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By the end of this section, you will be able to:
  • List the classes of pharmaceuticals that interact with the autonomic nervous system
  • Differentiate between cholinergic and adrenergic compounds
  • Differentiate between sympathomimetic and sympatholytic drugs
  • Relate the consequences of nicotine abuse with respect to autonomic control of the cardiovascular system

An important way to understand the effects of native neurochemicals in the autonomic system is in considering the effects of pharmaceutical drugs. This can be considered in terms of how drugs change autonomic function. These effects will primarily be based on how drugs act at the receptors of the autonomic system neurochemistry. The signaling molecules of the nervous system interact with proteins in the cell membranes of various target cells. In fact, no effect can be attributed to just the signaling molecules themselves without considering the receptors. A chemical that the body produces to interact with those receptors is called an endogenous chemical    , whereas a chemical introduced to the system from outside is an exogenous chemical    . Exogenous chemicals may be of a natural origin, such as a plant extract, or they may be synthetically produced in a pharmaceutical laboratory.

Broad autonomic effects

One important drug that affects the autonomic system broadly is not a pharmaceutical therapeutic agent associated with the system. This drug is nicotine. The effects of nicotine on the autonomic nervous system are important in considering the role smoking can play in health.

All ganglionic neurons of the autonomic system, in both sympathetic and parasympathetic ganglia, are activated by ACh released from preganglionic fibers. The ACh receptors on these neurons are of the nicotinic type, meaning that they are ligand-gated ion channels. When the neurotransmitter released from the preganglionic fiber binds to the receptor protein, a channel opens to allow positive ions to cross the cell membrane. The result is depolarization of the ganglia. Nicotine acts as an ACh analog at these synapses, so when someone takes in the drug, it binds to these ACh receptors and activates the ganglionic neurons, causing them to depolarize.

Ganglia of both divisions are activated equally by the drug. For many target organs in the body, this results in no net change. The competing inputs to the system cancel each other out and nothing significant happens. For example, the sympathetic system will cause sphincters in the digestive tract to contract, limiting digestive propulsion, but the parasympathetic system will cause the contraction of other muscles in the digestive tract, which will try to push the contents of the digestive system along. The end result is that the food does not really move along and the digestive system has not appreciably changed.

The system in which this can be problematic is in the cardiovascular system, which is why smoking is a risk factor for cardiovascular disease. First, there is no significant parasympathetic regulation of blood pressure. Only a limited number of blood vessels are affected by parasympathetic input, so nicotine will preferentially cause the vascular tone to become more sympathetic, which means blood pressure will be increased. Second, the autonomic control of the heart is special. Unlike skeletal or smooth muscles, cardiac muscle is intrinsically active, meaning that it generates its own action potentials. The autonomic system does not cause the heart to beat, it just speeds it up (sympathetic) or slows it down (parasympathetic). The mechanisms for this are not mutually exclusive, so the heart receives conflicting signals, and the rhythm of the heart can be affected ( [link] ).

Questions & Answers

what is oesophagus?
Bhavani Reply
oesophagus also known as food pip
ABDULLAH
What is the meaning of dissection
Beryl Reply
what's the meaning of polar?
Jackson Reply
Sign of anaemia or whitish color or Hgb luck
Kassahn
Are you talking of Polar anaemia or what, because the word polar doesnt have one meaning
Kingsley
what are the three types of adrenocorticoids hormones
Lubega Reply
glucocorticoids mineralocorticoid and catecholamines
Kartik
what is polar and non-polar
Jackson Reply
polar unequal share of electron while non polar is equal share
Quran
why are phosphate molecules negatively charged?
Jackson Reply
Bocz of unpaired elections
Javid
because of unpaired electrons
ABDULLAH
what are amphipathic molecules?
Jackson Reply
Amphipathic molecules are molecules with both polar and non polar regions
Mohammed
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MADUBULA Reply
Hw does the male organ develop
MADUBULA
Review your questions madam
Aliyu
what is anaphylaxis?
Rugut Reply
it is an imagency condition resulting from abnormal and immediate alagic response to a substance to which the body has become intensively sensitized
Lubega
different between drug and medicine
ado Reply
drugs have no medical application (cocaine, heroin, crystal meth). medicine have medical purpose (fentanyl, albuterol, aspirin, ect ect)
Jordan
medicine is a substance or preparation used in treating disease,drug is chemical compound medicine are drugs but all drugs are not medicines
Wafa
assalam o alaikum
Sidra
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Zwanga Reply
what are the smooth muscles of the heart
Sintung Reply
stomach
Sidra
identify external features of kidney
saba Reply
kidney weight on males?
saba
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saba
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Samim
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Samim
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saba
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saba
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saba
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saba
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saba
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Shahab
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saba
Define cranial nerves with oder
Javid
O-olfactory O-optic O-occumulator T-trochlear T-trigemenal A-abducent F-facial A-auditory G-glossopharyngeal V-vagus A-acessory
Aniee
opd mean?
Shahab
out patient department
mahesh
thnxx
Shahab
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Javid
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Areeej
Read KD Tripathi book of Pharmacology.
mayank
Hello
mayank
CT Scan means
Sintung
what's health?
Sintung
hello
Philip
hi
Sintung
CT means - computerized tomography
Vivek
connective tissue
Dee
they link some body organs
Sintung
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Javid
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saba
what is tomography?
Gideon
tomography ☝
shahid
yes
Gideon
how hemolytic anemia cause due to gas gangrene?
Huma Reply
what's gangrene?
Sidra
why retro abdominal region called or named "flank "?
Huma Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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