• There are?three main types?of neurone:?sensory, relay and motor
  • Sensory?neurones carry impulses from?receptors?to the Central Nervous System (CNS?- the brain or spinal cord)
  • Relay?(intermediate) neurones are found entirely within the CNS and?connect?sensory?and?motor?neurones
  • Motor?neurones carry impulses from the?CNS?to?effectors?(muscles or glands)

   

• Sensory?neurones,?relay?(intermediate) neurones and?motor?neurones work together to bring about a?response?to a?stimulus
• A?reflex arc?is a?pathway?along which impulses are transmitted from a receptor to an effector?without involving ‘conscious’ regions of the brain
• As it does not involve the brain, a reflex response is?quicker?than any other type of nervous response
• Examples of simple reflex actions that are coordinated by these pathways are:
  • Removing the hand rapidly from a sharp or hot object
  • Blinking
  • Focusing the eye on an object
  • Controlling how much light enters the eye

   

How sensory neurones, intermediate (relay) neurones and motor neurones work together to carry out a reflex action

• In the example above:
  • A pin (the?stimulus) is detected by a pain?receptor?in the skin
  • The?sensory?neurone?sends electrical?impulses?to the spinal cord (the?coordinator)
  • Electrical impulses are passed on to?relay?neurone?in the spinal cord
  • The relay neurone connects to the?motor neurone?and passes the impulses on
  • The motor neurone carries the impulses to the muscle in the leg (the?effector)
  • The impulses cause the muscle to contract and pull the leg up and away from the sharp object (the?response)

   

The pathway of a reflex arc