Nerve anatomy. Artwork showing the anatomy and structure of a nerve cell (neuron, upper left) and the nerve process (axon) connecting it to other nerve cells. The axon is covered in an insulating material called myelin (green), and ends in branching terminal points (lower right). This insulation allows electrical impulses to pass from one nerve cell to the next, using chemical transmitters to cross the synaptic gap between cells at the terminal points shown here. Also shown are shorter processes called dendrites (purple). There are billions of neurons in a human brain.