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Motor systems

Evolution, disease, control

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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