8.0 Motor Systems Flashcards
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) 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
Upper motor neuron vs lower motor neuron lesions:
Upper motor neuron = exaggerated reflexes + spastic paralysis<br></br><br></br>Lower motor neuron = Loss of reflexes + flaccid paralysis
Define ataxia:
Neurological disorder of voluntary coordination of muscle movements
What is noise (with regards to neural signals)?
Random variation in neural signals
What is the motor equivalence problem?
Describes redundancy in the motor system<br></br>Goal directed movement can be achieved in different ways
Define non-linearity
Mixing individual motor commands does not produce predictable results
Define non-stationarity
Behaviour of motor systems can change over time<br></br><br></br>Muscle contraction depends on history (thixotropy)
Define thixotropy
Muscle contraction depends on history
Define negative feedback systems:
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
Examples of negative feedback systems:
1) Blood glucose<br></br>2) Temperature<br></br>3) Respiration rate<br></br>4) Blood pressure
Advantages of negative feedback systems:
Automatically compensate for unpredicted events that cause deviation from set point (e.g. noise)
Disadvantages of negative feedback systems:
1) Time delays (error signal can be out of date by the time it reaches brain)<br></br>2) Instability and oscillation
Define feed-forward systems:
Motor commands are prepared (by estimation) in advance based on sensory information available<br></br><br></br>Fast movements need feed-forward predictive control
What is an internal model system?
Brain contains an internal model system - it is a representation of the mechanics of the body and the behaviour of the external world
What are the two types of the internal model system?
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
Define efference copy
An internal copy created of the efferent motor signal, which is input into a forward model
What brain structures are regarded as centres for feedforward control?
1) Cerebellum<br></br>2) Motor cortex
Where are the alpha-motoneurons located in the spinal cord?
Ventral horn
Define a motor unit:
All the muscle fibres innervated by 1 motoneuron
What are the different motor unit categories?<br></br><br></br>Comment on anatomy, biochemistry and physiology
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What is rate coding?
Mechanism of controlling motoneurons<br></br><br></br>Varying the motorneuron firing rate
What is motorneuron recruitment?
Mechanism of controlling motoneurons (more important than rate coding)<br></br><br></br>Varying the number of motoneurons recruited (↑ force needed → ↑ motoneurons recruited)
Define the size principle (motoneuron recruitment):
Motor units are recruited to action in an orderly sequence of increasing force
What are the 3 sources of input into motoneurons?
1) Spinal interneurons (most numerous)<br></br>2) Afferent fibres (only from muscle spindles)<br></br>3) Descending fibres (rare)
2) Golgi tendon organ afferents (signal tension)
3) Joint receptors (signal position and movement)
2) Extrafusal
2) Chain fibre (Static response. Linear response)
2) Secondary (II) spindle afferent (Aβ)
Play a role in sensitisation and adaptation of receptors
2) Babinski's sign
3) Reflex stepping
1) Reticulospinal
2) Vestibulospinal
3) Tectospinal
Dorsolateral pathways
1) Corticospinal
2) Rubrospinal
Controls axial + proximal limb muscles
Invovled in whole body movements like locomotion and posture
Dorsolateral pathways
Goal directed movements of the limbs (hand and feet) and face
2) Vestibular system
3) Somatosensory and proprioceptive systems
2) Otolith organs (saccule and utricle)
1) Vestibulo-ocular reflex
2) Optokinetic reflex
- Response to optokinetic or vestibular stimuli
Pathological
- Cerebellar damage
- Vestibular damage
2) Superior colliculus
3) Brainstem reticular formation
4) Cervical spinal cord
5) Basal ganglia
6) Oculomotor nuclei
Feedforward predictive movement
Cerebellum
2) Hyperreflexia
3) Clonus
2) Loss of reflexes
They have separate area of cortex which control movement via the brain stem
- Connected with sensory areas and cerebellum
- Important for sensory guided movement (esp. vision guided movements)
2) Supplementary motor area (SMA)
- Connected to many cortical areas + basal ganglia
- Important for internally generated movements
3) Cingulate motor area
- Expression of emotion via motor system
- Direct
- To control current command for movement
2) Spinal cord
- Direct
3) Cerebellum + basal ganglia
- Indirect
- To plan and prepare for future movements
Neurons that fire in relation to making a movement but also in relation to seeing other make the movement (imitation)
Also learning
Ataxia
Nystagmus
Intention tremor
Slurred speech
Hypotonia
- Tree-like in sagittal plane
- Narrow in coronal plane
- Project to and inhibit the cerebellar nuclei
They are inhibitory
1) Molecular layer
- Granule cell axons
- Dendrites of Purkinje cells
2) Purkinje cell layer
- Single cell thick
3) Granule layer
- Vast number of small granule cells
1 Purkinje can ""listen"" to 200,000 granule cells"
- Most numerous
- From pons
- Excite granule cells
2) Climbing fibres
- From inferior olive
- Each Purkinje fibre receives single climbing fibre
- Mediate learning (synaptic plasticity)
Putamen
Globus pallidus
Substantia nigra
2) Athetosis (writhing movements of hands/face)
3) Ballismus (ballistic movements)
4) Dyskinesia
2) Bradykinesia
Extra-pyramidal = Lesions of basal ganglia
Inhibits indirect (D2 receptor)