteady, staggering gait) and tendency to fall (even when patient sitting and eyes open)

56
Q

What does the spinocerebellum do?

A
  • Coordination of speech
  • Coordination of limb movements
  • Adjustment of muscle tone
57
Q

What does damage to the spinocerebellum do?

A

Damage (degeneration and atrophy associated with chronic alcoholism) affects mainly legs, causes abnormal gait and stance (wide-based)

58
Q

What does the cerebrocerebellum do?

A
  • Coordination of skilled movements
  • Cognitive function
  • Attention
  • Processing of language
  • Emotional control
59
Q

What does damage to the cerebrocerebellum section do?

A

Damage affects mainly arms/skilled coordinated movements (tremor) and speech

60
Q

What are the main signs of cerebellar dysfunction?

A

These are apparent only on movement

61
Q

What is ataxia?

A

General impairments in movement coordination and accuracy

Disturbances of posture or gait: wide-based, staggering ‘drunken’ gait

62
Q

What is dysmetria?

A

Inappropriate force and distance for target-directed movements (knocking over a cup rather than grabbing it)

63
Q

What is intention tremor?

A

Increasingly oscillatory trajectory of a limb in a target-directed movement (nose-finger tracking)

64
Q

What is dysdiadochokinesia?

A

Inability to perform rapidly alternating movements (rapidly pronating and supinating hands and forearms)

65
Q

What is scanning speech?

A

Staccato, due to impaired coordination of speech muscles

66
Q

What do alpha motor neurones do?

A

They are the lower motor neurones of the brainstem and spinal cord

They innervate the extrafusal muscle fibres of the skeletal muscle and their activation causes muscle contraction

67
Q

Where are alpha motor neurones located?

A

In the anterior horn of grey matter of spinal cord

also located in the brainstem

68
Q

What is the motor neuron pool?

A

Contains all alpha motor neurones innervating a single muscle

69
Q

Define a reflex

A

An automatic response to a stimulus that involves a nerve impulse passing inward from a receptor to a nerve centre and then outward to an effector without reaching the level of consciousness

the magnitude and timing of which are determined respectively by the intensity and onset of the stimulus

70
Q

How are reflexes different to voluntary movements?

A

Once reflexes are released, they can’t be stopped

71
Q

What are reflexes thought of as?

A

Automatic (knee jerk) and stereotyped behaviours (sneeze, cough) in response to stimulation of peripheral factors

72
Q

What is the Jendrassik manouevre?

A

If you clench your teeth, make a fist or pull against locked fingers when your patellar tendon is tapped, the reflex becomes larger

73
Q

Why does Jendrassik manouevre occur?

A

This removes the descending inhibition from the brain

74
Q

Describe the inhibitory control of the brain on reflexes + what is decerebation?

A
  • Higher centres of the CNS exert inhibitory and excitatory regulation upon the stretch reflex
  • Inhibitory control dominates in normal conditions (N on graph)
  • Decerebration reveals the excitatory control from supraspinal areas (D on graph)
75
Q

What can cause rigidity and spasticity based on decerebration?

A

Rigidity and spasticity can result from brain damage giving over-active or tonic stretch reflex

76
Q

Describe what’s happening here

A
  • Researchers took a cat and stretched a muscle
  • Under normal conditions, there was a reflex increase in force produced by the muscle
  • When the cat was decerebrated, the cerebral cortex was separated from lower spinal cord, the muscle was stretched again and there was a greater reflex response along with the muscle going into an elevated level tonic contraction
77
Q

What are the neuron activation pathways that produce descending spinal reflexes?

A

1) Activating alpha motor neurones
2) Activating inhibitory interneurons
3) Activating propriospinal neurones
4) Activating gamma motor neurones
5) Activating terminals of afferent fibres

78
Q

What do activating alpha motor neurones do?

A

Normal UMN → LMN → muscle to cause contraction

79
Q

What do activating propriospinal neurones do?

A

Interneurons that go up and down spinal cord a bit to activate nearby muscles

80
Q

What do activating gamma motor neurones do?

A

Innervate and alter sensitivity of sensory organs within intrafusal muscle fibres so it can remain sensitive to stretch when muscle is at different length

81
Q

What do activating terminals of afferent fibres do?

A

Fibres that have synaptic connections with sensory and motor terminals

82
Q

What is hyperreflexia?

A
  • Overactive reflexes
  • Loss of descending inhibition
  • Associated with UMN lesion
83
Q

What is clonus?

A
  • A sign of UMN dysfunction
  • Involuntary and rhythmic muscle contractions
  • Loss of descending inhibition
84
Q

What is Babinski’s sign?

A

When sole stimulated with blunt instrument, the big toe:

  • Curls downwards- normal response
  • Curls upwards- abnormal in adults and is a positive Babinski sign
  • Associated with UMN lesions of corticospinal tract

‘Plantar extension response’

85
Q

What is important to know about infants when looking for Babinski’s sign?

A

Toe curls upwards in infants- this is normal

86
Q

What is hyporeflexia?

A
  • Below normal or absent reflexes
  • Associated with lower motor neurone diseases

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