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Motor systems
Evolution, disease, control
| Term | Definition |
|---|---|
| Which animals have a cerebral cortex? | Only mammals have cerebral cortex |
| What are the motor systems for simple vertebrate organisms? | Alternatively activated lateral muscle columns -> rhythmic propulsion -> controlled by local interneuron circuits -> CPG for automatic mvmt |
| What is the evolution for motor systems? | Simple vertebrates -> react to somatosensory inputs (reflex arc) -> sense organs (guided mvmt from brainstem) -> cerebellum/basal ganglia (control brainstem) -> cerebral cortex -> goal-directed mvmt) -> limb development (bypass brainstem) |
| What does disease of the motor neurons/peripheral nerves cause? | Flaccid paralysis -> no force generation due to floppy muscles -> botulinum toxin (cleave synaptobrevin -> no exocytosis of ACh -> no excitatory stimulation) |
| What does disease btwn the brainstem and local spinal circuits cause? | Postural deficits -> unable to erect organism/control eqbm -> inhibit gross whole body mvmt, limited ANS control -> inhibit breathing patterns |
| What does disease btwn the primary motor cortex and local spinal circuits cause? | Spastic paralysis -> uncontrollable continuous muscular contractions -> unregulated force generation -> stroke |
| What does disease of the cerebellum cause? | Ataxia -> poor mvmt coordination -> clumsy, inaccurate, badly timed mvmt |
| What does disease of association motor cortex cause? | Apraxia -> intact cerebellum allows good muscle coordination but mvmt is not purposeful/voluntary |
| What does disease of the basal ganglia cause? | Hyper/hypokinesia -> inability to characterise mvmts -> prolonged/inappropriate |
| What are the advantages of -ve feedback systems? | Automatically compensates for unpredicted deviations from set point (noise) |
| What are the disadvantages of -ve feedback systems? | Limited by feedback loop time delays (sensory receptor -> brain -> muscle -> force), overcorrection from historical error signals (oscillating variable), inappropriate for fast operation (fight/flight, speech cannot wait for slow sensory feedback signals) |
| What is ballistic mvmt? | Set motor commands decided on prior information (memory) -> performed while disregarding sensory information during progress mvmt -> sensory information generates prediction of future requirement |
| What is needed for ballistic mvmt? | Internal model systems -> represent body mechanics among external behaviour -> brain must learn from past experience |
| What is the mechanism of internal model systems? | Receives current sensory signal -> predict future organism behaviour, predict utility of motor commands in environment (mental rehearsal) -> learning by iteration, efference copy for rapid predictions of outcome (internal feedback) -> compared and altered |
| What brain structure is involved in feedforward control? | Cerebellum -> abundant efference copy/internal feedback systems -> useful for fast mvmt involving sequence of elements |
| What is an example of a -ve feedback system? | Stretch reflex -> sensory receptor -> slow A alpha/beta/gamma neuron -> fast A alpha neuron -> effector, pupillary light reflex, moving gaze depth to another object (corrective mvmt = discrepancy size) |
| What are the features of -ve feedback systems? | Mvmts made after error, size of correction = size of error |
| What are the features of +ve feedback systems? | Increase discrepancy of variable to setpoint, size of error proportional to increasing discrepancy |
| What are the features of feedforward systems? | Mvmt in absence of error as correction made before mvmt has occurred |
| What is an example of a feedforward system? | Eye mvmt -> train gaze on moving object -> higher visual processing predicts where pen will be and moves eyeball accordingly, train moving gaze on stationary object -> efference copy of head mvmt (SCM), integrated w/ ocular muscles |
| What is an example of ballistic mvmt? | Nociceptive pain reflex -> fast motor efferent in response to pain stimulus -> no time to analyse mvmt output -> sharp jerking aversive mvmt, side-to-side eye mvmt (no depth change) -> targets in same fixation field |
| What is an efference copy? | Diverted command away from signal to effector -> used for learning, memory, prediction, coordination |
| Compare speed of motoneurons and sensorineurons? | Motoneurons are much faster -> immediately act on already delayed perception of environment |
Created by:
vykleung
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