Reflex Arc | Biology for Grade 10 PDF Download

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.
  
• 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.
  
  • Receptor in the skin detects a stimulus (the change in temperature).
  • Sensory neurone sends electrical impulses to relay neurone, which are located in the spinal cord. They connect sensory neurones to motor neurones.
  • Motor neurone sends electrical impulses to an effector.
  • Effector produces a response (muscle contracts to move hand away).
• Where two neurones meet there is a small gap, a synapse.
  
  • An electrical impulse travels along the first axon.
  • This triggers the nerve-ending of a neurone to release chemical messengers called neurotransmitters.
  • These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the second neurone.
  • The receptor molecules on the second neurone bind only to the specific neurotransmitters released from the first neurone. This stimulates the second neurone to transmit the electrical impulse.