Gray Matter and White Matter in the Brain

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The brain contains both gray matter and white matter. The gray matter is made up up of the neurons that have non-myelinated axons. The white matter is made up of neurons that have myleniated axons. The myelin sheath is white. The primary thinking, perceiving and cognitive functions of the brain happen on in the gray matter of the brain. The neurons in this part of the brain are short enough that the electrical signal would not degrade from the start of the cell body to the axon terminal, so no insulation or ion channel signal boosting is required.

In contrast, the axons and thus axonal tracts that go from the cerebral cortex to the inner brain structures and the spinal cord, are longer and need the insulation and signal boost. Thus where these neurons begin to predominate, the brain matter actually becomes white. As the surface of the brain is filled of many hills and valleys, the inner face between the gray matter and the white matter is irregular as well. The gray matter and white matter interface can be seen below.

The gray matter and white matter interface can be seen on this photograph of an autopsied human brain.

While in this photograph, the gray matter is more of a yellowish cream, the white matter is as a white as the name would imply. The boundaries where the gray matter and the white matter come together are known as the “gray matter/white matter interface.” In such areas, there is a significant difference in the density of brain material, which makes them considerably more vulnerable to stretching and shearing injuries when the brain is dynamically rotated within the skull.

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Gordon Johnson

Attorney Gordon Johnson is one of the nations leading brain injury advocates. He is Past-Chair of the TBILG, a national group of more than 150 brain injury advocates. He has spoken at numerous brain injury seminars and is the author of some of the most read brain injury web pages on the internet.

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Gray Matter and White Matter in the Brain