Reflex arc

• The nervous system enables humans to react to their surroundings and coordinate their behavior
• The nervous system comprises millions of neurones and uses electrical impulses to communicate quickly
• A reflex action is an automatic and rapid response to a stimulus that minimizes damage to the body from harmful conditions
• Reflex actions do not involve the conscious part of the brain, making them quicker
• The nerve pathway followed by a reflex action is called a reflex arc
• In a reflex arc:

  • Receptor in the skin detects a stimulus (change in temperature)
  • Sensory neurone sends electrical impulses to relay neurone in the spinal cord
  • Relay neurone connects sensory neurones to motor neurones
  • Motor neurone sends electrical impulses to an effector
  • Effector produces a response (muscle contracts to move hand away)
• At the junction between two nerve cells, there is a small gap called a synapse
• An electrical impulse triggers the release of neurotransmitters, which diffuse across the synapse and bind with receptor molecules on the membrane of the second neurone