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In psychology, neurotransmitters are chemical messengers that facilitate communication between neurons in the brain and nervous system. They influence various psychological functions, including mood, emotion, stress response, and cognition.
Common neurotransmitters like serotonin and dopamine are often implicated in mental health disorders such as depression and anxiety. Their release, binding, and reuptake are essential for neural signaling and brain activity.Key Points
Common neurotransmitters like serotonin and dopamine are often implicated in mental health disorders such as depression and anxiety. Their release, binding, and reuptake are essential for neural signaling and brain activity.
Key Points
How Neurotransmitters Work
Forneuronsto send messages via neurotransmitters, they need to communicate with each other, which they do through synapses.
When signals travel through a neuron and reach the end of that neuron, they cannot simply travel through to the next one.
Instead, the neuron must trigger the release of neurotransmitters, which then carry signals across the synapses with the goal of reaching the next neuron.
During synaptic transmission, the action potential (an electrical impulse) triggers the synaptic vesicles of the pre-synaptic neuron to release neurotransmitters (a chemical message).
These neurotransmitters diffuse across the synaptic gap (the gap between the pre and post-synaptic neurons) and bind to specialized receptor sites on the post-synaptic neuron.
The neuron which releases the neurotransmitters is called the presynaptic neuron. The neuron which receives the neurotransmitters is called the postsynaptic neuron.
The end of each neuron has presynaptic endings and vesicles, which are sacks containing neurotransmitters.
Packets of serotonin molecules are released from the end of the presynaptic cell (the axon) into the space between the two nerve cells (the synapse).
After Neurotransmission
The neurotransmitters released from the presynaptic neuron may either excite or inhibit the postsynaptic neuron, telling it to either release neurotransmitters, slow down the release, or stop signaling completely.
After neurotransmission, the signal is terminated, allowing the neurons to return to a resting state.
When neurotransmitters get released into the synapse, not all are able to be attached to the receptors of the postsynaptic neuron. However, the gap between the neurons needs to be clearer of neurotransmitters at signal termination.
Classification
A neurotransmitter can influence neurons in one of three ways: it can excite, inhibit, or modulate them.
Whether a neurotransmitter is excitatory or inhibitory is dependent on the receptor it binds to on the postsynaptic neuron.
Some neurotransmitters can be both excitatory and inhibitory, depending on the context. Some can activate multiple receptors, as there is not just one receptor for each type of neurotransmitter.
1. Excitatory neurotransmitters
These types have an excitatory/stimulating effect on the neurons. If a neurotransmitter is excitatory, it will increase the likelihood that the neuron will fire action potential.
Examples of these types of neurotransmitters are epinephrine and norepinephrine.
2. Inhibitory neurotransmitters
In contrast to excitatory neurotransmitters, inhibitory neurotransmitters have the opposite effect, inhibiting/hindering the neurons.
If a neurotransmitter is inhibitory, it makes the likelihood of the neuron firing action potential will be decreased.
Examples of these types of neurotransmitters are GABA and endorphins.
3. Modulatory neurotransmitters
These are often called neuromodulators. If a neurotransmitter is a neuromodulate, this means it can affect a large number of neurons at the same time, as well as being able to influence the effects of other neurotransmitters.
Neuromodulators do not directly activate the receptors of neurons but work together with neurotransmitters to enhance the excitatory or inhibitory responses of the receptors.
Examples of these types of neurotransmitters are serotonin and dopamine.
Types
There are over 50 known types of neurotransmitters. Some of the main classifications are described below in a few categories: monoamines, amino acids, peptides, purines, and acetylcholine.
1. Monoamines
The monoamine group of neurotransmitters is especially important for psychologists as they are involved in a number of behaviors such as decision-making, emotional response, happiness, depression, andreward response.
Types of monoamines are serotonin, epinephrine, norepinephrine, and dopamine.
Serotoninplays a role as a neurotransmitter as well as a hormone. It is important in controlling mood and can affect the happiness levels of an individual.
Serotonin is also important for regulating anxiety, appetite, pain control, andsleep cycles. Serotonin is found in the enteric nervous system in the gastrointestinal tract (the gut) but is also produced in thecentral nervous systemin an area of the brain stem called the raphe nuclei.
Serotonin is of the inhibitory class of neurotransmitters as it does not stimulate the brain.
Instead, it balances out the excessive excitatory neurotransmitter effects. A deficit in serotonin can be linked todepression, sadness, fatigue, suicidal thoughts, and anxiety. It, therefore, plays a role in the underlying cause of many mental health issues.
EpinephrineThis neurotransmitter and hormone are also known as adrenaline. This is a stress hormone that is released into the bloodstream via the adrenal glands. This is an excitatory class of neurotransmitter 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 an increased risk of a stroke. If there is too little adrenaline, however, this can lead to diminished excitement and not being able to react appropriately in stressful situations, diminishing the stress response.
