Structure & Function (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Nervous system: Basics

• The human nervous system consists of:

  • the Central nervous system (CNS) - the brain and spinal cord

  • the 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

Diagram of the structure of the nervous system

Use this image

Structure of the nervous system

• Receptors detect stimuli in the environment

• Information from receptors passes along cells (neurones) as electrical impulses to the central nervous system (CNS)

• The CNS comprises the brain and spinal cord

• The CNS is the coordinator between receptors and effectors, such as muscles contracting or glands secreting hormones

• The pathway through the nervous system is:

stimulus → receptor → coordinator → effector → response