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Neurotransmitter

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Neuron synapse

Neurotransmitters are chemicals that are secreted by neurons (nerve cells) to carry messages to other neurons or other cells like muscles fibers. They are primarily used for stimulating a nerve impulse (action potentials), but they can also be inhibitory. They are extremely important in brain function, muscle contraction, emotion, and even sleep patterns.

Function

Neurotransmitters function primarily within synapses between neurons (nerve cells). Neurotransmitters are required in muscle function because the presynaptic terminal on a nerve does not make contact with the muscle fibers with which it is interacting. Therefore, the nerve has synaptic vesicles that release neurotransmitters. These neurotransmitters then travel across the synaptic cleft where they bind with receptor sites. This bind between the receptor site and the neurotransmitter results in an action potential [1].

Neurotransmitters can generally be broken into two basic types: excitatory and inhibitory. The difference in the two lies in their effect on postsynaptic membranes. Excitatory neurotransmitters are involved in stimulating the brain while inhibitory help maintain balance in the brain. [2]. They accomplish these goals through either depolarization or hyperpolarization. Excitatory neurotransmitters use depolarization, which promotes the generation of action potentials. On the other hand, Inhibitory neurotransmitters use hyperpolarization to slow and eventually inhibit the generation of action potentials [3].

Acetylcholine

The process of acetylcholine being formed from acetylcholinesterase and being broken back down into acetic acid and choline.

Acetylcholine is a very important neurotransmitter being involved in skeletal muscle movement, smooth muscle regulation, and memory. When a nerve impulse (action potential) reaches the end of the neuron (the axon) acetylcholine released by vesicles into the synaptic cleft. It then travels (is "transmitted") across the synaptic cleft where it binds to receptors on the post-synaptic cell where it stimulates an action potential in the muscle or other cell. Once this process is complete, the acetylcholine molecules are recycled by being broken back down into acetic acid and choline. This breakdown allows acetylcholine to be synthesized without a substantial amount of additional help.[4]

Dopamine

Main Article: Dopamine
A diagram showing the various pathways of Dopamine through the brain

Dopamine is another common inhibitory neurotransmitter. Dopamine is related to the pleasure systems of the brain. Dopamine provides feelings of pleasure when doing naturally satisfying things such as eating. However, research has caused some scientists to believe that Dopamine may be involved in desire rather than simply being a "reward chemical." Additionally, Dopamine is also released in the presence of negative stimuli. Studies have also shown that Dopamine may be involved in predicting pleasurable activity. This means that Dopamine may also be integral in the decision making process[5]

Serotonin

Serotonin could possibly be one of the most influential neurotransmitters in the human body. Some of the important functions that serotonin controls include, sleep, temperature regulation, libido (sexual desire)[6], appetite, learning, and even memory [7].

Serotonin occurs naturally in the body. It exists as a monoamine neurotransmitter. It gets into the body through the digestion of foods containing an amino acid known as L-Tryptophan [8]. This explains why serotonin is present in the intestinal membranes [7].

Endorphin

Endorphin is a common type of inhibitory neurotransmitter. The effects involved with endorphin are similar to the effects of the drugs morphine or heroine. Endorphin is also involved in the hibernation patterns of animals. [2] Endorphin has been known to cause what is known as "runner's high." This feeling is common among habitual runners [9] and has been compared to the feeling generated by marijuana use. [10] While there is no concrete evidence that Endorphin causes this feeling, this neurotransmitter is released during periods of moderate exercise.[9]

Problems

Effect of Methamphetamine Use

A brain scan showing dopamine transporter activity during different stages of abstinentence from methamphetamine use

Methamphetamine (or Meth) is a very dangerous stimulant. It is extremely addictive and damaging to users. The problems that surround meth use are directly associated to its effect on neurotransmitters. Meth use causes the brain to release increased amounts of Dopamine while causing less of it to be reabsorbed. This causes there to be more Dopamine in the brain than is necessary. This causes a feeling of euphoria. [11]

