Neurotransmitter s

8/14/2019 Neurotransmitter s

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Neurotransmittereurotransmitters

The Heart of Matter


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Among the many relevant phenolderivatives, the catechol neurotransmitters aresome of the most valuable and interesting.


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The nervous system runs on a series of physical andchemical reactions. Signals are carried from one nerve cell to

another by simple chemical molecules known asneurotransmitters. Epinephrine (adrenalin), norepinephrine,dopamine, and acetylcholine are but four of the more than 20known neurotransmitters.

The first three substances are also called catecholamines because they aresimilar to catechol, or o-hydroxyphenol


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The sympathetic nervous system (SNS)and the parasympathetic nervous system(PNS) stimulate almost every organ in the

body in a complementary fashion. The PNSsupplies the stimulation for normalphysiological functions, while the SNSprovides the necessary arousal for survival

in the cold, cruel world.


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The PNS is responsible for contraction ofthe pupils of the eyes, normal pulse andblood pressure, constriction of the bronchi,digestive enzyme-containing secretions in

the mouth, and increased gastrointestinalactivity. The SNS in an effort to make thebody alert and ready to respond to anyoutside threat, causes dilation of the pupils,

increased pulse and blood pressure, andrelaxation of the bronchi, dry mouth, anddecreased gastrointestinal motility.


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The prime neurotransmitter in the SNS isnorepinephrine. It is synthesized in an SNSnerve cell and, in response to a nerve impulse,is secreted into the space between two nerve

cells, called the synapse. The neurotransmittertravels to the other side of the synapse andcombines with a protein known as a receptoron the surface of the next nerve cell. This

triggers the nerve impulse in that cell.


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Molecules that are similar in structure to anatural neurotransmitter can either stimulate anerve cell just like the natural chemical(agonists) or bind to the receptor without

stimulation and block the access of the normalneurotransmitter (antagonists).

Agonist-receptor complex stimulates nerve transmission.

Antagonist-receptor complex causes no nervestimulation and blocks normal stimulation.


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Amphetamines and decongestants areexamples of SNS agonists. Although thesedrugs may be used for certain specific effects,such as in dieting and for nasal congestion,respectively, it is important to remember thatthey are similar to the naturalneurotransmitters that generally affect the SNSand also the central nervous system, which isfar too complex to discuss in this space. Thus

the warnings on the containers for many over-the-counter medications should be heeded,especially if the consumer has a preexistingcondition such as high blood pressure,

diabetes, or glaucoma.


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Another aspect of drug use involves thedesign of neurotransmitter antagonists, as inthe treatment of heart disease. Many types ofneurotransmitter receptors exist, some of

which are concentrated in specific tissues, suchas heart tissue (1-receptors) and bronchial

tissue (2-receptors). 1-blockers have been

designed to antagonize the nerve signals to the

heart without having an effect of equalintensity on breathing.


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Conversely, a drug that is specific for 2-receptors could be used as an agonist torelieve asthma without worsening an existingcardiac condition.

The treatment of disease had reached amolecular level, leading to more potent andspecific drugs with the possibility of living alonger and more enjoyable life.


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-blockers:


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2-receptor agonists:

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Neurotransmitter s