Nerve impulses travel directly across connected synapses via electricity, while the impulses use special chemicals to cross non-touching synapses, according to the Science Museum of the South Kensington Museum in London. These chemicals are called neurotransmitters, and they can change the way nerves communicate with each other in the brain. The neuron that sends the message is usually called the presynaptic neuron, while the receiving neuron is called the postsynaptic neuron.
The Science Museum website explains that impulses that reach a synapse located at the end of a nerve cell, which necessitates that the impulse must travel across a gap, stimulate the neuron to produce and secrete a neurotransmitter. This neurotransmitter drifts across the gap, eventually contacting the postsynaptic neuron. When the neurotransmitter reaches the post-synaptic neuron, it converts the energy held in its chemical bonds into an electrical impulse. This impulse then continues down the post-synaptic neuron to its target. The postsynaptic neuron features a gap that only accommodates the correct neurotransmitter, eliminating the chance that it is stimulated inadvertently by the wrong neurotransmitter.
The body uses more than 50 neurotransmitters, according to the Science Museum. While electrical impulses are a quicker way to send and receive signals, neurotransmitters provide greater flexibility. For instance, neurotransmitters are better able to send more complex signals. Such abilities allow the human eye to distinguish between light and dark.