The approximately 100 billion cells in the human brain fall into two broad classes: neurons and glial cells. Neurons are responsible for sensory, cognitive and motor functions, while glial cells provide structural and metabolic support.
Brain cells are composed of the same molecules, and many of the same proteins, as the other cells of the body, though some cells are specialized to their role in the brain. Neurons, for example, have three distinct components. The soma, or cell body, is similar to the bodies of other cells and has a nucleus, organelles and plasma membrane. A long filament, which is called an axon terminal, extends from the neuron's soma and carries messages for the cell. Messages are transmitted at the end of the terminal via small tendrils called dendrites. Dendrites are separated from other neurons by a short gap called a synapse.
Glial cells are distinct from neurons and are shaped like sea urchins with a small central body and multiple tendrils extending outward. These cells surround neurons and preserve their relative positions. They act to insulate neurons from each other to prevent signal leaks and provide nutritional support for the glucose-hungry neurons. Glial cells also destroy pathogens and clear away cellular debris that has accumulated in the brain.