What is a reflex action?

A reflex action is the body's rapid, involuntary response to external stimuli, often used in order to protect it from immediate harm. First, a receptor detects a stimulus, such as a heat source which could burn the skin. A nerve impulse is then passed along the sensory neurone from the receptor to the central nervous system (the spinal cord). The impulse is transferred via a synapse (a gap between two neurones) to a relay neurone within the cord, and then on to a motor neurone via a second synapse. The impulse travels along the motor neurone to an effector (such as a muscle or gland) which brings about the desired response i.e a muscle moving a body part away from the heat source in the burning example .