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EX1: motor system
COGN MOTOR SYSTEM
| Term | Definition |
|---|---|
| 3 main components of motor system (motor hierarchy) | lower motor neurons, upper motor neurons, extrapyramidal system |
| Lower motor neurons (final common pathway) | spinal reflexes, cranial nerves, skeletomuscular efferents, autonomic efferents |
| Upper motor neurons (descending control) | pyramidal (primary) motor system, brainstem systems: provides descending control over lower motor neurons and spinal reflexes |
| Upper motor neurons anatomy | |
| coded in primary motor cortex | Target brainstem/spinal cord interneurons for multijoint, complex movements: Codes magnitude and direction of force to be exerted, Direction of visually guided movements determined by population coding |
| Upper Motor Neuron Syndromes | Somatotopic paresis (weakness/hypotonia), babinski sign, • Spasticity/decerebrate rigidity, Hyperreflexia of sensory-motor reflexes, Loss of fine movement control with lateral corticospinal damage |
| Parietal cortex | transforms sensory inputs into a body-centric space to guide action |
| Damage to parietal cortex | can disrupt goal-directed reaching and eye movements |
| lateral premotor cortex | initiates externally-guided motor movements, signals intention to make a particular movement in response to a sensory cue (planning, selection) |
| medial premotor cortex (supplementary motor cortex) | initiates internally guided motor movements, damage reduces self-initiates movements |
| premotor cortex (BA 6) | neurons respond maximally during movement planning, activation is greater for self-initiated vs. visually triggered |
| readiness potential (scalp EEG) | precedes both intentions and actions, starts out anterior and bilateral (premotor) then shifts posterior and contralateral (motor): enhanced when attention is focused on motivations to act controversial: debate over whether we have free will over action |
| basal ganglia anatomy | 4 main components: neostriatum (corpus striatum), paleostriatum (globus pallidus), subthalamus, substantia nigra (midbrain) |
| basal ganglia processing output | globus pallidus internal (GPi)/Substantia Nigra pars reticulata, output is inhibitory (GABA) with high resting activity |
| info processing in basal ganglia | projects to thalamus and superior colliculus, disengagement of output neurons needed to release goal directed movements in direct pathway |
| cortico-striatal-thalamic loops | ex: motor loop, interface with upper motor and oculomotor neurons |
| direct vs. indirect pathways (car analogy) | indirect involves subthalamus which serves as "brake" on disinhibition from direct pathways, direct pathways are accelerator |
| hemiballismus | disease of subthalamus, removes "brake" of indirect pathway resulting in spontaneous uncontrolled movements on contralateral side |
| parkinsons disease | DA nigrostriatal pathway degenerates (50-80%), which increases inhibitory outflow to thalamus by synergistic actions on direct and indirect pathways causing negative motor symptoms |
| parkinsons treatments | behavioral: use external sensory cues to help initate movements pharacologic: replace DA: L-DOPA (problems are blood brain barrier and non specificity implanted deep brain stimulators |
| huntingtons disease | progressive degernative disorder, late adult onset, inherited, loss of medium spiny neurons that project to Globus Pallidus external (indirect pathway)- cannot apply the brake: movement is less goal oriented, loss of sustained muscular contraction |
| cerebellum | 2 main components: nuclear group/deep nuclei (output), cortex |
| cerebellum cortex | anterior lobe, flocculondular lobe, lateral lobes |
| anterior lobe (cerebellum) | spinocerebellum (muscle tone/reflexes): vermis, paramedian zone |
| flocculonodular lobe (cerebellum) | vestibulocerebellum (Balance) |
| lateral lobes (cerebellum) | cerebrocerebellum (sensorimotor coordination/timing/errors) |
| body representation in cerebellum | ipsilateral (spinocerebellar and vestibular axons dont cross, descending projections from ctx cross in peduncles and then cross back) |
| motoric consequences of damage to the lateral cerebellar cortex (neocortical) | ataxia (clumsy), hypermetria (rapid pointing movements extend beyond target, problems switiching between gestures, poorly timed movements, abnormal reflex conditioning/motor learning |
| error correcting role of cerebellum | involving in on-line and feedback based guidance of movement trajectories and movement correction following termination |
| cerebellar vs. basal ganglia loops | externally guided vs. internally guided sequences/target actions termination (correction) vs. initiation of movements interaction of each level of motor processing for different aspects of action |
Created by:
justinem
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