National Institute on Drug Abuse
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.
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cell The smallest structural and functional unit of an organism. Typically too small to see with the naked eye, it consists of watery fluid surrounded by a membrane or wall. Animals are made of anywhere from thousands to trillions of cells, depending on their size. Some organisms, such as yeasts, molds, bacteria and some algae, are composed of only one cell.
cell membrane Separates the inside of a cell from the outside of it. Some particles are permitted to pass through the membrane.
chemical A substance formed from two or more atoms that unite (become bonded together) in a fixed proportion and structure. For example, water is a chemical made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O. Chemical can also be an adjective that describes properties of materials that are the result of various reactions between different compounds.
control A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that give scientists something against which they can compare their experimental data.
docking The act of bringing together and inserting one thing into another.
dopamine A neurotransmitter, this chemical helps transmit signals in the brain.
membrane A barrier which blocks the passage (or flow through of) some materials depending on their size or other features. Membranes are an integral part of filtration systems. Many serve that same function as the outer covering of cells or organs of a body.
molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
neuron The impulse-conducting cells that make up the brain, spinal column and nervous system.
neurotransmitter A chemical released at the end of a neuron to carry a message to a neighboring cell. This chemical travels across the space between two cells, and then binds to molecules on a neighboring cell to transmit a message. Neurotransmitters are released from neurons, and can bind to neurons or to other types of cell, including those that make up muscles or glands.
receptor (in biology) A molecule in cells that serves as a docking station for another molecule. That second molecule can turn on some special activity by the cell.
serotonin A chemical present in blood that constricts blood vessels and communicates signals in the brain and nervous system.
synapse The junction between neurons that transmits chemical and electrical signals.
vesicles Small fluid-filled sacs inside cells. These sacs can hold chemicals that can be released either within the cell or outside of it.