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Lesson 9. Reflex Arc

2-9. REFLEX ARC

The simplest reaction of the human nervous system is the reflex. A reflex is an automatic reaction to a stimulus. The pathway from the receptor organ to the reacting muscle is called a reflex arc (figure 2-5). The pathway of a reflex arc contains five components.

Figure 2-5. Reflex arc.

a.      The stimulus is received by a receptor organ specific to that stimulus.

b.      The information is transmitted to the CNS by the afferent neuron of the appropriate peripheral nerve.

c.      Within the spinal cord, the afferent neuron synapses with a special connecting neuron called the internuncial neuron (or interneuron).

d.      In turn, the internuncial neuron synapses with the efferent neuron's cell body. The axon of the efferent neuron carries the information to the effector organ.

e.      The effector organ receives the command to act.

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