When two nerve cells need to communicate, they can’t just tap each other on the shoulder. These neurons pass information from one end of their “body” to the other as a tiny electrical signal. But one cell doesn’t actually touch another, and the signals can’t jump across the tiny spaces in between. To cross those tiny gaps, called synapses, they rely on chemical messengers. These chemicals are known as neurotransmitters. And their role in cell talk is called neurotransmission.
When an electrical signal reaches the end of a neuron, it triggers the release of tiny sacs that had been inside the cells. Called vesicles, the sacs hold chemical messengers such as dopamine (DOAP-uh-meen) or serotonin (Sair-uh-TOE-nin).
As it moves through a nerve cell, an electrical signal will stimulate these sacs. Then, the vesicles move to — and merge with — their cell’s outer membrane. From there, they spill their chemicals into the synapse.
Those freed neurotransmitters then float across the gap and over to a neighboring cell. That new cell has receptors pointing toward the synapse. These receptors contain pockets, where the neurotransmitter needs to fit.
A neurotransmitter docks into the proper receptor like a key into a lock. And as a messenger chemical moves in, the receptor’s shape will change. This change can open a channel in the cell, allowing charged particles to enter or exit. The shape change can trigger other actions inside the cell as well.
If the chemical messenger binds to a certain type of receptor, electrical signals will flow down the length of its cell. This moves the signal along the neuron. But neurotransmitters also can bind to receptors that will block an electrical signal. That will stop a message, silencing it.
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Signals for all of our sensations — including touch, sight and hearing — are relayed this way. So are the nerve signals that control movements, thoughts and emotions.
Each cell-to-cell relay in the brain takes less than a millionth of a second. And that relay will repeat for as far as a message needs to travel. But not all cells chat at the same speed. Some are relatively slow talkers. For instance, the slowest nerve cells (those in the heart that help regulate its beating) travel at about one meter (3.3 feet) per second. The fastest — cells that sense your muscles’ position as you walk, run, type or do backflips — race along at around 100 meters per second! Give someone a high five, and the brain — about a meter away — will get the message just one-hundredth of a second later.