What is a reflex arc?

The three different types, sensory, relay and motor neurons can all be used in a reflex arc; a relay neuron is not always necessary but often is included. It is easiest to remember them in that order as that is the order they generally are in a simple reflex arc. A SENSory neuron receives (SENSES) the stimuli using sensory cells. The relay neuron relays that impulse (carries it on) from the sensory to the motor neuron. Lastly the motor neuron carries the impulse to the target and creates a response via the effector. There also have to be sensory cells, e.g pacinian corpuscle cells in the skin that detect changes in pressure, and an effector, e.g a muscle which moves the part of the body being affected. An example of a reflex arc is when your hand touches a hot pan the thermoreceptors in the skin detect the change in temperature, the energy from this is larger than the threshold potential so releases an action potential which is passed down the sensory neuron as an impulse. Then this is conducted by the relay neuron which leads to the motor neuron, at the end of the motor neuron the action potential arrives at the effector muscle, e.g a muscle in the arm, causing the muscle to contract and bring your hand away from the hot pan. This series of events is known as a reflex arc.