organization of the motor system a. closed-loop 1. triggered directly by sensory input 2. reflexive

Organization of the Motor SystemA. Closed-loop

1. triggered directly by sensory input2. reflexive

QuickTime™ and aTIFF (Uncompressed) decompressor

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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



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


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


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)


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)

Bag 1: rate changeBag 2: absolute length

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)



Remember: almost all motor tracts are crossed.

organization of the motor system a. closed-loop 1. triggered directly by sensory input 2. reflexive

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