A neurotransmitter is defined as a chemical messenger that carries, boosts, and balances signals between neurons, or nerve cells, and other cells in the body. These chemical messengers can affect a wide variety of both physical and psychological functions including heart rate, sleep, appetite, mood, and fear. Billions of neurotransmitter molecules work constantly to keep our brains functioning, managing everything from our breathing to our heartbeat to our learning and concentration levels.
How Neurotransmitters Work
In order for neurons to send messages throughout the body, they need to be able to communicate with one another to transmit signals. However, neurons are not simply connected to one another. At the end of each neuron is a tiny gap called a synapse and in order to communicate with the next cell, the signal needs to be able to cross this small space. This occurs through a process known as neurotransmission.In most cases, a neurotransmitter is released from what’s known as the axon terminal after an action potential has reached the synapse, a place where neurons can transmit signals to each other.
When an electrical signal reaches the end of a neuron, it triggers the release of small sacs called vesicles that contain the neurotransmitters. These sacs spill their contents into the synapse, where the neurotransmitters then move across the gap toward the neighboring cells. These cells contain receptors where the neurotransmitters can bind and trigger changes in the cells.After release, the neurotransmitter crosses the synaptic gap and attaches to the receptor site on the other neuron, either exciting or inhibiting the receiving neuron depending on what the neurotransmitter is. The neurotransmitters act like a key and the receptor site act like a lock. It takes the right key to open specific locks. If the neurotransmitter is able to work on the receptor site, it triggers changes in the receiving cell.
Sometimes neurotransmitters can bind to receptors and cause an electrical signal to be transmitted down the cell (excitatory). In other cases, the neurotransmitter can actually block the signal from continuing, preventing the message from being carried on (inhibitory).So what happens to a neurotransmitter after its job is complete? Once the neurotransmitter has had the designed effect, its activity can be stopped by different mechanisms.
- It can be degraded or deactivated by enzymes
- It can drift away from the receptor
- It can be taken back up by the axon of the neuron that released it in a process known as reuptake
Neurotransmitters can be classified by their function:
Excitatory neurotransmitters: These types of neurotransmitters have excitatory effects on the neuron, meaning they increase the likelihood that the neuron will fire an action potential. Some of the major excitatory neurotransmitters include epinephrine and norepinephrine.
Inhibitory neurotransmitters: These types of neurotransmitters have inhibitory effects on the neuron; they decrease the likelihood that the neuron will fire an action potential. Some of the major inhibitory neurotransmitters include serotonin and gamma-aminobutyric acid (GABA).
Some neurotransmitters, such as acetylcholine and dopamine, can create both excitatory and inhibitory effects depending upon the type of receptors that are present.
Modulatory neurotransmitters: These neurotransmitters, often referred to as neuromodulators, are capable of affecting a larger number of neurons at the same time. These neuromodulators also influence the effects of other chemical messengers. Where synaptic neurotransmitters are released by axon terminals to have a fast-acting impact on other receptor neurons, neuromodulators diffuse across a larger area and are more slow-acting.