AQA GCSE Biology

Revision Notes

5.2.1 Structure & Function

Nervous System: Basics

  • The human nervous system consists of:
    • Central nervous system (CNS) – the brain and spinal cord
    • Peripheral nervous system (PNS) – all of the nerves in the body
  • The nervous system enables humans to react to their surroundings and to coordinate their behaviour
  • Information is sent through the nervous system as electrical impulses – electrical signals that pass along nerve cells known as neurones
  • A bundle of neurones is known as a nerve

Adaptations of the nervous system

  • Neurones have a cell body (where the nucleus and main organelles are found) and cytoplasmic extensions from this body called axons and dendrites
  • Some human neurones have axons over a metre in length (but only 1 – 4 micrometres wide)
  • This is far more efficient than having multiple neurones to convey information from the CNS to effectors – less time is wasted transferring electrical impulses from one cell to another
  • The axon is insulated by a fatty myelin sheath with small uninsulated sections along it (called nodes) which the impulse jumps along

The human nervous system, IGCSE & GCSE Biology revision notes

The human nervous system is comprised of the CNS and the PNS

Structure of the Nervous System

  • Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS)
  • The CNS is the brain and spinal cord
  • The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones
  • The pathway through the nervous system is:
stimulus → receptor → coordinator → effector → response

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