nervous system

• nerve cell

  Nerve cells are called neurones. They are adapted to carry electrical impulses from one place to another. A bundle of neurones is called a nerve.

  
• type of neurone

  • sensory
  • motor
  • relay
• They have some features in common:

  • A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.
  • Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.

  
• Key fact

  Stimulus → receptor → coordinator → effector → response
• What is the small gap called where two neurones meet?

  Synapse
• What happens to the electrical signal at the synapse?


  It is converted into a chemical signal.
• How is the chemical signal converted back at the synapse?

  It is converted back to an electrical signal on the other side of the synapse.
• What travels along the first axon?

  An electrical impulse
• What triggers the nerve-ending of a neurone to release neurotransmitters?

  The electrical impulse traveling along the axon.
• What are the chemical messengers released by neurones called?

  Neurotransmitters
• What happens to neurotransmitters after they are released into the synapse?

  They diffuse across the synapse and bind with receptor molecules on the second neurone.
• How do receptor molecules on the second neurone interact with neurotransmitters?

  They bind only to specific neurotransmitters released from the first neurone.
• What is the result of the binding of neurotransmitters to receptor molecules on the second neurone?


  It stimulates the second neurone to transmit the electrical impulse.
• Receptors to effectors

  Receptor cells detect a change in the environment (a stimulus) and start electrical signals along neurons. These move towards the central nervous system (CNS). The CNS is the brain and spinal cord. It coordinates the responses. Messages are then sent back along different neurones to muscles which contract or relax, and glands which secrete hormones. Muscles and glands are called effectors.