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Organization of the Motor SystemA. Closed-loop
1. triggered directly by sensory input2. reflexive
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Organization of the Motor SystemB. Open-loop
1. triggered by a sensory cue or voluntary desire2. volitional, originating in cerebral cortex
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Organization of the Motor SystemC. Level 1
1. initiation, planning, programming2. response to a desire to move3. basal ganglia and cortical projection areas
SMA, PMC4. prefrontal cortex
Organization of the Motor SystemC. Level 1
5. damage to basal ganglia and cortical projection sitesa. does not produce weaknessb. can result in abnormal involuntary movements
chorea: irregular, rapid, uncontrolled, involuntary, excessive movement that seems to move randomly from one part of the body to another.
dystonia: sustained muscle contractions cause twisting and repetitive movements or abnormal postures.
ballismus: jerky or shaking movements of the arms or legs, especially such movements occurring in chorea.
c. Parkinson’s disease
Organization of the Motor SystemD. Level 2
1. cerebellum2. coordination of movements3. is a comparator4. stores a lot of muscle memory
5. damage- so motor pathways can “remember” how to perform actions
does not cause weaknessloss of coordination
Organization of the Motor SystemD. Level 3
1. origin of descending motor pathwaysa. corticospinals/pyramidal tractsb. extrapyramidal tracts
- originate from subcortical structures
2. damage- still receive an input from the primary motor cortex (MsI)
- weakness- increased tone- hyperreflexia
Organization of the Motor SystemD. Level 4
1. spinal cord interneurons- some mediate spinal cord reflexes
2. central pattern generators- spinal interneurons capable of generating their own inputs to motor neurons (independent of any input)
Organization of the Motor SystemD. Level 5
1. lower motor neurons- is the output to the skeletal muscle
2. receives input from the muscle spindle and Golgi tendon organs3. center for simple stretch reflexes of muscles4. damage
- weakness- wasting- hypotonia- weak or areflexic QuickTime™ and a
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Ia afferent nerves (from spindle)
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Lateral = distal (typically)Ventral = axial & proximal
Ventral anterior horn = extensor musclesDorsal anterior horn = flexor muscles
Propriospinals connect the motor neuron poolsPropriospinals also connect the CPGs
Humans cannot typically locomote in the absence of significant supraspinal inputs (no fictive locomotion)
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