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Course: Mental Health Nursing

Topic: Function of Major Neurotransmitters

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Module Goals

Learners will be able to:

Summarize the role of neurotransmitters in specific regions of the brain.
Interpret the influence of neurotransmitters on functional behavior.
Determine the relationship between dysfunctional behavior and specific neurotransmitters.

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What is Neurotransmitter?

Endogenous chemicals that allow neurons to communicate with each other or with muscles.
Chemical messengers integral in shaping everyday life functions.
Influence neurons in three ways:

Excitatory: Encourage target cells to take action.
Inhibitory: Inhibits target cells from taking action.
Modulatory: Modulates the effectiveness of a neurotransmitter by influencing its release or receptor response to it.

Sheffler et al, 2021

University of Queensland, n.d.

American Psychological Association, n.d.

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Neurotransmission

Required to regulate body function such as:

Heart rate
Breathing
Sleep cycles
Digestion
Mood
Concentration
Appetite
Muscle movement

Neurotransmitters relay messages by attaching to specific receptors on the target cells.

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Neurotransmission Pathway

University of Queensland, n.d.

Communication between two neurons happens in the synaptic cleft.

Electrical signals from the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron

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Major Neurotransmitters

Acetylcholine
Dopamine
Serotonin
Norepinephrine
Glutamate
Gamma-aminobutyric acid (GABA)

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Acetylcholine

Primarily an excitatory neurotransmitter, and neuromodulator as well.
Present at all autonomic ganglia, at many autonomically innervated organs, at the neuromuscular junction, and at many synapses in the central nervous system (CNS).
Functions:

Triggers muscle contractions
Stimulates some hormones
Controls heartbeat

Has involvement in memory, motivation, arousal, and attention.

Sam & Bordini, 2021

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Acetylcholine Function in Brain

Sam & Bordini, 2021

Originates from two major places in the brain.

Basal forebrain
Mesopontine tegmentum area

Essential in neocortex to learn simple tasks of discrimination.

Absence of acetylcholine in the hippocampus causes forgetfulness.

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Critical Thinking Question

Absence of acetylcholine in the hippocampus may cause which of the following? (Select all that apply)

Headaches
Changes in heartbeat
Forgetfulness
Changes in color perception
Sleeplessness

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Dopamine

Dopaminergic neurons principally found in:

Ventral tegmental area (VTA) of the midbrain
Substantia nigra pars compacta
Arcuate nucleus of hypothalamus

Essential role in several brain functions

Behaviors involving motivation, punishment, and reward
Cognitive functions involving attention, learning, and working (short-term) memory
Voluntary movement
Pain processing
Sleep and dreaming
Mood regulation

Juárez Olguín et al., 2015

Chaves, 2021

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Dopaminergic Pathway

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Clinical Significance of Dopamine

Low dopamine activity

Muscle rigidity/tremors/spasms
Impairment of fine motor skills
Problems eating/constipation
Fatigue/lack of energy
Cognitive impairment, problem focusing
Mood swings
Low sex drive

Chaves, 2021

High dopamine activity

Anxiety
Excess energy or mania
Increased feeling of stress
Improved focus and learning ability
High sex drives
Anxiety
Insomnia
Aggression
Hallucinations

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Clinical Significance of Dopamine

Level of dopamine increases in brain when body expects a reward
Dopamine related mental health conditions

Addiction
Schizophrenia
Depression
Bipolar disorder
Binge-eating disorder
Tourette syndrome
Attention deficit hyperactivity disorder
Obsessive-compulsive disorder

Movement disorders involving dopamine

Parkinson’s disease
Huntington’s disease
Restless legs syndrome

Chaves, 2021

Sheffler et al, 2021

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Norepinephrine

A monoamine synthesized in CNS and sympathetic nerves.

Locus coeruleus of the brain plays vital role in signaling of norepinephrine.

Its release in the brain exerts effects on variety of processes including stress, sleep, attention, focus, and inflammation.

