Your nervous system contains millions of nerve cells, called neurons. Neurons are highly specialised to transmit messages from one part of your body to another.
All neurons have a cell body and one or more fibres. These fibres vary in length from microscopic to over 1 metre. There are two different kinds of nerve fibres: fibres that carry information towards the cell body, called dendrites, and fibres that carry information away from it, called axons. Nerves are tight bundles of nerve fibres.
Your neurons carry messages in the form of electrical signals called nerve impulses. To create a nerve impulse, your neurons have to be excited. Stimuli such as light, sound or pressure all excite your neurons, but in most cases, chemicals released by other neurons will trigger a nerve impulse.
Although you have millions of neurons that are densely packed within your nervous system, they never actually touch. So when a nerve impulse reaches the end of one neuron, a neurotransmitter chemical is released. It diffuses from this neuron across a junction and excites the next neuron.