A neuron has three main parts. The cell body directs all activities of the neuron. Dendrites extend out from the cell body and receive messages from other nerve cells. An axon is a long single fiber that transmits messages from the cell body to the dendrites of other neurons or to other body tissues, such as muscles. A protective covering called the myelin sheath, covers most neurons. Myelin insulates the axon and helps nerve signals travel faster and farther.