Flashcards in 8.0 Motor Systems Deck (105)
What is a consequence of a lesion in:
a) Association cortex
d) lower motor neuron
e) Primary motor cortex/upper motor neuron
f) Basal ganglia
a) Association cortex → apraxia
b) Cerebellum → Ataxia/poor coordination
c) Brainstem → Postural deficits
d) lower motor neuron → Flaccid paralysis
e) Primary motor cortex/upper motor neuron → Spastic paralysis
f) Basal ganglia → Hyper/hypokinesia
Upper motor neuron vs lower motor neuron lesions:
Upper motor neuron = exaggerated reflexes + spastic paralysis
Lower motor neuron = Loss of reflexes + flaccid paralysis
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
Goal directed movement can be achieved in different ways
Mixing individual motor commands does not produce predictable results
Behaviour of motor systems can change over time
Muscle contraction depends on history (thixotropy)
Muscle contraction depends on history
Define negative feedback systems:
A sensed parameter is compared to a desired 'set point'
If they match → no output
If they differ → system will generate a corrective action
Examples of negative feedback systems:
1) Blood glucose
3) Respiration rate
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1) Time delays (error signal can be out of date by the time it reaches brain)
2) Instability and oscillation
Define feed-forward systems:
Motor commands are prepared (by estimation) in advance based on sensory information available
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
- Starts with desired movement
- Needs to be learnt
2) Forward model
- Predicts the consequences of motor commands (before and during movement)
- 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?
2) Motor cortex
Where are the alpha-motoneurons located in the spinal cord?
Define a motor unit:
All the muscle fibres innervated by 1 motoneuron
What are the different motor unit categories?
Comment on anatomy, biochemistry and physiology
What is rate coding?
Mechanism of controlling motoneurons
Varying the motorneuron firing rate
What is motorneuron recruitment?
Mechanism of controlling motoneurons (more important than rate coding)
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)
2) Afferent fibres (only from muscle spindles)
3) Descending fibres (rare)
What is a proprioceptor?
A receptor that provides information about the state of the body (position/movement of joints/muscle force etc)
Perception of position and movement of the body (a.k.a. kinaestheia)
3 types of proprioceptors in motor system:
1) Muscle spindles afferents (signal stretch)
2) Golgi tendon organ afferents (signal tension)
3) Joint receptors (signal position and movement)
What are the different types of fibre in a muscle spindle?
What are the two types of fibre in an intrafusual fibre?
1) Bag fibre (dynamic response to changes in muscle length)
2) Chain fibre (Static response. Linear response)