Types and Functions of Neurotransmitters
Neurotransmitter: a chemical messenger that allows nerve cells to communicate with each other. A neurotransmitter signal travels from a neuron, across the synapse, to the next neuron. The synapse is the name given to the space between the two neurons.
Neurotransmitters are synthesized in and released from nerve endings into the synaptic cleft. From there, neurotransmitters bind to receptor proteins in the cellular membrane of the target tissue. The target tissue gets excited, inhibited, or functionally modified in some other way.
Types and Functions of Neurotransmitters
There are a number of different ways to classify and categorize neurotransmitters. In some instances, they are simply divided into monoamines, amino acids, and peptides.
Neurotransmitters can also be categorized into one of six types:
- Gamma-aminobutyric acid (GABA): This naturally occurring amino acid acts as the body’s main inhibitory chemical messenger. GABA contributes to vision, motor control, and plays a role in the regulation of anxiety. GABA is located in many brain regions: hippocampus, thalamus, basal ganglia, hypothalamus, and brain steam.
- Its main functions are to regulate anxiety, vision, and motor control. People who do not have enough GABA may find they have poor impulse control and could lead to seizures in the brain.
- Lack of GABA may also result in mental health issues such as bipolar disorder and mania. If there is too much GABA, however, this could result in hypersomnia (oversleeping) and a lack of energy.
- Glutamate: The most plentiful neurotransmitter found in the nervous system, which supports cognitive functions such as memory formation and learning.
- Glutamate is an excitatory neurotransmitter, with receptors found in the central nervous system in the neurons and the glia. If there is an excess amount of glutamate, this could result in excitotoxicity – meaning that neurons are killed due to overactivations of glutamate receptors.
- If these neurons are destroyed, this could lead to conditions such as Alzheimer’s disease, stroke, and epilepsy.
- If there are not enough glutamate, this could result in psychosis, insomnia, concentration problems, mental exhaustion, or even death.
- Oxytocin: This powerful hormone acts as a neurotransmitter in the brain. It is produced by the hypothalamus and plays a role in social recognition, bonding, and sexual reproduction. Synthetic oxytocin such as Pitocin is often used as an aid in labor and delivery. Both oxytocin and Pitocin cause the uterus to contract during labor.
- Endorphins: This is an inhibitory type of neurotransmitter which works in lowering the transmission of pain signals to the brain and promotes feelings of euphoria. In terms of structure, endorphins are similar to opioids, and work in similar ways.
- Endorphins are primarily made within the hypothalamus and pituitary glands in response to pain but can also be released when completing physical activity (contributing to a ‘runner’s high’).
- There are not many known symptoms of having too many endorphins, but it could lead to an addiction to exercise. If there were a deficit in endorphins, this could result in feelings of depression, headaches, anxiety, mood swings, and a condition called fibromyalgia (chronic pain).
- Epinephrine: Also known as adrenaline, epinephrine is considered both a hormone and a neurotransmitter. Generally, epinephrine is a stress hormone that is released by the adrenal system. This is an excitatory class of neurotransmitters as it stimulates the central nervous system. If there is too much adrenaline in the bloodstream, this could lead to high blood pressure, anxiety, insomnia, and increased risk of a stroke. If there were too little adrenaline, however, this can lead to diminished excitement and not being able to react appropriately in stressful situations, diminishing the stress response.
- Norepinephrine: Also produced in the adrenal glands, this neurotransmitter is a naturally occurring chemical, also known as noradrenaline. This is an excitatory neurotransmitter as it stimulates the brain and body, also produced within the brainstem and hypothalamus.
- This chemical helps in activating the body and brain to take action during time of stress or when in dangerous situations.
- It is especially prevalent during the fight-or-flight response, aiding in alertness. Noradrenaline is at its peak during times of stress, but lowest during sleep cycles.
- If levels of noradrenaline are too high, this can lead to high blood pressure, excessive sweating, and anxiety. Low levels of this chemical could mean that energy levels are lower, concentration is lacking, and could also contribute to depressed feelings.
- Histamine: This organic compound acts as a neurotransmitter in the brain and spinal cord. It plays a role in allergic reactions and is produced as part of the immune system’s response to pathogens.
- Dopamine: Commonly known as the feel-good neurotransmitter, dopamine is involved in reward, motivation, and additions. Dopamine is both an excitatory and inhibitory neurotransmitter, as well as a neuromodulator. Several types of addictive drugs increase dopamine levels in the brain hence encouraging the individual to continue using these drugs to get that pleasure reward. A deficiency in dopamine could result in feelings of depression dopamine can also play a role in the coordination of body movements and a shortage can be seen in those with Parkinson’s disease – resulting in tremors and motor impairments.
- Serotonin: A hormone and neurotransmitter, serotonin plays an important role in regulating and modulating mood, sleep, anxiety, sexuality, and appetite. Selective serotonin reuptake inhibitors (SSRIs) are a type of antidepressant medication commonly prescribed to treat depression, anxiety, panic disorder, and panic attacks. SSRIs work to balance serotonin levels by blocking the reuptake of serotonin in the brain, which can help improve mood and reduce feelings of anxiety.
- Adenosine: This naturally occurring chemical acts as a neuromodulator in the brain and is involved in suppressing arousing and improving sleep. Adenosine is commonly found in the presynaptic regions of the hippocampus and acts as a central nervous system depressant.
- Consistently high levels of this neurotransmitter can cause hypersensitivity to touch and heat.
- If there is too little adenosine, this can cause anxiety and trouble sleeping. Caffeine is what is known as an adenosine blocker which causes the adenosine receptors to be blocked. This is why caffeine can cause issues with sleeping and is not recommended to drink too late in the day.
- Adenosine triphosphate (ATP): Considered to be the energy currency of life, ATP acts as a neurotransmitter in the central and peripheral nervous systems. It plays a role in autonomic control, sensory transduction, and communication with glial cells. Research suggests it may also have a part in some neurological problems including pain, trauma, and neurodegenerative disorders.
- Nitric oxide: This compound plays a role in affecting smooth muscles, relaxing them to allow blood vessels to dilate and increase blood flow to certain areas of the body.
- Carbon monoxide: This colourless, odourless gas can have toxic and potentially fatal effects when people are exposed to high levels of the substance. However, it is also produced naturally by the body where it acts as a neurotransmitter that helps modulate the body’s inflammatory response.
- Acetylcholine: Acetylcholine is the only known neurotransmitter of its kind, found in both the central nervous system and the parasympathetic nervous system. The main function of this type is focused on muscle movements, memory, and learning, associated with motor neurons.
Too much acetylcholine is linked with increased salivation, muscle weakening, blurred vision, and paralysis.
Too little acetylcholine is linked to learning and memory impairments, as well as being shown to have links to dementia and Alzheimer’s, according to research (Haam & Yakel, 2017; Tabet, 2006).