This neurotransmitter and hormone are also known as adrenaline. This is a stress hormone that is released into the bloodstream via the adrenal glands. This is an excitatory class of neurotransmitter 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 an increased risk of a stroke. If there is too little adrenaline, however, this can lead to diminished excitement and not being able to react appropriately in stressful situations, diminishing the stress response.
NorepinephrineAlso 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 times of stress or when in dangerous situations.It is especially prevalent during thefight-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.
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 times of stress or when in dangerous situations.
It is especially prevalent during thefight-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.
DopamineDopamineis produced in areas of the brain called the substantia nigra, ventral tegmental area, and the hypothalamus, projecting to the frontal cortex and thenucleus accubens(responsible for reward and pleasure) among other areas.Dopamine is both an excitatory and inhibitory neurotransmitter, as well as a neuromodulator, involved in reward, motivation, and addictions. A surplus of dopamine can result in competitive behaviors, aggression, poor control over impulses, gambling, and addiction.As such, addictive drugs can increase levels of dopamine, encouraging the individual to continue using these drugs to get that pleasure reward. A dopamine deficiency could result in feelings of depression.It is thought that 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.
Dopamineis produced in areas of the brain called the substantia nigra, ventral tegmental area, and the hypothalamus, projecting to the frontal cortex and thenucleus accubens(responsible for reward and pleasure) among other areas.Dopamine is both an excitatory and inhibitory neurotransmitter, as well as a neuromodulator, involved in reward, motivation, and addictions. A surplus of dopamine can result in competitive behaviors, aggression, poor control over impulses, gambling, and addiction.As such, addictive drugs can increase levels of dopamine, encouraging the individual to continue using these drugs to get that pleasure reward. A dopamine deficiency could result in feelings of depression.It is thought that 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.
Dopamineis produced in areas of the brain called the substantia nigra, ventral tegmental area, and the hypothalamus, projecting to the frontal cortex and thenucleus accubens(responsible for reward and pleasure) among other areas.
Dopamine is both an excitatory and inhibitory neurotransmitter, as well as a neuromodulator, involved in reward, motivation, and addictions. A surplus of dopamine can result in competitive behaviors, aggression, poor control over impulses, gambling, and addiction.
As such, addictive drugs can increase levels of dopamine, encouraging the individual to continue using these drugs to get that pleasure reward. A dopamine deficiency could result in feelings of depression.
It is thought that 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.
2. Amino Acids
Gamma-aminobutyric acid (GABA)GABA is a naturally occurring neurotransmitter that is known as the body’s primary inhibitory messenger. GABA is located in many brain regions:hippocampus,thalamus, basal ganglia, hypothalamus, and brain stem.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, which could lead to seizures in the brain.Lack of GABA may also result in mental health issues such as bipolar disorder andmania. If there is too much GABA, however, this could result in hypersomnia (oversleeping) and a lack of energy.
GABA is a naturally occurring neurotransmitter that is known as the body’s primary inhibitory messenger. GABA is located in many brain regions:hippocampus,thalamus, basal ganglia, hypothalamus, and brain stem.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, which could lead to seizures in the brain.Lack of GABA may also result in mental health issues such as bipolar disorder andmania. If there is too much GABA, however, this could result in hypersomnia (oversleeping) and a lack of energy.
GABA is a naturally occurring neurotransmitter that is known as the body’s primary inhibitory messenger. GABA is located in many brain regions:hippocampus,thalamus, basal ganglia, hypothalamus, and brain stem.
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, which could lead to seizures in the brain.
Lack of GABA may also result in mental health issues such as bipolar disorder andmania. If there is too much GABA, however, this could result in hypersomnia (oversleeping) and a lack of energy.
GlutamateAnother amino acid is glutamate, which supports cognitive functions such as memory formation and learning. This is known as the most abundant neurotransmitter, which is found in the central nervous system.Glutamate is an excitatory neurotransmitter with receptors found in the central nervous system in the neurons and theglia. 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 is not enough glutamate, this could result in psychosis, insomnia, concentration problems, mental exhaustion, or even death.
Another amino acid is glutamate, which supports cognitive functions such as memory formation and learning. This is known as the most abundant neurotransmitter, which is found in the central nervous system.Glutamate is an excitatory neurotransmitter with receptors found in the central nervous system in the neurons and theglia. 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 is not enough glutamate, this could result in psychosis, insomnia, concentration problems, mental exhaustion, or even death.
Another amino acid is glutamate, which supports cognitive functions such as memory formation and learning. This is known as the most abundant neurotransmitter, which is found in the central nervous system.
Glutamate is an excitatory neurotransmitter with receptors found in the central nervous system in the neurons and theglia. 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 is not enough glutamate, this could result in psychosis, insomnia, concentration problems, mental exhaustion, or even death.
3. Peptides
EndorphinsThis is an inhibitory type of neurotransmitter that 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).
This is an inhibitory type of neurotransmitter that 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).
This is an inhibitory type of neurotransmitter that 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).
