A neuron is a brain cell, the basic building block of the brain. The entire brain is actually a huge network of interlocking, interacting neurons.

There are about one hundred billion neurons in the human brain and several times that amount of glial and other smaller cells that support neuronal function.

A neuron is composed of a(n):

1. Cell Body
2. Axon
3. Dendrites
   

The contact point between the dendrite of one cell and the axon terminal of another is called the synapse. Neurons communicate across synapses with chemical messengers known as neurotransitters.

The neuron sending the message is called the pre-synaptic neuron while the neuron receiving the message is the post-synaptic neuron. The gap between the neurons is called the synaptic cleft.

Axons are coated by a fatty sheath known as myelin that speeds up the rate that the action potential travels down the axon. Because myelinated axons are white in appearance, brain tissue made up of these fibers is called white matter.

In contrast, grey matter refers to brain tissue made up of dendrites and cell bodies (as well as glial cells and capillaries). The surface of the cortex is composed of grey matter.