Reflexes / Withdrawal reflex
Withdrawal reflex
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polysynaptic reflex
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occurs in response to noxious (usually painful) stimulation - response is contraction of flexor muscles and inhibition of extensor muscles, so that stimulated part is withdrawn from the stimulus
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this occurs through the process of RECIPROCAL INHIBITION: collateral branches of the Ia afferent fibres synapse on inhibitory interneurons that suppress the activity of alpha motor neurons that innervate antagonist muscles
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- if the part is a limb, the response includes extension of the opposite limb (the crossed extensor response)
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the spread of excitatory impusles up and down the spinal cord to activate more motor neurons is called irradiation of the stimulus, and this process results in recruitment (it results in an increase in the number of active motor units)
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- stronger stimuli produce greater flexion and shorter reaction times, sometimes producing a series of movements due to prolonged, repeated firing of the motor neurons (after-discharge)