Plays a role in modulating responses of autonomic nervous system.

Sheffler et al., 2021

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Clinical Significance of Norepinephrine

Involved in pathogenesis of neuropsychiatric disorders when changes occur in:

Locus coeruleus firing
Dysregulation of norepinephrine function
Synaptic receptor regulation
Norepinephrine availability

Conditions related to norepinephrine dysfunction:

Anxiety disorders
Mood disorders
Attention-deficit hyperactivity disorder
Alzheimer’s disease
Posttraumatic stress disorder

Many symptoms in these disorders are directly attributable to norepinephrine dysfunction in neural circuitry.

Sheffler et al., 2021

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Critical Thinking Question

Which client would the nurse expect would be prescribed dopamine?

A client with migraines
A client with Parkinson’s disease
A client who complains of difficulty getting to sleep
A client who exhibits aggressive behavior

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Serotonin

Almost all serotonin is produced by intestines and is required for healthy bodily functions as:

Bowel motility, bladder control, and cardiovascular function.

Raphe nuclei is the primary location for production in the brain.
Present in nine groups of cell bodies isolated to the pons and midbrain, a small number of serotonergic nuclei reside within the medulla.
Functions include sleep, hunger, mood, memory, and learning management.

Bakshi, 2021

Block, 2021

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Serotonergic System

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Serotonin and Mental Health

Mood regulation

Body's natural "feel-good" chemical.
Its influence in mood makes it one of several brain chemicals integral to overall ‘sense of well being’.
Increasing serotonin levels is the purpose of antidepressants known as selective serotonin reuptake inhibitors (SSRIs).

Sleep regulation

Regulates sleep with other neurotransmitters like dopamine, which plays a key role.
Required to make melatonin which is crucial for proper functioning of the sleep cycle.

Block, 2021

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Clinical Significance of Serotonin in Mental Health

Implicated in the pathogenesis of depression.
Research has shown that endogenous depression has low plasma levels of tryptophan (a precursor of serotonin).
Postmortem studies found an association between decreased serotonin levels in the brain and suicide among depressed clients.
Many medications have been developed that target serotonin in the treatment of depression.

Example: Tricyclic antidepressants work by increasing serotonin levels in the synapse.

Sheffler et al., 2021

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Glutamate

Principal excitatory neurotransmitter used in the brain.
Primary mediator of nervous system plasticity.
Made in CNS through the synthesis of glutamine.
Necessary for making gamma aminobutyric acid (GABA), which is a calming neurotransmitter in the brain.
Most brain cells need glutamate to communicate with one another.

Sheffler et al., 2021

Metrus, 2021

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Glutamate Functions

Chemical messenger

Conveys message from one nerve cell to another.

Can be used by brain cells when reserves of glucose, the main source of energy for cells, are low.
Helps strengthen or weaken signals between neurons over time to shape learning and memory.
Higher levels linked to increased sensations of pain.
Sleep and wakefulness mediator.

Metrus, 2021

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Clinical Significance of Glutamate

Symptoms of glutamate deficiency

Insomnia
Difficulty concentrating
Mental exhaustion
Low energy

Symptoms of excessive glutamate

Hyperalgesia (pain amplification)
Anxiety
Restlessness
Symptoms similar to Attention Deficit Hyperactivity Disorder

Metrus, 2021

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NHS UK (2021) lists following as Attention Deficit Hyperactivity Disorder (ADHD) symptoms:

Inattentiveness (difficulty concentrating and focusing)

The main signs of inattentiveness are:

having a short attention span and being easily distracted
making careless mistakes – for example, in schoolwork
appearing forgetful or losing things
being unable to stick to tasks that are tedious or time-consuming
appearing to be unable to listen to or carry out instructions
constantly changing activity or task
having difficulty organising tasks

Hyperactivity and impulsiveness

The main signs of hyperactivity and impulsiveness are:

being unable to sit still, especially in calm or quiet surroundings
constantly fidgeting
being unable to concentrate on tasks
excessive physical movement
excessive talking
being unable to wait their turn
acting without thinking
interrupting conversations
little or no sense of danger

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GABA

Found primarily in spinal cord.
Major inhibitory neurotransmitter accounting for 40% of the inhibitory processing in brain.
Plays a role in how people experience anxiety, fear, and stress.
Appropriate GABA activity.

