How do nerves connect with each other?
The electrical signals (nerve impulses) carried by neurons are passed on to other neurons at junctions called synapses. The signal may be directly transferred at electrical synapses or, if there is no physical link between adjacent neurons, the signal is carried across the gap by chemicals called neurotransmitters. By using neurotransmitters, the nervous system can alter the way a message is passed on. Each neuron communicates with many others and this contributes to the amazing complexity of the brain.
What is a synapse?
When a nerve impulse reaches the synapse at the end of a neuron, it cannot pass directly to the next one. Instead, it triggers the neuron to release a chemical neurotransmitter. The neurotransmitter drifts across the gap between the two neurons. On reaching the other side, it fits into a tailor-made receptor on the surface of the target neuron, like a key in a lock. This docking process converts the chemical signal back into an electrical nerve impulse.
Why use neurotransmitters?
Your brain uses over 50 different neurotransmitter chemicals. Although electrical signalling between neurons is quicker and more energy efficient, chemical signalling is far more versatile. The signals carried by some neurotransmitters excite the target cell while others dampen down their activity, depending on the type of neurotransmitter released at the synapse and the receptors they reach. This is what sharpens the contrast between light and dark in the eye, for example.