Describe the process of the reflex arc.

The reflex arc is activated to create a rapid response in order to maintain safety. It is an innate, automatic response to a dangerous stimulus.

It involves 3 neurones. A sensory neurone, a motor neurone and a relay neurone. 

Firstly a receptor is stimulated by a stimulus, e.g. in your hand when touching a flame. This causes an impluse to be sent down the sensory neurone. This synapses with a relay neurone that is responsible for sending the impulse to the central nervous system that coordinates the response. The relay neurone will deliver this response to the motor neurone it synapses with, causing a signal to be sent to an effector, generally a muscle. This causes a response in the effector, e.g. contraction of the muscle, pulling it away from the hot flame.