Calming effect in brain
Promotes healthy stress response by preventing excess neuronal excitation.
In spinal cord, allows for sensory information integration and helps to create smooth movements.

Sheffler et al., 2021

Gans, 2021

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Clinical Significance of GABA in Mental health

Decreased GABA activity is said to contribute to following disorders:

Anxiety disorders
Major depression
Schizophrenia
Autism spectrum disorder

Gans, 2021

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Critical Thinking Question

Which Neurotransmitter is described as the body’s “feel good” chemical?

Serotonin
GABA
Glutamate
Norepinephrine

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References:

American Psychological Association. (n.d.). Neuromodulator. Dictionary.apa.com. Retrieved on October 27, 2021 from https://dictionary.apa.org/neuromodulator

Bakshi, A. (2021, July 31). Biochemistry, Serotonin. In: P. Tadi (Ed.), StatPearls. https://www.statpearls.com/ArticleLibrary/viewarticle/28917

Block, D.B. (2021, April 16). What Is Serotonin? [Review of the article What Is Serotonin?, by Salters-Pedneault, K.]. verywellmind. https://www.verywellmind.com/what-is-serotonin-425327

Chaves, C.(2021, February 15). What is Dopamine? [Review of the article What Is Dopamine?, by Dellwo, A.], verywellhealth. https://www.verywellhealth.com/dopamine-5086831

Gans, S. (2021, October 12). What Is GABA? [Review of the articLe What Is GABA?, by Pugle, M.], verywellhealth. https://www.verywellhealth.com/gaba-5095143

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References:

Juárez Olguín, J. H., Calderón Guzmán, D., Hernández García, E., & Barragán Mejía, G. (2016). The Role of Dopamine and Its Dysfunction as a Consequence of Oxidative Stress. Oxidative medicine and cellular longevity, 2016, 9730467. https://doi.org/10.1155/2016/9730467

Mateos-Aparicio, P. & Rodríguez-Moreno, A. (2019, February 27). The Impact of Studying Brain Plasticity. Frontiers in Cellular Neuroscience. https://www.frontiersin.org/articles/10.3389/fncel.2019.00066/full

Mesolam, M. (2013). Cholinergic circuitry of the human nucleus basalis and its fate in Alzheimer's disease. Journal of Comparative Neurology, 521 (18), 4124-4144. https://onlinelibrary.wiley.com/doi/10.1002/cne.23415

Metrus, N.R. (2021, July 21). What Is Glutamate? [Review of the article What Is Glutamate?, by Pugle, M.]. verywellhealth. https://www.verywellhealth.com/what-is-glutamate-5188294

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References:

NHS UK. (2021, December 24). Symptoms: Attention deficit hyperactivity disorder (ADHD). https://www.nhs.uk/conditions/attention-deficit-hyperactivity-disorder-adhd/symptoms/

Sam, C. & Bordini,B. (2021, April 17). Physiology, Acetylcholine. In: StatPearls [Internet]. StatPearls Publishing. Retrieved on October 27, 2021 from https://www.ncbi.nlm.nih.gov/books/NBK557825/

Sheffler, Z.M., Reddy, V., & Pillarisetty, L.S. (2021, May 9). Physiology, Neurotransmitters. In: StatPearls [Internet]. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK539894/

University of Queensland Australia. (n.d.). What are neurotransmitters?. Retrieved on October 22, 2021 from https://qbi.uq.edu.au/brain/brain-physiology/what-are-neurotransmitters

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