What is the difference between grey and white matter in the brain?

Grey matter is greyish in colour because of the grey nuclei of cells and fills 40% of the brain, but consumes 94% of the oxygen.

White matter is whitish in colour because of myelin and fills 60% of the brain.

White matter is made up of long extending nerve fibers (axons) and connects various grey matter areas.

Grey matter is made up of neurons, dendrites, glial cells, synapses, and capillaries which are involved in muscle control, sensory perception, memory, emotions, speech, and self-control.

Grey matter contols how brain processing and cognition.

White matter controls how the brain functions and also controls temperature, blood pressure, heart rate.

Smokers loose grey matter at a greater rate than non-smokers.

The elderly with more grey matter have better cognitive function.

A US study has shown that there is an association in children between poverty and lower volume of grey matter.

Damage to white matter may be a sign of Alzheimers, even though Alzheimers is a grey matter disease.

Alcohol use may decrease white matter volume.

What is a synapse?

A synapse is a very small gap between two nerve cells (neuron). An electrical or chemical impulse triggers neurotransmitters to carry information across the synapse.

The word synapse is from two Greek words, "syn" and "haptein" meaning "together" and "to clasp" respectively.

When the connection between two neurons is strengthened, this results in the storage of information, which becomes memory.

Why is fat bad for the brain?

A high fat diet produces inflammation in the body, including in the brain.

Inflammation stimulates the microglia, which are part of the brains' immune system, and whose function is to destroy infection, by moving (staying active).

In obesity, these cells stop moving but eat brain synapses instead of the infectious bodies they are meant to destroy.  Functioning synapses are needed for learning which is a very important brain function.

On a mouse study, it was found that the effects of a high fat diet can be reversed in two weeks.