Reflex arc

Reflex actions

There are different types of neurones that work together in a reflex action.

This creates an automatic and rapid response to a stimulus, which minimises any damage to the body from potentially harmful conditions, such as touching something hot.

A reflex action follows this general sequence and does not involve the conscious part of the brain, which makes it much quicker.

Diagram of how information flows from receptors to effectors in the nervous system

The nerve pathway followed by a reflex action is called a reflex arc. For example, a simple reflex arc happens if we accidentally touch something hot.

The nerve pathway in the arm
  1. Receptor in the skin detects a stimulus (the change in temperature).
  2. Sensory neurone sends electrical impulses to relay neurone. Relay neurones are located in the spinal cord. They connect sensory neurones to motor neurones.
  3. Motor neurone sends electrical impulses to an effector.
  4. Effector produces a response (muscle contracts to move hand away).

A magnified view of two neurons and a synapse

Where two neurones meet there is a small gap, a synapse.

  1. An electrical impulse travels along the first axon.
  2. This triggers the nerve-ending of a neurone to release chemical messengers called neurotransmitters.
  3. These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the second neurone.
  4. The receptor molecules on the second neurone bind only to the specificneurotransmitters released from the first neurone. This stimulates the second neurone to transmit the electrical impulse.