nerves and reflexes

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  • nerves and reflexes
    • stimuli are detected by sensory receptors that send impulses along sensory neurones to the central nervous system
    • neurones are specialised cells that carry nervous impulses
    • types of neurones
      • sensory neurones carry impulses to the central nervous system
      • motor neurones carry impulses from the central nervous system to effector organs
      • relay neurones are found only in the central nervous system
      • 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.
    • the coordination centre, such as the brain, spinal cord or pancreas, receive and process 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 so responses can include muscle contractions or hormone release
    • the point where two neurones meet is called a synapse
      • there is a small gap between the neurones
        • the electrical nerve impulses can not be carried across the gap so the impulse is carried by neurotransmitters
    • receptors to effectors
      • Receptor cells detect a change in the environmental (a stimulus) and start electrical signals along neurons. These move towards the central nervous system (CNS).
        • 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.
      • Receptors are groups of specialised cells.
        • They detect a change in the environment and stimulate electrical impulses in response.
      • Effectors include muscles and glands. They produce a specific response to a detected stimulus.
    • the relax arc
      • reflex arcs involve only three neurones and impulses pass to and from the spinal cord
        • this provides a fast response that does not involve the brain
      • relaxes help protect us from immediate harm such as eye blink relax which protects the eye if something comes close to it


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