Researcher & Writer: Lauren Tam
Illustrator: Sanaa Sethi
We have all experienced emotional surges. Have you ever pondered the origins of our emotional torrents? What hidden forces drive these surges within us? The answer lies in neurotransmitters. By delving into the physical mechanisms behind the psychological mind, we gain insight into the connection between brain chemistry and emotions.
What are neurotransmitters?
Our nervous system houses a wide network of nerves that work to send and receive messages throughout our body. At the heart of this intricate communication system, neurotransmitters emerge as the messenger of chemical messages, directing them throughout our system. They govern a multitude of bodily functions, from enabling us to feel sensations to keeping our hearts beating. The ebb and flow of our thoughts, feelings, and actions are all orchestrated by the efforts of these neurotransmitters.
Where are Neurotransmitters Located?
Neurotransmitters are located in a part of the neuron called the axon terminal, which is the end of (terminal) an extension from the neuron cell body (axon). They are stored within thin-walled sacs called synaptic vesicles. These sacs contain thousands of neurotransmitter molecules, patiently waiting for their call to action.
Categories of Neurotransmitters
Experts have identified over 100 types of neurotransmitters to date, with the promise of new discoveries on the horizon. Due to their complicated and multifaceted nature, they have many different roles. Some are compatible with each other, while some bud heads.
Neurotransmitters are grouped into 3 big categories based on their actions, which are very much implicit within their names:
1. Excitatory neurotransmitters encourage a target cell to take action.
2. Inhibitory neurotransmitters decrease the chances of the target cell taking action. In some cases, they have a relaxation effect.
3. Modulatory neurotransmitters send messages to many neurons at the same time. They also communicate with other neurons.
Types of Neurotransmitters
Under these 3 categories, there are many different types of neurotransmitters. Many of their roles seem to overlap, but the different combinations of these roles allow them to perform a specific effect on the brain. Here are some of the most discussed by neuroscientists:
Acetylcholine: the Maestro of Muscle Contraction
Stepping into the limelight as the first neurotransmitter to be discovered, acetylcholine (Ach) plays a pivotal role in an array of bodily functions. Its influence extends to triggering muscle contractions, translating impulses into tangible actions. But its reach doesn't end there – Ach also governs salivary and sweat glands, orchestrates our heartbeat, and even enhances our memory. A deficiency of acetylcholine lies at the heart of Alzheimer's disease, underscoring its profound impact on our cognitive well-being.
Dopamine: the Pathway to Reward
The popular dopamine (DA) is the elixir of motivation, pleasure, and reward-seeking behaviours. Essential for memory, motivation, and behaviour, dopamine's delicate balance is crucial. However, dysregulation of dopamine can wreak havoc on our emotional balance, contributing to mood disorders such as depression and substance abuse. Remarkably, exercise has been shown to elevate dopamine signalling, offering a glimmer of hope to those grappling with early Parkinson's disease.
Serotonin: the Calming Mood Regulator
Known for its calming effect, serotonin (5HT) is an inhibitory neurotransmitter which performs an opposite role to that of dopamine. Serotonin receptors are present throughout the brain and interact with various brain regions involved in emotional processing. By binding to these receptors, serotonin helps regulate mood, cognition, and social behaviour. Imbalances in serotonin are believed to contribute to the development of depressive symptoms, including persistent sadness, loss of interest, and changes in appetite and sleep patterns.
GABA: The Anxiety Regulator
Commonly known as GABA, gamma-aminobutyric acid (GABA) is the central nervous systems’ main inhibitor. This anxiety-relieving amino acid acts by reducing neuronal excitability, promoting relaxation, and countering the effects of excitatory neurotransmitters. Diminished GABA activity or impaired GABA receptors can unleash a storm of heightened anxiety, and contribute to conditions such as anxiety disorders, epilepsy, and insomnia.
HPA Axis: The Stress Respondent
While being one of the lesser known, the hypothalamic-pituitary-adrenal (HPA) axis is a crucial neuroendocrine system that coordinates the body's response to stress. During times of stress, the hypothalamus (a region of the forebrain) releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to secrete adrenocorticotropic hormone (ACTH). ACTH then triggers the release of cortisol, the primary stress hormone, from the adrenal glands. Cortisol helps the body mobilise energy and cope with stress. Elevated cortisol levels resulting from chronic stress have been associated with increased risk of anxiety, depression, and other mood disorders.
Disorders associated with Neurotransmitters
Within the tapestry of our neurochemical mechanisms, imbalances can give rise to a plethora of disorders that shape the human experience.
Schizophrenia: Schizophrenia casts a shadow over the lives of those affected, manifesting as a complex interplay of hallucinations, delusions, and disordered thinking and behaviour. One prevailing theory suggests a link between the disorder and abnormalities in dopamine receptor sensitivity or excessive dopamine levels.
