Reflex Arc

• A reflex action is an involuntary, quick action to respond to a stimulus, in order to protect the body from danger E.g. quickly removing your hand from hot metal surface
• Reflex actions involve three neurones: a sensory neurone, relay neurone and motor neurone.
• The gap between neurones is called a synapse.
• How the reflex arc works:

  • A stimulus affects a receptor
  • A sensory neurone carries impulse from the receptor to the CNS
  • Connector / relay neurone carries impulse slowly (because it has no myelin sheath) across the spinal cord
  • Motor neurone carries impulse from the CNS to the effector
  • Effector (either a muscle or a gland) carries out the response

  
• Receptor: cell or organ that converts a stimulus into an electrical impulse
• Reflex action: means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)