Structure & Function

• The human nervous system consists of the Central nervous system (CNS) which includes the brain and spinal cord, and the Peripheral nervous system (PNS) which includes 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 which are electrical signals that pass along nerve cells known as neurones.
• A bundle of neurones is known as a nerve.
• 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).
• Having long axons is more efficient than having multiple neurones to convey information from the CNS to effectors as 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.
• 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.