Nerves are responsible for carrying messages around the body in the form of electrical impulses. The nerve cell can be stimulated by various impulses. For example, the photoreceptors in the eye's retina are stimulated by light, whereas touch receptors in the skin are stimulated by pressure.

The stimulus produces an electrical impulse in the nerve cell. This impulse travels along the nerve cell at a speed of more than 100 meters per second. When an impulse arrives at the axon terminal, a neurotransmitter is released. The neurotransmitter chemically transfers the stimulus to the neighbouring neuron.

Synapses are usually formed between axon terminals of the sending neuron and the dendrites of the receiving neuron. Inside the axon terminal of the sending cell, many synaptic vesicles filled with neurotransmitter molecules can be found. There is a small gap between the axon terminal of the sending neuron and the membrane of the receiving cell. This gap is called the synaptic cleft. When an electrical impulse arrives, a neurotransmitter is released into the synaptic cleft.

Many painkillers and anaesthetics prevent the transmission of nerve impulses across synapses. In other words, a stimulus that produces pain is created, but the information about it does not reach the brain and we do not feel pain.