Epilepsy: Epilepsy is a disorder of the brain characterised by repeated seizures (a sudden alteration of behaviour). In patients with epilepsy, the brain’s normal electrical pattern is disrupted by sudden and synchronised bursts of electrical energy that may briefly affect their consciousness, movements or sensations.
Multiple sclerosis: Multiple sclerosis can affect the brain and the spinal cord (the central nervous system), wreaking havoc on the protective coating on the nerve fibres known as myelin. This gives rise to a wide range of symptoms, including problems with vision, arm or leg movement, sensation or balance.
Autism: Autism spectrum disorder is a neurological disorder that affects the patient’s interaction, communication, learning and behaviour. While the primary causes of autism remain elusive, researchers have uncovered tantalising clues suggesting a complex interplay between genetic factors and environmental influences. These aspects include having older parents, certain genetic conditions e.g. Down syndrome, and having a very low birth weight.
Depression: While common, depression is a serious mood disorder that causes severe symptoms, affecting how a person feels, thinks, and handles daily activities, such as sleeping, eating, or working. This formidable foe manifests in various forms. Some are classified by intensity (persistent depressive disorder, major depression, and depression with symptoms of psychosis), while others are specific to certain factors (seasonal affective disorder and perinatal depression).
Fun Fact: Women are diagnosed with depression more often than men, but because men may be less likely to recognize, talk about, and seek help for their feelings or emotional problems, they are at greater risk of depression symptoms being undiagnosed or undertreated.
Anxiety: Similar to depression, anxiety is a serious mental health condition characterised by excessive worry, fear, and unease. Types include generalised anxiety disorder (persistent worry), panic disorder (sudden fear attacks), social anxiety disorder (fear of social situations), and post-traumatic stress disorder (trauma-related symptoms). As with depression, men's reluctance to acknowledge and seek help for anxiety may lead to undiagnosed or undertreated symptoms.
Medication
In the pursuit of restoring neurochemical harmony, medications play a pivotal role, offering relief and respite for those grappling with neurotransmitter imbalances.
Selective Serotonin Reuptake Inhibitors (SSRIs) are antidepressants used to alleviate symptoms of depression, anxiety, post-traumatic stress disorder, panic disorder, and phobias. By blocking the reuptake of serotonin, they foster a buildup of this neurotransmitter in the synaptic cleft, making it more likely that serotonin will reach the receptors of the next neuron.
Benzodiazepines work by enhancing the brain’s response to GABA. With their soothing and calming effects, benzodiazepines offer solace to individuals grappling with insomnia, anxiety, panic disorder, and certain types of epilepsy.
Antipsychotic medications are usually used to treat the positive symptoms associated with psychosis (e.g. delusions, hallucinations, and paranoia), primarily in those diagnosed with schizophrenia. As discussed, schizophrenic patients have excessive dopamine. Therefore, antiseptics work to antagonise dopamine receptors.
All in all, understanding neurotransmitters is crucial for comprehending the connection between brain chemistry and psychological well-being. Balancing neurotransmitter levels is key to promoting optimal mental health.
Bibliography
Berry, J. (2019, October 12). Neurotransmitters: What they are, functions, and psychology. Medical and Health Information; Medical News Today. https://www.medicalnewstoday.com/articles/326649
Epilepsy – Seizure Types, Symptoms and Treatment Options. (n.d.). American Association of Neurological Surgeons. Retrieved September 8, 2023, from https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Epilepsy#:~:text=Epilepsy%20is%20a%20disorder%20of,impulses%20in%20an%20orderly%20pattern.
Felton, A. (9 C.E.). Neurotransmitters: What To Know. WebMD; WebMD. https://www.webmd.com/brain/neurotransmitters-what-to-know#1-6
MSc, O. G.-E. (2022, November 3). Neurotransmitters: Types, Function and Examples - Simply Psychology. Simply Psychology. https://www.simplypsychology.org/neurotransmitter.html
NIMH » Autism Spectrum Disorder. (n.d.). National Institute of Mental Health (NIMH). Retrieved September 8, 2023, from https://www.nimh.nih.gov/health/topics/autism-spectrum-disorders-asd#:~:text=Autism%20Spectrum%20Disorder-,Overview,first%202%20years%20of%20life.
NIMH » Depression. (n.d.). National Institute of Mental Health (NIMH). Retrieved September 8, 2023, from https://www.nimh.nih.gov/health/topics/depression#:~:text=Depression%20
Schizophrenia - Symptoms and causes - Mayo Clinic. (2020, January 7). Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/schizophrenia/symptoms-causes/syc-20354443#:~:text=Schizophrenia%20is%20a%20serious%20mental,with%20schizophrenia%20require%20lifelong%20treatment.
website. (23 C.E.). Multiple sclerosis - NHS. Nhs.Uk. https://www.nhs.uk/conditions/multiple-sclerosis/#:~:text=Multiple%20sclerosis%20(MS)%20is%20a,it%20can%20occasionally%20be%20mild.