MRI scan of the brain

White and grey

Inside the brain, only white and grey matter

The brain is made of grey and white matter. Grey matter contains the cell bodies of neurons (nerve cells) and their local connections to each other. White matter contains bundles of nerve fibres that connect distant brain regions to one another; it gets its name from the fatty myelin that insulates the axons, which makes the tissue look white to the naked eye.

The brain contains 86 billion neurons. They are specialised to produce electrical impulses called action potentials. Neurons use a change in the number of action potentials that they ‘fire’ to change the information they are transmitting. Neurons form intricate networks and communicate with each other across junctions called synapses. Action potentials cause the neuron on one side of the synapse to release a neurotransmitter that travels across the synapse to the neuron on the other side. Receptor proteins detect the neurotransmitter and generate new action potentials in response.

Lead image:

An MRI scan of a healthy adult brain taken from behind, showing white and grey matter structures.

Dr Flavio Dell'Acqua/Wellcome Images CC BY


About this resource

This resource was first published in ‘Inside the Brain’ in January 2013 and reviewed and updated in November 2017.

Inside the Brain
Education levels:
16–19, Continuing professional development