Site author Richard Steane
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Voluntary and reflex actions



e.g. withdrawal reflex
Initiated in (cerebral cortex of) brain
- due to thought?
Initiated by stimulation of receptor,
e.g. in skin
Impulse passes to motor area (on side of cerebral cortex) and thence down spinal cord to: Impulse passes up dendrite & axon of sensory neurone and on (via synapse) to relay neurone in grey matter near to centre of spinal cord which passes impulse directly and on (via synapse) to :
Motor neurone (cell body in grey matter) carries impulse to effector (muscle) which contracts and produces action
Impulse passes over to opposite side of body,
i.e. left side of brain controls right side of body
(& vice versa)
Stimulus, neurones, action all on same side of body
Many cells & synapses, and longer pathway - therefore slow Only 3 cells, 2 synapses - therefore quicker
Secondary information passes up spinal cord to brain, so subject is aware after the event

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