Chronic use of methamphetamine causes many problems for the brain. The problems are not only chemical, but also structural. Studies have shown that some of the emotional and cognitive problems come as a result of these structural problems.[11] Long term use can result in the dopamine receptors being destroyed. This destruction of receptors makes it virtually impossible for users to feel any sort of pleasure. [12]

Serotonin's Effect on Mental Health

Serotonin has been considered an integral part of mental health, especially in the context of social behavior, for a long time. However, the precise purpose of serotonin was never entirely clear. Studies have shown that people tend to be more aggressive when they are hungry. It is now believed that this aggression comes from a lack of L-Tryptophan, an amino acid that can only enter the body through food [13]. Serotonin has also been known to have a role in depression. Scientists believe that depression comes from an inbalance of 2 primary neurotransmitters, Serotonin and Norepinephrine. In 1988, new drugs called selective serotonin-reuptake inhibitors (or SSRIs). These drugs help improve the effectiveness of serotonin in the brain by making present serotonin useful to the brain for a longer period of time [14].

Table of transmitters

Category Name Abbreviation Metabotropic Ionotropic
Small: Amino acids Aspartate - -
Neuropeptides N-Acetylaspartylglutamate NAAG Metabotropic glutamate receptors; selective agonist of mGluR3 -
Small: Amino acids Glutamate (glutamic acid) Glu Metabotropic glutamate receptor NMDA receptor, Kainate receptor, AMPA receptor
Small: Amino acids Gamma-aminobutyric acid GABA GABAB receptor GABAA receptor, GABAC receptor
Small: Amino acids Glycine Gly - Glycine receptor
Small: Acetylcholine Acetylcholine Ach Muscarinic acetylcholine receptor Nicotinic acetylcholine receptor
Small: Monoamine (Phe/Tyr) Dopamine DA Dopamine receptor -
Small: Monoamine (Phe/Tyr) Norepinephrine (noradrenaline) NE - -
Small: Monoamine (Phe/Tyr) Epinephrine (adrenalin) Epi - -
Small: Monoamine (Phe/Tyr) Octopamine - -
Small: Monoamine (Phe/Tyr) Tyramine -
Small: Monoamine (Trp) Serotonin (5-hydroxytryptamine) 5-HT Serotonin receptor, all but 5-HT3 5-HT3
Small: Monoamine (Trp) Melatonin Mel Melatonin receptor -
Small: Monoamine (His) Histamine H Histamine receptor -
PP: Gastrins Gastrin - -
PP: Gastrins Cholecystokinin CCK Cholecystokinin receptor -
PP: Neurohypophyseals Vasopressin Vasopressin receptor -
PP: Neurohypophyseals Oxytocin Oxytocin receptor -
PP: Neurohypophyseals Neurophysin I - -
PP: Neurohypophyseals Neurophysin II - -
PP: Neuropeptide Y Neuropeptide Y NY Neuropeptide Y receptor -
PP: Neuropeptide Y Pancreatic polypeptide PP - -
PP: Neuropeptide Y Peptide YY PYY - -
PP: Opioids Corticotropin (adrenocorticotropic hormone) ACTH Corticotropin receptor -
PP: Opioids Dynorphin - -
PP: Opioids Endorphin - -
PP: Opioids Enkephaline - -
PP: Secretins Secretin Secretin receptor -
PP: Secretins Motilin Motilin receptor -
PP: Secretins Glucagon Glucagon receptor -
PP: Secretins Vasoactive intestinal peptide VIP Vasoactive intestinal peptide receptor -
PP: Secretins Growth hormone-releasing factor GRF - -
PP: Somtostatins Somatostatin Somatostatin receptor -
SS: Tachykinins Neurokinin A - -
SS: Tachykinins Neurokinin B - -
SS: Tachykinins Substance P - -
PP: Other Bombesin - -
PP: Other Gastrin releasing peptide GRP - -
Gas Nitric oxide NO - -
Gas Carbon monoxide CO - -
Other Anandamide AEA Cannabinoid receptor -
Other Adenosine triphosphate ATP P2Y12 P2X receptor

Gallery

References