Neurones

• The human nervous system consists of:

  • the central nervous system (CNS) - the brain and spinal cord
  • the peripheral nervous system - nerve cells that carry information to or from the CNS
• All control systems include:

  • cells called receptors, which detect stimuli (changes in the environment)
  • the coordination centre, such as the brain, spinal cord or a gland such as the pancreas, which receives and processes information from receptors around the body
  • effectors bring about responses, which restore optimum levels, such as core body temperature and blood glucose levels. Effectors include muscles and glands, and so responses can include muscle contractions or hormone release
• Nerve cells are called neurones. They are adapted to carry electrical impulses from one part of the body to another. A bundle of neurones is called a nerve.
• Three main types of neurone:

  1. sensory neurones
  2. relay neurones
  3. motor neurones
• Features neurones have in common:

  • the cell body that contains the nucleus, organelles and most of the cytoplasm of the neurone
  • one or more dendrons, which carry nerve impulses towards the cell body, and an axon, a single fibre that carries nerve impulses away from the cell body
  • a fatty, myelin sheath, that covers and insulates the neurone
• Sensory neurones

  • carry electrical signals - nerve impulses - towards the CNS
  • the signal starts in a receptor which detects a change
• Relay neurones

  • carry nerve impulses within the CNS
• Motor neurones

  • carry nerve impulses away from the CNS
  • the neurone ends in either a muscle or gland, which are effectors
• Receptors to effectors : Coordination system


  stimulus -> receptor -> coordinator -> effector -> response
• Receptors to effectors: Nervous system


  receptors (eg sense organs) -> sensory neurones -> CNS -> relay neurones -> motor neurones -> effectors (eg muscles, glands)
• A synapse is a tiny gap at the junction between two nerve cells, which nerve signals must cross.
• When a nerve impulses travels from one neurone to another:

  1. an electrical impulse travels along the first neurone
  2. when it reaches the end of the neurone, chemical transmitter molecules called neurotransmitters are released
  3. the neurotransmitters diffuse across the synapse and bind with receptor molecules on the membrane of the second neurone
  4. this stimulates the second neurone to transmit the electrical impulse