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Neural Circuits
Reflexes & Reflex Arcs
many of the body’s control systems occur at the most basic functional level of neural activity reflexes
reflex = a rapid, automatic, predictable motor response to a stimulus unlearned unplanned involuntary “hard wired” into our neural anatomy
reflex arc = simplest functional circuit in nervous system
components of a reflex arc: receptor sensory neuron integration center (CNS) single or multiple synapses motor neuron effector
very few complete neural circuits are simple reflexes
reflexes can be categorized according to: A. effectors involved B. nerves of PNS that transmit the signal
A. Reflexes based on effectors involved:
1. somatic reflexes involve skeletal muscles we are aware of them (after the fact)
eg. stretch reflex knee-jerk reflex hitting patellar ligament stimulates muscle spindle pulls quadriceps afferent impulses L2-L efferent impulse contraction of quadriceps
eg. withdrawal reflex touching hot skillet pain receptors in skin effectors cause us to pull away from heat
eg. deep tendon reflex eg. crossed extensor reflex
1. autonomic (visceral) reflexes unconscious, usually no awareness most internal homeostatic mechanisms eg. blood pressure, heart rate, vasodilation, etc
B. nerves of PNS that transmit the signal
1. cranial reflexes reflexes that involve cranial nerves 2. spinal reflexes reflexes that involve spinal nerves
some more complex “reflexes” are learned involve more complex circuits in several areas of the brain eg. riding bike, driving skills, swimming, playing piano or musical instruments, gymnastics, etc
remember each neuron synapses with 10,000 other neurons
results in much more complex circuits & interactions than just simple reflexes eg. neuronal pools eg. complex circuits eg. serial circuits eg. parallel circuits
1. serial circuits = input travels along a specific pathway to a specific destination whole circuit works “all-or-none”
eg. spinal reflexes specific stimulus always causes the same motor response
2. parallel circuits =inputs are segregated into many different pathways information is delivered by each pathway and dealt with simultaneously
eg. “smelling a pickle” sensation like/dislike
