Reflex actions

A reflex action is an automatic and rapid response to a stimulus - we do not have to think about a response. Reflex actions minimise damage to the body from potentially harmful conditions, such as touching something hot.

Different types of neurones work together in a reflex action. A reflex action follows this general sequence:

Neurones work together to make a reflex action

The nerve pathway followed by a reflex action is called a reflex arc.

A simple reflex action happens if we accidentally touch something hot. We rapidly move our hand away. This is called the pain withdrawal reflex.

The diagram shows the reflex arc involved.

The nerve pathway in the arm
  1. The receptor in the skin detects a stimulus - the change in temperature.
  2. The sensory neurone sends nerve impulses to the spinal cord.
  3. The relay neurone, which is located in the spinal cord, carries the nerve impulses from sensory neurones to motor neurones.
  4. The motor neurone sends nerve impulses to the effector.
  5. The effector - the biceps muscle in the arm - contracts so that the hand is moved away.