what is reflex arc

A reflex arc is a neural pathway in the nervous system that controls a reflex, which is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus. The primary components of a reflex arc are the sensory neurons (or receptors), interneurons (or adjustors), and effectors. The sensory neurons receive stimulation and connect to other nerve cells that activate muscle cells (or effectors), which perform the reflex action. The simplest arrangement of a reflex arc consists of the receptor, an interneuron, and an effector, which form a functional group. Sensory cells carry input from the receptor (afferent impulses) to a central interneuron, which makes contact with a motor neuron. The motor neuron carries efferent impulses to the effector, which produces the response. Three types of neurons are involved in this reflex arc, but a two-neuron arc, in which the receptor makes contact directly with the motor neuron, also occurs. Simple reflexes are prompt, short-lived, and automatic. Reflexes are found with varying levels of complexity in organisms with a nervous system, and they are fine-tuned to increase organism survival and self-defense.