VonOlivia Guy-Evans, released April 20, 2021
vonSaul Mcleod, PhD
- Neurons do not have direct contact. There is a very small gap between neurons called a synapse. The signal must cross this gap to continue its journey to or from the CNS. It does this with chemicals diffusing through the gap between the two neurons. These chemicals are called neurotransmitters.
- Neurotransmitters are chemical messengers released by neurons from a synaptic vesicle into the synapse.
- Some neurotransmitters work by charging the neuron more negatively, making it less likely to fire. This is an inhibitory effect. This is the case forSerotonin. Inhibitory neurotransmitters are generally responsible for quieting the mind and inducing sleep.
- Other neurotransmitters increase the positive charge, making the neuron more likely to fire. This is the arousing effect. Adrenaline is both a neurotransmitter and an excitatory hormone.
A neurotransmitter is a chemical messenger that enables nerve cells to communicate with each other. A neurotransmitter signal travels from aNeuron,across the synapse, to the next neuron. The space between the two neurons is called the synapse.
Neurotransmitters are important in amplifying and balancing signals in the brain and maintaining brain function. They help control automatic responses like breathing and heart rate, but they also have psychological functions like learning, mood control,fear, Happiness and luck.
How neurotransmitters work
In order for neurons to send messages via neurotransmitters, they must communicate with each other, which they do via synapses.
When signals travel through a neuron and reach the end of that neuron, they can't just pass through to the next. 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 presynaptic neuron to release neurotransmitters (a chemical message).
These neurotransmitters diffuse across the synaptic gap (the gap between the pre- and postsynaptic neurons) and bind to specialized receptor sites on the postsynaptic neuron.
The neuron that releases the neurotransmitters is called the presynaptic neuron. The neuron that receives the neurotransmitters is called the postsynaptic neuron.
The end of each neuron has presynaptic terminals and vesicles, which are sacs that contain neurotransmitters.
When a nerve impulse (or action potential) triggers the release of neurotransmitters, those chemicals are then released into the synapse and then picked up by the next neuron's receptors. This process is called neurotransmission.
Packets of serotonin molecules are released from the end of the presynaptic cell (the axon) into the space between the two neurons (the synapse). These molecules can then be taken up by receptors on the postsynaptic nerve cell (the dendrite) and thus pass on their chemical message. Excess molecules are taken up again by the presynaptic cell and processed further.
The neurotransmitters released by the presynaptic neuron can either excite or inhibit the postsynaptic neuron, telling it to either release neurotransmitters, slow the release, or stop signaling entirely.
After neurotransmission, the signal is terminated, allowing the neurons to return to a quiescent state.
When neurotransmitters are released into the synapse, not all of them can bind to the receptors of the postsynaptic neuron. However, the gap between neurons must be freer of neurotransmitters in signal termination.
Therefore, the neurotransmitters are either broken down by enzymes, diffuse away, or reuptake occurs.
Reuptake is a process in which neurotransmitters are taken back into the presynaptic neuron from which they originate.
After this process, they are either returned to the synaptic vesicles until needed again, or they are broken down by enzymes.
A neurotransmitter can affect neurons in three ways: it can excite, inhibit, or modulate them.
Excitatory neurotransmitters– these types have a stimulating effect on the neurons. When a neurotransmitter is excitatory, it increases the likelihood that the neuron will fire an action potential. Examples of these types of neurotransmitters are epinephrine and norepinephrine.
Inhibitory neurotransmitters– In contrast to excitatory neurotransmitters, inhibitory neurotransmitters have the opposite effect, they inhibit/hinder the neurons. When a neurotransmitter is inhibitory, it reduces the likelihood that the neuron's action potential will fire. Examples of these types of neurotransmitters are GABA and endorphins.(Video) Neurotransmitters: Type, Structure, and Function
- Modulatorische Neurotransmitter– these are often referred to as neuromodulators. When a neurotransmitter is a neuromodulate, it means that it can affect a large number of neurons at once and affect the action of other neurotransmitters. Neuromodulators do not directly activate the receptors on neurons, but work with neurotransmitters to enhance the excitatory or inhibitory responses of the receptors. Examples of these types of neurotransmitters are serotonin and dopamine.
Whether a neurotransmitter is excitatory or inhibitory depends 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 because there isn't just one receptor for each type of neurotransmitter.
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.
The monoamine group of neurotransmitters is particularly important to psychologists because they are involved in a range of behaviors including decision making, emotional response, happiness, depression, andreward response.
Types of monoamines are serotonin, epinephrine, norepinephrine and dopamine.
Serotonin plays a role as a neurotransmitter as well as a hormone. It is important for mood control and therefore can affect a person's level of happiness. Serotonin is also important in regulating anxiety, appetite, and pain controlsleep cycles.
