By Olivia Guy-Evans, published April 20, 2021 Show by Saul Mcleod, PhD Key Points
Neurotransmitters are important in boosting and balancing signals in the brain and for keeping the brain functioning. They help manage automatic responses such as breathing and heart rate, but they also have psychological functions such as learning, managing mood, fear, pleasure, and happiness. How Neurotransmitters WorkIn order for neurons to 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.
The neuron which released 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. When a nerve impulse (or action potential) triggers the release of neurotransmitters, these chemicals are then released into the synapse and then is taken up by the receptors on the next neuron. This process is known as neurotransmission. For Example
After NeurotransmissionThe 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.
Therefore, the neurotransmitters either get broken down by enzymes, diffused away, or re-uptake occurs. Re-uptake is a process whereby neurotransmitters get reabsorbed back into the presynaptic neuron they came from. After this process, they either get restored back into the synaptic vesicles until needed again, or they get broken down by enzymes. ClassificationA 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. TypesThere 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. Monoamines
Type of monoamines are serotonin, epinephrine, norepinephrine, and dopamine. Serotonin Serotonin plays a role as a neurotransmitter, as well as a hormone. It is important in controlling mood and can therefore affects the happiness levels of an individual. Serotonin is also important for regulating anxiety, appetite, pain control, and sleep cycles. Serotonin is found in the enteric nervous system in the gastrointestinal tract (the gut) but is also produced in the central nervous system in 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 to depression, sadness, fatigue, suicidal thoughts, and anxiety. It therefore plays a role in the underlying cause of many mental health issues. Serotonin syndrome is a condition whereby there is too much serotonin in the brain. This could be caused by a reaction to drugs, leading to symptoms of restlessness, hallucinations, and confusion, and could be fatal. Epinephrine This neurotransmitter and hormone are also known as adrenaline. This is a stress hormone which is released into the blood stream 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 blood stream, 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. Dopamine Dopamine is produced in areas of the brain called the substantia nigra, ventral tegmental area, and the hypothalamus, projecting to the frontal cortex and the nucleus 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 deficiency in dopamine 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. Amino AcidsGamma-aminobutyric acid (GABA) GABA is a naturally occurring neurotransmitter which is known as the body’s primary inhibitory messenger. 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 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 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. PeptidesEndorphins 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). PurinesAdenosine Adenosine is a neuromodulator type of neurotransmitter which functions in suppressing arousal and improving sleep cycles. 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) Another type of purine, found in the central nervous system and the peripheral nervous system. ATP has a role in autonomic control, sensory transduction, and communication with glia cells. It essentially carries energy between cells through being released by activated neurons and passed onto other active neurons in the brain. ATP is excitatory in several brain regions such as the hippocampus and somatosensory cortex. AcetylcholineAcetylcholine 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). Disorders Associated with NeurotransmittersSymptoms associated with mental health conditions such as mood and anxiety disorders and schizophrenia are believed to be the result in part from an imbalance of neurotransmitter levels in the brain. With anxiety disorders, this 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 in mood disorders as 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
Medication
Illicit DrugsDepending 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 afterwards, leading to a craving of more. Cocaine can be highly addictive due to the way it affects the dopamine levels and reward system of the brain. Ecstasy is a psychoactive drug, which works as a stimulant as well as a hallucinogenic. Ecstasy works by binding to serotonin receptors and stimulating them, as well as influencing norepinephrine and dopamine. 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. Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years. How to reference this article:Guy-Evans, O. (2021, Feb 21). Neurotransmitters: types, function and examples. Simply Psychology. www.simplypsychology.org/neurotransmitter.html APA Style ReferencesBoto, 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 . Cherry, K. (2020, November 24). The Role of Neurotransmitters. Very Well Mind. https://www.verywellmind.com/what-is-a-neurotransmitter-2795394#types. Guy-Evans, O. (2021, February 21). Synapse Definition and Function. Simply Psychology. www.simplypsychology.org/synapse.html Home | About Us | Privacy Policy | Advertise | Contact Us Simply Psychology's content is for informational and educational purposes only. Our website is not intended to be a substitute for professional medical advice, diagnosis, or treatment. © Simply Scholar Ltd - All rights reserved |