Movement Flashcards
What are the five purposes of muscle contractions?
- Moving the external world
- Moving yourself around
- Maintaining equilibrium to prevent movements
- Communication
- Active touch
What is ‘noise’?
Random variation in motor and sensory signals due to the fact that the action potential sent along neurons is a crude digital signal
What is ‘redundancy’?
Goal-directed movements can be carried out in several different ways, using different combinations of movements. Repeated efforts to make the same movement are not identical.
The brain must decide which combination is suitable at that point in time.
What are the biological delays?
There are delays in:
- transduction
- conduction of action potentials
- force generation
To produce accurate movement you need to specify when the force reaches its peak.
How fast do eye muscles contract?
20ms to reach peak force
How fast do limb muscles contract?
30 - 50ms to reach peak force
What is ‘non-linearity’?
Mixing individual motor commands does not produce predictable results.
Force depends on length of muscle, load, velocity of shortening, etc.
What is ‘non-stationarity’?
Behaviour of motor systems can change over time
What is thixotropy?
Muscle contraction depends on history
How many motorneurons innervate a muscle?
Hundreds
How many synapses does each motorneuron receive?
30,000 approx
What is the EPSP of one excitatory synapse?
0.1mV approx
What is the spike threshold?
> 10mV depolarisation
What are the disadvantages of negative feedback?
Time delays in feedback loop mean that data can be out of date by the time it reaches the CNS so corrective movements that are generated are inappropriate
This leads to instability and oscillations (cold shower phenomenon)
What are open-loop systems?
Feedforward systems that utilise anticipatory control where sensory information is used to generate a prediction of what is needed in the future
They need to learn; this is guided by comparing desired and achieved outcomes
What is the inverse model?
- Uses desired outcome as starting point
- Joints that need to be moved
- Forces needed to move these joints
- Motorneuron activity needed to create these forces
- THUS commands needed to generate movement
Only useful if accurate so it needs to learn
How do feedforward models learn?
Comparison of intended motion and achieved motion
What is the forward model?
- Predicts consequences of motor commands before and during movement
- Receive information on what motor commands are via efference copy and internal feedback
- Use this information to simulate the response of the motor system and predict the movement
- Prediction compared to desired result
- Corrections set up for errors as they are being made
What are the centres for feedforward control?
- Cerebellum
2. Motor cortex