Serotonin is found in the enteric nervous system in the gastrointestinal (gut) tract, but is also produced in the central nervous system in an area of the brainstem called the raphe nuclei. Serotonin belongs to the class of inhibitory neurotransmitters because it does not stimulate the brain.
Instead, it balances out the excessive excitatory neurotransmitter effects. A lack of serotonin can be associated with thisDepression, sadness, fatigue, suicidal thoughts and anxiety. It therefore plays a role in the underlying cause of many mental health problems.
Serotonin syndrome is a condition where there is too much serotonin in the brain. This can be caused by a reaction to medicines, causing symptoms such as agitation, hallucinations and confusion and can be fatal.
This neurotransmitter and hormone is also known as adrenaline. This is a stress hormone released into the bloodstream via the adrenal glands. This is an excitatory class of neurotransmitter as it stimulates the central nervous system. When there is too much adrenaline in the bloodstream, it can lead to high blood pressure, anxiety, insomnia, and an increased risk of stroke. However, when there was too little adrenaline, it can cause arousal to wane and an inability to respond appropriately in stressful situations, reducing the stress response.
This neurotransmitter is also produced in the adrenal glands and is a naturally occurring chemical also known as norepinephrine. This is an excitatory neurotransmitter as it stimulates the brain and body and is also produced in the brainstem and hypothalamus.
This chemical helps activate the body and brain to take action in times of stress or in dangerous situations.
It's especially prevalent during the fight-or-flight response and helps with alertness. Norepinephrine is highest during times of stress but lowest during sleep cycles.
Too high norepinephrine levels can lead to high blood pressure, excessive sweating and anxiety. Low levels of this chemical can mean lower energy levels, lack of focus, and can also contribute to feelings of depression.
Dopamineis produced in areas of the brain called the substantia nigra, ventral tegmental area, and hypothalamus, which project to the frontal cortex and the nucleus accubens (responsible for reward and pleasure), among others.
Dopamine is both an excitatory and inhibitory neurotransmitter, as well as a neuromodulator involved in reward, motivation, and addiction. An excess of dopamine can lead to competitive behavior, aggression, poor impulse control, gambling and addiction.
As such, addictive substances can increase dopamine levels and encourage the person to continue using those drugs to get that pleasure reward. A lack of dopamine can lead to depression.
It's thought that dopamine may also play a role in coordinating body movements, and its deficiency can be seen in people with Parkinson's disease - leading to tremors and motor impairments.
Gamma-aminobutyric acid (GABA)
GABA is a naturally occurring neurotransmitter known to be the body's primary inhibitory messenger. GABA is localized to many brain regions: hippocampus,Thalamus, basal ganglia, hypothalamus and cerebral vapor.
Its main functions are the regulation of anxiety, vision and motor control. People who don't have enough GABA may find that they have poor impulse control and can lead to seizures in the brain.
A lack of GABA can also lead to mental health issues such as bipolar disorderMania. However, when there is too much GABA, it can lead to hypersomnia (oversleeping) and lack of energy.
Another amino acid is glutamate, which supports cognitive functions such as memory formation and learning. This is known to be the most abundant neurotransmitter found in the central nervous system.
Glutamate is an excitatory neurotransmitter with receptors found in the central nervous system in the neurons and glia. Excess glutamate can lead to excitotoxicity — which means neurons are killed due to overactivation of glutamate receptors.
When these neurons are destroyed, it can lead to diseases like Alzheimer's, stroke and epilepsy.
If there is too little glutamate, this can lead to psychosis, insomnia, difficulty concentrating, mental exhaustion or even death.
This is an inhibitory type of neurotransmitter that decreases 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 a similar way.
Endorphins are primarily produced in the hypothalamus and pituitary gland in response to pain, but can also be released upon completion of physical activity (contributing to a "runner's high").
There aren't many known symptoms of too much endorphins, but it could lead to an addiction to exercise. A lack of endorphins can lead to depression, headaches, anxiety, mood swings, and a condition called fibromyalgia (chronic pain).
Adenosine is a neuromodulator type of neurotransmitter that suppresses arousal and improves sleep cycles. Adenosine is commonly found in the presynaptic regions of the hippocampus and acts as an acentral nervesystemtranquilizers.
Consistently high levels of this neurotransmitter can cause hypersensitivity to touch and heat.
When there is too little adenosine, it can lead to anxiety and trouble sleeping. Caffeine is what is known as an adenosine blocker, which blocks the adenosine receptors. Because of this, caffeine can cause insomnia and it is not recommended to drink it late in the day.
Another type of purine found in the central nervous system and peripheral nervous system. ATP plays a role in autonomic control, sensory transduction, and communication with glial cells.
It essentially transports energy between cells by being released from activated neurons and passed to other active neurons in the brain. ATP is excitatory in several brain regions such as the hippocampus andsomatosensory cortex.
