What Are Neurotransmitters?

Neurotransmitters are chemical messengers in the body. They are used by the nervous system to help neurons, or nerve cells, communicate with one another. They also help neurons transmit signals to other target cells throughout the body.

How They Work

Neurons work as a sort of messaging system. They have electrical signals that get passed along their axon, which is a thin cable that connects the main part of the cell to other neurons. Once the electrical signal reaches the synapse, a tiny gap at the end of the axon, it is then converted into a chemical signal.

This chemical signal is released from the neuron in a vesicle, or sac, through the synapse, becoming a neurotransmitter and transporting the signal to the receiving neuron. This prompts the receiver to respond in a specific way so that it can interpret the message being sent.

Receptors are designed to regulate the release of a neurotransmitter or receive the signal being sent. Receptors are located between neurons and allow for the exchange of information to occur. This process is known as neurotransmission.

When They’ve Done Their Job

Once a neurotransmitter has completed its task, it is no longer needed. There are three ways that communication with the neurotransmitter can be stopped.

The first is through a process called degradation. This process occurs when an enzyme comes in and changes the composition of the neurotransmitter. When this happens, the receptor no longer recognizes the neurotransmitter and therefore does not interact with it.

The second process is known as diffusion, when the neurotransmitter moves away from the receptor. The third is the reuptake process, which occurs when the neuron that released the neurotransmitter collects it and takes it back up its axon.  

Types

There are over 100 types of neurotransmitters, but it can be hard to determine whether something counts as a neurotransmitter or not. This is because it’s not easy to see what type of chemical is within the sacs that are released from neurons.

There are some specific guidelines that researchers use to help figure out which molecules are neurotransmitters. For one, the cell must contain a chemical that is released in a standard or appropriate amount when it is stimulated in a certain way.

The chemical also must be released by a specific neuron that is presynaptic and then binds properly to receptors on a postsynaptic neuron. After the neurons have sent and received the message, the neurotransmitter itself must go through one of the removal processes.

Out of all the neurotransmitters, some stand out more than others because they are better known or because they are found in a greater amount. For example, some neurotransmitters are the focus in clinical settings for a variety of diseases. These neurotransmitters include:

• Acetylcholine: This neurotransmitter stimulates muscles to contract and plays an important role in various cognitive functions, such as memory. It is also associated with Alzheimer’s disease.
• Dopamine: This is known as a feel-good chemical and plays a role in Parkinson’s disease.
• Glutamate: It is the most abundant amino acid in the brain and can lead to cell death because of its ability to elicit a toxic response in cells.
• GABA (gamma-aminobutyric acid): This is an amino acid that acts as a neurotransmitter in the brain and can act as a stress reducer, too.
• Serotonin: It is a well-known neurotransmitter that is found in abundance in the digestive system. It is typically associated with depression.

These neurotransmitters fall into the category of how they cause the receptor to react, which are:

• Excitatory: When the neurotransmitter provokes this response, the receiving neuron generates a new electrical signal known as an action potential, or a nerve impulse. It is designed to transmit a certain message or elicit an action from other cells. For example, if you touch something hot, neurotransmission will occur and alert you to the sensation of heat via an excitatory response. Glutamate is an excitatory neurotransmitter.
• Inhibitory: This response helps stop a specific response from other cells in the body. It prevents an excitatory response. GABA is an inhibitory neurotransmitter.
• Modulatory: Modulatory responses can regulate more than just one neuron after neurotransmission, meaning they can send the same message to various neurons at the same time. They operate more slowly than the other responses. Dopamine and serotonin are modulatory neurotransmitters.

Acetylcholine

This type of neurotransmitter is abundant in the central nervous system and the peripheral nervous system. It acts as a neuromodulator because it can send signals to many receptors at the same time. It plays a vital role in cognition, learning, attention, and memory.

Acetylcholine can also elicit other types of feelings or emotions, such as motivation and arousal. It also plays a major role in voluntary muscle movement. That means that when you tell your body to get up and walk around, acetylcholine is a part of that signaling process.   

Amino Acids

Amino acids are essential for neurotransmission. This is because many amino acids act as neurotransmitters. Some other amino acids also play a role in the production of certain neurotransmitters. They can modulate neurotransmission and ensure that the body has enough of the essential neurotransmitters that are needed for proper physical and mental health.

For example, serotonin, which helps regulate mood, relies heavily on the amino acid tryptophan. Without tryptophan, serotonin levels may drop, and this can lead to depression.

Gasotransmitters

Gasotransmitters are neurotransmitters that are formed out of small molecules of gas. The three gasotransmitters include nitric oxide, hydrogen sulfide, and carbon monoxide. They are involved in signaling processes and play a vital role in synaptic plasticity, or the synapse's ability to get weaker or stronger over time.

In synapses that become weaker, gasotransmitters also help restore their plasticity. Research shows that positive or negative changes in the gasotransmitters can lead to psychiatric conditions.

Monoamines

Some neurotransmitters are monoamines, which are compounds that have only one amine group in the molecule. Examples of neurotransmitters that fall into this category include dopamine, norepinephrine, epinephrine, and serotonin. They can play a role in the development of neurological syndromes.   

Peptides

Some peptides, or hormones, can act as neurotransmitters. The way peptides act depends on the amino acid sequence they possess. Peptides that can act as neurotransmitters are often called neuropeptides, and they act more slowly than typical neurotransmitters. This means that they can produce a response that leads to a longer action than neurotransmitters. Some examples of neuropeptides include B-endorphin and oxytocin.  

Purines

Purines are organic compounds that can be found in the body and some foods. They are formed when DNA breaks down, turning into uric acid in the blood.

When purines act as neurotransmitters, they play a role in several system responses in the body. Adenosine triphosphate (ATP) is a purine that acts as a neurotransmitter in both the central and peripheral nervous systems. ATP plays a role in the signaling between glial cells, which maintain balance in the body.

Problems

Neurotransmitters are vital to the health of the body and mind. Low levels of any type of neurotransmitter can lead to the development of different diseases. Too many neurotransmitters can also pose the same risks. For example, if there are too few dopamine neurotransmitters in the brain, it could lead to the development of Alzheimer’s disease.

An increased level of neurotransmitters that send pain signals and a decrease in the levels of neurotransmitters that inhibit pain signals have been associated with fibromyalgia, a condition characterized by widespread pain. This imbalance in inhibitory and excitatory neurotransmitters is thought to play a role in the development and progression of this disease.

Having too much serotonin in the body could be life-threatening and lead to a condition known as serotonin syndrome. The symptoms of serotonin syndrome can include:

• Agitation
• Anxiety
• Restlessness
• Tremors
• Muscle rigidity
• High blood pressure
• Hyperthermia (high body temperature)
• Flushed skin
• Overexcitement
• Fast heart rate
• Involuntary muscle contractions
• Fast breathing

In other cases, receptors can become sensitive to neurotransmitters. When this happens, less of a neurotransmitter can elicit a greater response. It can occur in people taking medications that interact with specific neurotransmitter receptors such as antidepressants.

Summary

Neurotransmitters are chemical messengers that help nerve cells communicate with each other. They include serotonin, dopamine, glutamate, and acetylcholine. Neurotransmitters serve several functions, such as regulating appetite, the sleep-wake cycle, and mood. Low levels of any neurotransmitter can lead to problems, including fibromyalgia and Alzheimer's disease.