Grey matter versus white matter
Grey matter holds neuronal cell bodies, dendrites and synapses, while white matter is the pale tissue rich in axons that carries signals between regions.
Remember
Grey matter is where cell bodies, dendrites and synapses are found, and it has a rich blood supply. White matter is mainly axons, and its myelin makes it pale.
Memory aid
grey matter is where nerve cells gather and the work is done; white matter is the wiring between the work sites.
Picture grey matter as the work sites where nerve cells gather and white matter as the wiring that links those sites.
Grey matter and white matter are the two kinds of tissue in the central nervous system, and which one a portion is depends on the cell types it contains. Grey matter contains neuronal cell bodies, dendrites (the branches that receive signals), axons and synapses (the junctions where neurones pass signals on), together with blood vessels. It forms the cerebral cortex, the folded sheet on the surface of the brain, and also deep clusters called nuclei.
White matter lies beneath the cerebral cortex and is rich in axons, many of them myelinated. Myelin is a fatty insulating sheath. It gives white matter its pale colour and speeds up the signals it carries between regions.
Grey matter has a higher density of small blood vessels than white matter and uses oxygen at a much higher rate. Because grey matter uses oxygen at such a high rate, it is vulnerable to ischaemia when its blood flow falls.
The cerebellum follows the same plan as the cerebral hemispheres, with grey matter on its surface and white matter inside. In the spinal cord the reverse holds: white matter forms an outer shell around a central core of grey matter.
The peripheral nervous system does not use these terms. It has a ganglion (a cluster of cell bodies) in place of grey matter and a nerve (a bundle of axons) in place of white matter.
Key facts
- Grey matter
- holds neuronal cell bodies, dendrites and synapses, and has a higher density of small blood vessels than white matter.
- White matter
- is made mainly of axons, many of them myelinated, and the myelin gives it its pale appearance.
- Pattern in the brain
- grey matter forms the cerebral cortex on the surface and the deep nuclei, while white matter lies beneath the cerebral cortex.
- Spinal cord
- the reverse pattern, with a central core of grey matter surrounded by white matter.
- Oxygen use
- grey matter uses oxygen at a much higher rate than white matter.
- Peripheral equivalents
- a ganglion for grey matter and a nerve for white matter.
Exam traps
- White matter does not mainly contain neuronal cell bodies and does not form the surface of the cerebral hemispheres. It is rich in axons and lies beneath the cerebral cortex, which is grey matter.
- White matter is not the more vascular tissue. Blood supply does follow demand, but it is grey matter that has the higher density of small blood vessels and the higher oxygen use.
- Selective myelin damage does not mainly hit grey matter, because grey matter is made mainly of cell bodies, dendrites and synapses, while myelin lies mainly around the axons of white matter.
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