PHSI2005 Study Guide - Final Guide: Withdrawal Reflex, Stretch Reflex, Motor Neuron
15 May 2018
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Lecture 3: Motor reflexes
Reflex: any long-distance pathway that receives input about change, integrates information & uses the
nervous, endocrine system (or both) to react appropriately
Neural reflex
• Reflex that is inbuilt or acquired (i.e. conditioned reflex)
• Triggered by stimulation of sensory receptor that transmits an AP via sensory neuron to CNS, where it
synapses with multiple neurons in spinal cord
Ways of classifying reflexes
• Motor & autonomic reflexes: reflexes subdivided according to efferent division that controls the effectors
• Integrating region within the CNS (spinal instead of brain)
• Time at which reflex develops (acquired or inbuilt)
• Number of neurons in the pathway (monosynaptic vs polysynaptic)
Motor reflex
• Reflexes where response is driven by motor nervous system (either flexor or stretch reflex)
• Central & peripheral inputs at the dendrites and soma of α-motor neuron: can be either inhibitory post
synaptic potentials (IPSP) or excitatory potentials (EPSP)
• Generation of IPSP or EPSP will determine if an action potential will be triggered in axon hillocks of
motor neuron
The tonic vibration Reflex
• Muscle spindle continuously activated in response to frequent vibrations à continuous contraction
• The muscle will then remain contracted until vibratory stimulus is removed
Document Summary
Reflex: any long-distance pathway that receives input about change, integrates information & uses the nervous, endocrine system (or both) to react appropriately. Neural reflex: reflex that is inbuilt or acquired (i. e. conditioned reflex, triggered by stimulation of sensory receptor that transmits an ap via sensory neuron to cns, where it synapses with multiple neurons in spinal cord. The tonic vibration reflex: muscle spindle continuously activated in response to frequent vibrations continuous contraction, the muscle will then remain contracted until vibratory stimulus is removed. It also synapses with a spinal interneuron that inhibits activity of motor neurons innervating the antagonistic muscles (e. g. hamstring: sensory info also ascends to higher centers via interneurons. *in everyday life, this reflex helps maintain upright posture. Autonomic reflex: similar to polysynaptic reflex: has multiple synapses in cns, different: has 2 efferent autonomic neurons in series, a pre-ganglionic autonomic neuron from the cns synapses with post-ganglionic autonomic neuron in autonomic ganglion.
