Download An Introduction to Reflexes

An Introduction to Reflexes
Pages 413 -421
Neuronal Pools: functional groups of neurons.
• Neural Circuit: The pattern of synaptic
connections in a neuronal pool.
– divergent: amplifying circuitry
– convergent: concentrating circuitry
– parallel: multiple circuitry
– serial: reflex circuitry
– reverberation: repeating circuitry
Reflex: rapid, automatic responses to specific
stimuli.
• show little variability
• preserve homeostasis
• exhibit serial circuitry
Reflex Arc: the “wiring” of a single reflex.
• Reflex arcs have five essential
components:
1.
2.
3.
4.
5.
receptor
sensory neuron
CNS integration*
motor neuron
effector
2.
1.
3.
5.
*not all reflexes require CNS integration.
4.
Classification of Reflexes:
• Development
– innate: pre-established
– acquired: learned
• Nature of response
– somatic: involuntary control of skeletal muscles
– visceral: autonomic reflexes
• Complexity of Circuit
– polysynaptic: at least three neurons
– monosynaptic: two neurons
• Processing sight
– spinal: nuclei of spine
– cranial: nuclei of brain
Stretch Reflex: maintenance of appropriate
muscle length.
• monosynaptic
• ipslateral
The stretch reflex is important in maintaining muscle tone, balance, and posture.
Muscle Spindles: proprioceptors
Reciprocal inhibition: inhibition of antagonist muscles (parallel processing)
Withdrawal Reflex: move affected body part
away from stimulus.
• polysynaptic
• ipsilateral
Reciprocal inhibitor (blue neuron):
inhibition of antagonistic muscles.
The withdrawal reflex can be overridden by descending signals from the brain.
Crossed-extensor Reflex: additional motor
response occurs on the side opposite to the
stimulus
• polysynapitc
• ipsilateral withdrawal
reflex.
• contralateral extensor
reflex.
Superficial Reflexes: elicited by gentle
cutaneous stimulation.
Clinical important reflexes for diagnostic testing of motor pathways and
spinal cord reflex arcs.