Neurotransmitters

Module 5 – Emotions Where do emotions come from? The emotional brain Neurotransmitters

Besides the circuits and structures of the emotional brain in general, and of the limbic system in particular, there is a special group of substances, known as “neurotransmitters”, that contributes greatly to the generation, processing and communicating of emotions.

Watch the video. What is a neurotransmitter? How does it work? Which neurotransmitters were mentioned as examples and what are some of their most important functions?

What is a neurotransmitter?

“Neurotransmitter (Sembulingam et al, 2013, 787-791) is a chemical substance that acts as a mediator for the transmission of nerve impulse from one neuron to other neuron through a synapse¹. It is produced in the cell body of the neuron and is transported through axon². At the axon terminal, the neurotransmitter is stored in small packets called vesicles. Under the influence of stimulus, these vesicles open and release the neurotransmitter into synaptic cleft. It binds to the specific receptors on the surface of post synaptic cell and is responsible for the various actions produced. In short, neurotransmitters are the way nerve cells communicate with each other and with other cells in the body. Neurotransmitters are used to relay information about environment to the brain, to analyze the information and to set in motion appropriate bodily responses.( Clark, 2004, 137)” (Uppala et al. 2015, 6633)

At the end of each neuron, there is a tiny gap, called a synapse.
An axon, also called nerve fibre, is portion of a nerve cell (neuron) that carries nerve impulses away from the cell body. A neuron typically has one axon that connects it with other neurons or with muscle or gland cells. Some axons may be quite long, reaching, for example, from the spinal cord down to a toe.

Process of neurotransmission

According to their function, neurotransmitters are classified into two types: excitatory neurotransmitters and inhibitory neurotransmitters.

Excitatory neurotransmitters are responsible for the conduction of impulse from presynaptic neuron to postsynaptic neuron. Neurotransmitter released from presynaptic axon terminal causes some change in resting membrane potential, i.e. slight depolarization by the opening of sodium channels in the postsynaptic membrane and influx of sodium ions from extra cellular fluid. This slight depolarization is called excitation. (Uppala et al.2015, 6633).

Excitatory neurotransmitters are in charge of energy, alertness, motor movement, fight or flight response, and higher order thinking, all of which influence our emotions. Some common excitatory neurotransmitters are acetylcholine, noradrenaline, glutamate, aspartate, histamine and nitric oxide.

Inhibitory neurotransmitters suppress the conduction of impulse from the presynaptic neuron to postsynaptic neuron. They calm the brain and help create balance in mood. In other words, decreasing the probability of an excitatory signal being sent, these neurotransmitters act as the human body’s nervous system off switch. The balance between excitation and inhabitation is very important as too much excitement can lead to insomnia, restlessness, and irritability. Inhibitory neurotransmitters contribute to the decrease of aggression, encourage calmness, and induce sleep, which in turn influence our emotions. Some common inhibitory neurotransmitters are dopamine, gamma amino butyric acid (GABA), glycine and serotonin.

In addition to the above classification, neurotransmitters can also be classified based on their chemical structure:

Amino acids – GABA, glutamate
Monoamines – serotonin, histamine
Catecholamines (subcategory of monoamines) – dopamine, norepinephrine, epinephrine
Peptides – oxytocin, endorphins

Scheme of neurotransmission

If you want to read more about the neurotransmitters:

Uppala, A. et al. (2015). Impact of Neurotransmitters on Health through Emotions. Int J Recent Sci Res. 6(10), pp. 6632- 6636.
Hughes, J. et. al. (2004). Selective effects of simultaneous monoamine depletion on mood and emotional responsiveness. International Journal of Neuropsychopharmacology, 7(1), 9-17.

SOME IMPORTANT NEUROTRANSMITTORS AND THEIR FUNCTIONS

Serotonin (5-HT), dopamine (DA), norepinephrine (also known as noradrenaline) (NE) are the three major monoamine neurotransmitters.

Serotonin (5-HT)

It is a hormone and neurotransmitter and is involved in regulating and modulating:

mood,
sleep / wake states
appetite
“preventing depression and promoting motivation” (McKenna & Lim, 2012).

When levels of this neurotransmitter are low, an individual experiences problems with attention, becomes unorganized, and lacks concentration. Consequently, all this makes an individual to experience negative emotional states.

When levels of this neurotransmitter are high, this can result in a life-threatening disorder known as Serotonin Syndrome (SS). SS produces malignant hyperthermia, over-confidence, aggression and agitation.

Serotonergic cell bodies originate generally in the midbrain and upper pons area, with neurons projecting to the cerebral cortex, basal ganglia, and the limbic system (Kaplan, Middleton, Urban, & Midgley, 2002).

Dopamine (DA)

It is involved in: Main dopamine pathway in the brain

the brain’s reward system, which generates the feeling of pleasure, and acts as the brain’s “feel good”
motivation,
addictions (Tortora & Derrickson, 2014).
coordinating body movements (motor functions of the body)

It has the capability to act as either an inhibitory or excitatory neurotransmitter, depending upon the particular site it binds to, and can alter our emotional states.

As dopamine levels are increased when we take part in activities that bring us satisfaction and pleasure, too high of a level can become detrimental for our health. Disproportionate higher levels can cause us to become hyper-stimulated to our surrounding environment or cause a disrupted thought, which are all characteristics of schizophrenia.

Dopamine’s dysfunction is involved in psychiatric disorders, including drug addiction, schizophrenia, Parkinson’s and Huntington’s disease. (Niyonambaza et al, 2019). For instance, Parkinson’s disease, which is a degenerative disease that results in tremors and motor movement impairments, is caused by the loss of dopamine-generating neurons in the brain.

Low levels of dopamine are associated with a lack of focus, cognitive problems such as memory and learning deficits, compulsions, addiction, and a loss of satisfaction in previously enjoyable activities. This can have a substantive impact upon an individual’s emotional state.

Norepinephrine (NE)

Norepinephrine (NE) (also known as noradrenaline) is involved in:

the body’s fight or flight response – mobilizing the body and brain to take actions in situations of danger and stress(Johnson et al., 2011) (Schachter, 1957);
creating a sense of urgency, overpowering fear;
increasing heart rate and blood pressure (Summer & Bloor, 1984; Passetti, Dalley, O’Connel, Everett& Robbins, 2000)

It is also a hormone when released from the adrenal glands (McKenna & Lim, 2012).

Emotionally, this neurotransmitter in the brain is related to both depression, and anxiety. Almost all anxiety disorders involve high levels of noradrenaline.

As noradrenaline is the neurotransmitter of arousal, low levels are linked with poor memory, depression, below average levels of alertness, and interest.

Additionally, moderately high levels of noradrenaline produce uncomfortable feelings of arousal which strongly influence physical changes, intensify anxiety, impair concentration, and increases the startle reflex. This system begins from the locus coeruleus, lateral tegmental area located in the brainstem, in which through axonal pathways to the cortex, reaches the central nervous system(CNS).

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