Structure & Function (AQA GCSE Biology: Combined Science)

• 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 is comprised of the CNS and the PNS

• 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