What is reflex action? We can understand it simply with this question. What happens when we accidently place our hand on a pin?
Answer: We move away our hand instantly.
This action, that our body performs automatically when there is an emergency is known as reflex action. It occurs quickly and unconsciously. In a reflex action, the messages are received by the spinal cord, and a quick decision is taken by the spinal cord about what to do and it quickly informs the body-part. These actions are involuntary. In the spinal cord, the nerve impulses move from sensory neurons to the interneurons (also known as relay neurons). The impulses are then sent to motor neurons which project out of the spinal cord to stimulate your muscles (effector) in order to contract, hence snatching your hand away from the hot pot. This is known as a ‘reflex arc’. This process happens so fast that the response occurs before the message reaches the brain or the message may not be sent to the brain at all.