homeostasis

• Control systems

  Include cells called receptors, coordination centre (e.g., brain, spinal cord, pancreas), and effectors that bring about responses to restore optimum levels
• Nerve cells

  Also known as neurones, adapted to carry electrical impulses from one place to another
• Bundle of neurones

  Called a nerve
• Main types of neurones

  • Sensory
  • Motor
  • Relay
• Neurones

  • Have a long fibre (axon) insulated by a fatty sheath (myelin), tiny branches (dendrons) branching further as dendrites at each end
• Information flow in the nervous system

  Stimulus → receptor → coordinator → effector → response
• Receptors are groups of specialised cells that detect changes in the environment (stimulus) and stimulate electrical impulses in response
• Sense organs contain groups of receptors that respond to specific stimuli
• Effectors include muscles and glands that produce a specific response to a detected stimulus
• At a synapse, where two neurones meet, a small gap exists
• Transmission of electrical impulses at a synapse

  Electrical impulse travels along the first axon, triggering the release of neurotransmitters from the nerve-ending of a neurone, which diffuse across the synapse and bind with receptor molecules on the membrane of the second neurone, stimulating the second neurone to transmit the electrical impulse
• Sensory neurone

  Sends electrical impulses to relay neurone, located in the spinal cord, connecting sensory neurones to motor neurones
• Motor neurone

  Sends electrical impulses to an effector
• Effector

  Produces a response (e.g., muscle contracts to move hand away)