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Neurotransmitters are chemical messengers that send signals from neurones to receiving cells.
These cells could be another neurone, a gland, or muscle. There is a synaptic cleft between each neurone, a little space where neurotransmitters pass from one neurone to another. The synaptic cleft is where many important processes occur and where neurotransmitters ‘work’.
Neurotransmitters are the chemical messengers sent by presynaptic neurones (the cell that sends the signals) to postsynaptic neurones (the cell that receives the signals) through the small space between them (the synaptic cleft). This process occurs when an action potential is generated and transmitted to the synapse. This, then, triggers the release of neurotransmitters from the axon terminal (the ends of the axons).
For a neurotransmitter to reach the synaptic cleft, it travels in small synaptic vesicles (tiny bubble-like structures containing the neurotransmitters) from the presynaptic neurone. These synaptic vesicles then release the neurotransmitters into the synaptic cleft, where they will find binding sites (receptors) on the receiving cell.
A neurotransmitter’s function and effect on the receiving cell (postsynaptic neurone) varies depending on the receptor they have to receive the neurotransmitter.
This process is what happens when one neurone communicates with another. As neurones don’t connect, an electrical signal from one neurone is transmitted to another. What happens essentially is that each neurone triggers an electrical impulse in the next neurone.
There are a lot of keywords here that can be confusing. An excellent way to remember them is to prioritise learning the main ones. The prefixes (pre- and post-) indicate the direction of where the neurotransmitter is going.
For instance, a neurotransmitter travels from the PREsynaptic neurone, through the synaptic cleft, to the POSTsynaptic neurone. The synaptic cleft is the little space between the presynaptic and the postsynaptic neurone.
Overall, synaptic transmission is where an action potential (a term we covered in our Process of Synaptic Transmission article) starts the presynaptic neurone by preparing the synaptic vesicles with the neurotransmitter inside.
As we said before, the receptor has a role in how a neurotransmitter affects the postsynaptic neurone. In the same way, different types of neurotransmitters also impact the postsynaptic neurone.
When a neurotransmitter is released into the synaptic cleft, it creates a reaction.
We can divide neurotransmitters into two main classifications. It essentially boils down to whether or not the neurotransmitter will cause an action potential in the postsynaptic neurone.
Excitatory | Inhibitory |
These neurotransmitters increase the likelihood of a resulting action potential occurring in the postsynaptic neurone or receiving cell. | These neurotransmitters decrease the likelihood of a resulting action potential occurring in the postsynaptic neurone or receiving cell. |
The neurotransmitter will cause an action potential by affecting and influencing the ion flow across cell membranes of the neurones to cause an excitatory or inhibitory effect. Neurotransmitters can also act as modulators: they can significantly impact many neurons and other neurotransmitters simultaneously. They often work with other neurotransmitters to enhance the impact of excitation or inhibition.
Here are some examples of excitatory neurotransmitters:
Here are some examples of inhibitory neurotransmitters:
Serotonin and dopamine are also examples of neuromodulators.
When we consider the effects of neurotransmitters such as serotonin, GABA, and epinephrine on the body, we can say that neurotransmitters significantly impact behaviours. Serotonin may make a person more calm and relaxed, whilst epinephrine (adrenaline), an essential factor in the fight-or-flight response, can have the complete opposite effect on behaviour. A person will feel more alert and anxious and experience feelings of fear with epinephrine.
Similarly, dopamine significantly affects behaviours, primarily when these behaviours result in dopamine release.
The ventral tegmental area (VTA) is one of the major areas associated with dopamine within the brain, as it has a lot of dopaminergic neurones. It is connected to the substantial nigra, another hotspot of the dopaminergic areas in the brain.
The VTA is very heavily associated with feelings of rewards and motivation. As a result, it is closely linked to drug abuse and addiction.
The drug cocaine has an inhibitory effect on dopamine transporters within these two dopaminergic areas: it inhibits dopamine reuptake in the VTA. Thus, dopamine in these dopaminergic areas remains in the synapses for longer, extending the rewarding feelings. This is what causes that infamous feeling of euphoria when people take cocaine. Cocaine is essentially just prolonging the effects of dopamine in the brain’s reward pathways.
Addiction becomes a problem when it takes more quantities of cocaine to produce the same effect.
Neurotransmitters differ in categorising, but we can typically separate them into three major types: amino acids, monoamines, and peptides.
There are further categories to organise neurotransmitters. There are up to six categories overall. They are known as gasotransmitters, purines, and trace amines. Acetylcholine has its class!
Neurotransmitters that are classified within the amino acid type are:
Glutamate.
GABA.
Neurotransmitters that are classified within the monoamine type are:
Epinephrine.
Dopamine.
Serotonin.
Neurotransmitters that are classified within the peptide type are:
Here is a chart indicating the biosynthetic precursor(s) of neurotransmitters. It shows you how some of the neurotransmitters are made up:
Neurotransmitter biosynthetic precursor chart
When things are going right with neurotransmitters, you can navigate your daily life without much hindrance. Your brain can operate and react accordingly to different situations.
However, certain disorders can occur when there is an imbalance in neurotransmitters:
Medications for these disorders often affect the neurotransmitter associated with them. For instance, schizophrenic patients often have antipsychotic medications that influence their dopamine levels. They work by blocking dopamine receptors in the brain, preventing dopamine uptake.
Those with depression often use drugs that increase serotonin levels by preventing the reuptake of serotonin. Thus, serotonin remains in the synapses for longer.
We often refer to drugs affecting neurotransmitters as agonists or antagonists:
Agonists work by aiding the uptake of neurotransmitters at the receptors on the postsynaptic neurone/receiving cell. They bind to the synaptic receptors and facilitate the effects of the neurotransmitter.
Antagonists work by binding to synaptic receptors as well. However, they reduce the effects of a neurotransmitter.
Do not confuse this with excitatory and inhibitory effects. Agonists will aid the effect of the neurotransmitter, both if it’s excitatory or inhibitory. It applies to antagonists, too, as antagonist drugs will reduce the excitatory or inhibitory effect.
Neurotransmitters are chemical messengers that transmit signals between neurones to receiving cells. These could be another neurone, a gland, or muscle.
They do so in different ways, depending on the neurotransmitter. Some will make a person behave calmly and more relaxed, whilst others cause feelings of anxiety to behave more erratically. For instance, dopamine gives you a sense of motivation and is a significant part of the reward pathways in the brain. If you do something that activates this, it will provide you with a 'good feeling', making you more inclined to repeat the behaviour.
Key neurotransmitters of interest in psychology include serotonin, dopamine, glutamate, and GABA.
Neurotransmitters work by allowing presynaptic neurones to communicate with receiving cells (the postsynaptic neurones) through the small space between them (the synaptic cleft).
Typically, this occurs when an action potential is generated and transmitted to the synapse, which triggers the release of neurotransmitters from the axon terminal (the ends of the axons). Neurotransmitters then bind to the receptors and either inhibit or excite the postsynaptic neurone, stopping or continuing the action potential.
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