4. Purines
AdenosineAdenosine is a neuromodulator type of neurotransmitter that functions in suppressing arousal and improving sleep cycles. Adenosine is commonly found in the presynaptic regions of the hippocampus and acts as acentral nervous systemdepressant.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 is a neuromodulator type of neurotransmitter that functions in suppressing arousal and improving sleep cycles. Adenosine is commonly found in the presynaptic regions of the hippocampus and acts as acentral nervous systemdepressant.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 is a neuromodulator type of neurotransmitter that functions in suppressing arousal and improving sleep cycles. Adenosine is commonly found in the presynaptic regions of the hippocampus and acts as acentral nervous systemdepressant.
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.
Another type of purine found in the central nervous system and theperipheral nervous system. ATP has a role in autonomic control, sensory transduction, and communication with glial cells.
5. Acetylcholine
Acetylcholine is the only known neurotransmitter of its kind found in both the central nervous system and theparasympathetic 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).
Disorders Associated with Neurotransmitters
Symptoms associated with mental health conditions such as mood and anxiety disorders andschizophreniaare believed to be the result in part of an imbalance of neurotransmitter levels in the brain.
Anxiety disorders may reflect the reduced GABA activity in the brain and an imbalance of its receptors. This has also been shown to be linked to an imbalance of serotonin and norepinephrine responses.
Similarly, there is also evidence that there may be links to increased excitability of glutamate in those with anxiety.
In depression, there is evidence of abnormalities in noradrenergic, dopaminergic, and serotonergic transmission.
Overall, serotonin has been shown to play a role inmood disordersas well as obsessive-compulsive disorder (OCD).
Finally, dopamine levels have been shown to be associated with addictions and schizophrenia. The sensitivity of dopamine receptors or too much dopamine is suggested to be associated with schizophrenia (Martin, Ressler, Binder, & Nemeroff, 2009).
The Effects of Drugs
Different types of drugs can affect the chemical transmission and change the effects of neurotransmitters. This can include medications used to alleviate the symptoms of certain mental health conditions, such as SSRIs, benzodiazepines, and anti-psychotics.
Medication
Illicit Drugs
Depending on the type, illicit drugs can either slow down or speed up the central nervous system and autonomic functions. Marijuana contains the psychoactive chemical tetrahydrocannabinol (THC), which interacts with and binds to cannabinoid receptors. This produces a relaxing effect and can also increase levels of dopamine.
Heroin binds to the opioid receptors and triggers the release of extremely high levels of dopamine. The more that heroin is used, the more likely a tolerance will develop from it, meaning that the brain will not function the way it did before starting the drug.
This can cause levels of dopamine to drop when the drug is stopped, which can ultimately lead to this drug being addictive so the user can feel the ‘high’ from the dopamine again.
Cocaine is a stimulant drug as it speeds up the central nervous system, increasing heart rate, blood pressure, alertness, and energy. Cocaine essentially gives the brain a surge of dopamine with quick effects. The effects of cocaine do not typically last very long and can make a person irritable or depressed afterward, leading to a craving for more.
Ecstasy can bring about feelings of pleasure and warmth, overall decreasing anxiety in the moment. However, regular use and aftereffects can increase anxiety, irritability, sleep difficulties, and depressed feelings.
References
Boto, T., & Tomchik, S. M. (2019). The excitatory, the inhibitory, and the modulatory: mapping chemical neurotransmission in the brain.Neuron, 101(5), 763-765.
Martin, E. I., Ressler, K. J., Binder, E., & Nemeroff, C. B. (2009). The neurobiology of anxiety disorders: brain imaging, genetics, and psychoneuroendocrinology.The Psychiatric Clinics of North America, 32(3), 549–575. https://doi.org/10.1016/j.psc.2009.05.004.
Haam, J., & Yakel, J. L. (2017). Cholinergic modulation of the hippocampal region and memory function.Journal of Neurochemistry, 142, 111-121.
Tabet, N. (2006). Acetylcholinesterase inhibitors for Alzheimer’s disease: anti-inflammatories in acetylcholine clothing!.Age and Ageing, 35(4), 336-338..
Watkins M. (2020, February 3).How Drugs Affect the Brain and Central Nervous System. American Addiction Centers. https://americanaddictioncenters.org/health-complications-addiction/central-nervous-system .
Further InformationNicholls, J. G., Martin, A. R., Wallace, B. G., & Fuchs, P. A. (2001). From neuron to brain (Vol. 271). Sunderland, MA: Sinauer Associates.Pereda, A. E. (2014). Electrical synapses and their functional interactions with chemical synapses. Nature Reviews Neuroscience, 15(4), 250-263.
Further Information
Nicholls, J. G., Martin, A. R., Wallace, B. G., & Fuchs, P. A. (2001). From neuron to brain (Vol. 271). Sunderland, MA: Sinauer Associates.Pereda, A. E. (2014). Electrical synapses and their functional interactions with chemical synapses. Nature Reviews Neuroscience, 15(4), 250-263.
Saul McLeod, PhD
BSc (Hons) Psychology, MRes, PhD, University of Manchester
Saul McLeod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.
Olivia Guy-Evans, MSc
BSc (Hons) Psychology, MSc Psychology of Education
Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.
