Describe the mechanism of a reflex action.

A receptor detects a stimulus and generates electrical signals which are conducted by the neurones in the reflex arc. Firstly, the sensory neurone conducts the signal to the spinal cord. There is then a synapse between the neurones in which neurotransmitters are released and stimulate the impulse in the next neurone which is the relay neurone. The same thing then occurs between the relay neurone and the motor neurone. The effector then carries out the response to the stimulus ( e.g. a muscle contracts).