The Human Nervous System

The nervous system detects stimuli, which helps us react and adapt to changes in our environment. It consists of:

  • Central nervous system (CNS) – The spinal cord and the brain
  • Peripheral nervous system (PNS) – The part of the nervous system outside the central nervous system. It carries information to and from the central nervous system.


Neurones, also known as nerve cells, are specialised cells which have adapted to carry electrical impulses.

  • A nerve is made up of a cluster of neurons

Axons have a long, thin structure, insulated by the fatty myelin sheath, with certain sections not insulated, known as nodes.

Axons carry messages throughout the body, which are then received by extensions called dendrites. This means that neurones are connected to each other by a network, allowing for easy communication.

Receptors detect stimuli and send electrical impulses along neurones to the central nervous system (which is the coordination centre). After this, electrical impulses are sent via neurones to effectors, which produce a response.

  • Effectors are just parts of the body that produce a response, for example, muscles (which contract) or glands (which secrete substances).

Therefore, the path through the nervous system is:

Stimulus → receptor → coordinator → effector → response