How does the reflex arc work?

first something must occur, a change in the external environment (and more rarely within the body). This is known as a stimulus.This stimulus will be picked up or "recepted" by a receptor.The receptor then forms an electrical signal which is passed onto the sensory neurone which conducts the electrical signal to the relay neurone which is part of the central nervous system (CNS).From the relay neurone the electrical signal is passed on to the motor neurone, which is then passed on to the effector which may be a gland to release a hormone (chemical message) or a muscle to respond appropriately to the stimulus.
Between each neurone there is a gap known as a synapse. here the electrical signal is converted into a chemical messenger to travel through this gap. Once it has reached the new neurone it will again be reconverted to an electrical signal.
Only the relays neurones are found in the central nervous system which is made up of the brain and the spinal cord whilst the motor and sensory neurones are found tin the peripheral nervous system.