Describe which neurones are involved in coordinating a reflex action.

Reflexes are involuntary and instantaneous actions that occur in response to a stimulus, for example our pupils contracting in response to a bright light. The receptor detects this stimulus and sends an electrical impulse down the sensory neurone. The sensory neurone conducts this signal down to its synapse with the relay neurone in the spinal cord. Neurotransmitters at the synapse then stimulate the relay neurone. The relay neurone then has another synapse with the motor neurone. Once again neurotransmitters stimulate the next neurone and the electrical impulse is sent down the motor neurone. The motor neurone then causes the response.In our example, the eye detects the light stimulus, sending an impulse down the sensory neurone to the spinal cord. Here the relay neurone communicates this signal between the sensory and the motor neurone. The motor neurone sends the signal back to the eye causing the muscles to contract, thus constricting the pupil.