1-7. REFLEX ARC

An impulse follows a conduction pathway from its origin in the dendrites or neuron cell body in one part of the body to the impulse's end somewhere else in the body. One pathway is called a reflex arc and is a functional unit of the nervous system. The basic parts of a reflex arc are a receptor, a sensory neuron, a center, a motor neuron, and an effector.

a. Function of Components of a Reflex Arc. Functions are:

(1) Receptor. The receptor activates a nerve impulse in a sensory neuron in response to a change in the body's internal or external environment.

(2) Sensory neuron. This neuron conducts the impulse from the receptor to its axonal end in the central nervous system.

(3) Center. This is a receiving area (usually in the central nervous system) in which the incoming sensory impulse connects with an outgoing motor impulse. The impulse may be repressed, transmitted, or rerouted in the center area.

(4) Motor neuron. The job of the motor neuron is to transmit the impulse to the proper body organ.

(5) Effector. The effector is the organ of the body that responds to the impulse from a motor neuron. An effector may be either a muscle or a gland.

Figure 1-4. The pathway of an impulse over the reflex arc.