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.
An anatomical illustration of the human body showcasing the nervous system. The brain is highlighted in a light orange colour, from which the spinal cord descends in a straight line down the back. Branching out from the spinal cord and extending to various parts of the body are numerous blue nerves representing the Peripheral Nervous System (PNS). Two circular labels, one red and one blue, both indicate "PNS - Peripheral nervous system" and are placed adjacent to the branching nerves. The overall colour scheme includes shades of blue, orange, and red against a white background.


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

An illustrative depiction of a neuron, with its central cell body coloured in shades of brown. From the cell body extend multiple branching structures, known as dendrites. The central part of the cell body is marked as the nucleus, which emits a subtle glow. Emerging from the opposite side of the cell body is a long, tube-like structure called the axon, which is segmented in appearance and ends in finer branches termed nerve endings. Various parts of the neuron, including the dendrites, nucleus, cytoplasm, axon, and nerve ending, are clearly labelled with blue arrows pointing to them. The backdrop is white, highlighting the intricacy of the neuron's structure.

  • 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