Acetylcholine is the only known neurotransmitter of its kind, found in both the central and nervous systemsparasympathetic nervous system. The main function of this type focuses on muscle movement, memory and learning associated with motor neurons.
Too much acetylcholine is associated with increased salivation, muscle weakness, blurred vision, and paralysis.
Insufficient acetylcholine is linked to learning and memory disorders and has been linked to dementia and Alzheimer's disease according to research (Haam & Yakel, 2017; Tabet, 2006).
Disorders related to neurotransmitters
Symptoms associated with mental illnesses such as mood and anxiety disorders andschizophreniaThey are thought to be due in part to an imbalance in neurotransmitter levels in the brain.
In anxiety disorders, this may reflect reduced GABA activity in the brain and an imbalance in its receptors. It has also been shown to be related to an imbalance in serotonin and norepinephrine responses. Similarly, there is also evidence that there may be links to increased glutamate excitability in people with anxiety.
In depression, there is evidence of abnormalities in noradrenergic, dopaminergic, and serotonergic transmission. Overall, serotonin has been shown to play a rolemood swingsas well as obsessive-compulsive disorder (obsessive compulsive disorder).
Finally, dopamine levels have been shown to be associated with addiction and schizophrenia. Dopamine receptor sensitivity, or too much dopamine, has been suggested to be associated with schizophrenia (Martin, Ressler, Binder & Nemeroff, 2009).
The Effect of Drugs
Different types of drugs can affect chemical transmission and change the way neurotransmitters work. This can include medications used to relieve the symptoms of certain mental illnesses, such as SSRIs, benzodiazepines, and antipsychotics. Neurotransmission can also be affected by illicit drugs such as cocaine, marijuana, and heroin.
- Selective serotonin reuptake inhibitors (SSRIs) are one type ofAntidepressantto relieve symptoms of conditions such as depression, anxiety, post-traumatic stress disorder, panic disorder, obsessive-compulsive disorder and phobias.
SSRIs work by blocking the reuptake of the neurotransmitter serotonin into the neuron that released it. This means that serotonin accumulates in the synaptic cleft, making it more likely that serotonin will reach the receptors of the nearest neurons.
- Benzodiazepines work by reducing the excitability of nerve signals in the brain, primarily in people suffering from insomnia, anxiety, panic disorders, and certain types of epilepsy.
These drugs work by increasing the brain's response to GABA, which has a relaxing and calming effect on the individual. Benzodiazepines are usually only prescribed for a few weeks because they can have adverse side effects by causing more anxiety or altering mood and behavior.
- Antipsychotic medications are typically used to treat the positive symptoms associated with psychosis (eg, delusions, hallucinations, and paranoia), primarily in patients with diagnosed schizophrenia.
Because people with schizophrenia usually have too much dopaminergic activity, antipsychotic drugs work to antagonize dopamine receptors. Antipsychotics can also be used in people with dementia, bipolar disorder, and major depressive disorder.
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 dopamine levels.
Heroin binds to the opioid receptors and triggers the release of extremely high levels of dopamine. The more heroin used, the more likely it is that tolerance will develop, meaning the brain won't function as it did before starting the drug.
This can cause dopamine levels to drop when the drug is stopped, which can ultimately cause that drug to become addictive, allowing the user to feel the dopamine "high" again.
Cocaine is a stimulant because it speeds up the central nervous system, increasing heart rate, blood pressure, alertness, and energy. Cocaine essentially gives the brain a fast-acting dopamine rush. The effects of cocaine do not usually last very long and can leave a person irritable or depressed afterwards, leading to a craving for more.
Cocaine can be highly addictive as it affects dopamine levels and the brain's reward system. Ecstasy is a psychoactive drug that acts as both a stimulant and a hallucinogen. Ecstasy works by binding to and stimulating serotonin receptors and affecting norepinephrine and dopamine.
Ecstasy can induce feelings of joy and warmth, and overall reduce anxiety in the moment. However, regular use and after-effects can increase anxiety, irritability, trouble sleeping, and feelings of depression.
About the author
Olivia Guy-Evans received her bachelor's degree in Educational Psychology from Edge Hill University in 2015. She then received her Masters degree in Educational Psychology from the University of Bristol in 2019 Bristol the last four years.
To reference this article:
To reference this article:
Guy-Evans, O. (2021, 21. Februar).Neurotransmitters: types, function and examples. Just psychology. www.simplypsychology.org/neurotransmitter.html
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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 in Alzheimer's: Anti-Inflammatory Drugs in Acetylcholine Clothing!.Age and age, 35(4), 336-338..
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Guy-Evans, O. (2021, 21. Februar).Synapse definition and function. Just psychology. www.simplypsychology.org/synapse.html
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