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Mydriasis

This photograph shows a person’s eye with a relatively large pupil.
The sympathetic system causes pupillary dilation when norepinephrine binds to an adrenergic receptor in the radial fibers of the iris smooth muscle. Phenylephrine mimics this action by binding to the same receptor when drops are applied onto the surface of the eye in a doctor’s office. (credit: Corey Theiss)

Other drugs that enhance adrenergic function are not associated with therapeutic uses, but affect the functions of the sympathetic system in a similar fashion. Cocaine primarily interferes with the uptake of dopamine at the synapse and can also increase adrenergic function. Caffeine is an antagonist to a different neurotransmitter receptor, called the adenosine receptor. Adenosine will suppress adrenergic activity, specifically the release of norepinephrine at synapses, so caffeine indirectly increases adrenergic activity. There is some evidence that caffeine can aid in the therapeutic use of drugs, perhaps by potentiating (increasing) sympathetic function, as is suggested by the inclusion of caffeine in over-the-counter analgesics such as Excedrin ® .

Sympatholytic drugs

Drugs that interfere with sympathetic function are referred to as sympatholytic, or sympathoplegic, drugs. They primarily work as an antagonist    to the adrenergic receptors. They block the ability of norepinephrine or epinephrine to bind to the receptors so that the effect is “cut” or “takes a blow,” to refer to the endings “-lytic” and “-plegic,” respectively. The various drugs of this class will be specific to α-adrenergic or β-adrenergic receptors, or to their receptor subtypes.

Possibly the most familiar type of sympatholytic drug are the β-blockers. These drugs are often used to treat cardiovascular disease because they block the β-receptors associated with vasoconstriction and cardioacceleration. By allowing blood vessels to dilate, or keeping heart rate from increasing, these drugs can improve cardiac function in a compromised system, such as for a person with congestive heart failure or who has previously suffered a heart attack. A couple of common versions of β-blockers are metoprolol, which specifically blocks the β 2 -receptor, and propanolol, which nonspecifically blocks β-receptors. There are other drugs that are α-blockers and can affect the sympathetic system in a similar way.

Other uses for sympatholytic drugs are as antianxiety medications. A common example of this is clonidine, which is an α-agonist. The sympathetic system is tied to anxiety to the point that the sympathetic response can be referred to as “fight, flight, or fright.” Clonidine is used for other treatments aside from hypertension and anxiety, including pain conditions and attention deficit hyperactivity disorder.

Parasympathetic effects

Drugs affecting parasympathetic functions can be classified into those that increase or decrease activity at postganglionic terminals. Parasympathetic postganglionic fibers release ACh, and the receptors on the targets are muscarinic receptors. There are several types of muscarinic receptors, M1–M5, but the drugs are not usually specific to the specific types. Parasympathetic drugs can be either muscarinic agonists or antagonists, or have indirect effects on the cholinergic system. Drugs that enhance cholinergic effects are called parasympathomimetic drugs    , whereas those that inhibit cholinergic effects are referred to as anticholinergic drugs    .

Questions & Answers

what are the layers of heart..?
Subhadatta Reply
epicardium , myocardium ,endocardium are three layers of heart
Antony
what is gestation
Antony
the period of development in mammals, from fertilisation of the ovum till birth
Paul
what's lactation?
Paul
secretion of milk from female breast
Antony
different between artery and veins?
Antony
ok
Paul
arteries caries oxygenated blood while veins caries deoxygenated blood except for pulmonary artery and pulmonary vein
Paul
can you guys HELP me with anatomy and physiology
Miriam
is this Mbbs first year course?
Zohaib
hi guys how are you today?
hingi Reply
fine and you
Bupe
good
Miriam
I would like to know that my self
Diana Reply
I need HELP
Miriam
can you guys help
Miriam
what do you need?
hingi
what help do you need
Onyeuku
and how should you be helped
Onyeuku
A _____ Propagation of the action potential. this is where the AP will travel down adjacent membranes on the neuron to transmit a message from one neuron to another. B. ______ K+ is the most prominent ion inside the cell and it is at resting membrane potential. C. _______ Repolarization occur;
Miriam
C. ______ Repolarization occur; allowing potassium ions to leak out of the cell changing the membrane permeability. D. ______ A stimulus changes the permeability of a patch of the membrane. this allow sodium ions to rush into the cell causing a change in the polarity of the membrane.
Miriam
E._____ the sodium- potassium pump pumps out sodium in potassium ions to restore the initial ionic conditions.
Miriam
is this course for first year Mbbs?
Zohaib Reply
yes...its for first year
Aftax
what does Mbbs means please?
Fatoumatta
what is clinical anatomy
Namweene Reply
study of clinical structures
Subhadatta
physiology of neurotransmission in ans
Pradip Reply
what about umbilical cord
Subhadatta Reply
nutrition passing tube
Antony
hi
Antony
it is a connection for transfer of hormones,blood,food,etc between child and mother during pregnancy.
Zohaib
yes..
Subhadatta
What the difference between anatomy and psychology
milika Reply
nothing
Sohil
hahaha Anatomy vs. Physiology. Students of anatomy learn about the structure of body parts, while those enrolled in physiologystudy the functions and relationships of body parts. While these two fields are often paired together in the same class or program title, they may also be offered separately.
Sohil
what is gross anatomy?
Vasco Reply
is the macroscopic form of anatomy where organs will be seen without the use of microscope
Kofi
yes
Aaliyah
yes
Memory
yes
godfrey
yes
Maddy
what is anatomy
Vasco Reply
is the structure of the part of the body
Kofi
when did we expect heat period
Kabiru Reply
when is pregnancy expected after ovulation
Kabiru
Minimum blood pressure
Hasnain Reply
120/80
AmirHameed
90/60
baila
120/80
Sri
were can anatomy work
capella Reply
in hospitality
Sri
what is normal flora
Cris Reply
it's one kind of bacteria
Tariq
the smallest blood vessel is capillary
Richard Reply
How does deoxygenated blood become oxygenated during blood circulation?
Richard
in lungs through alveoli ...
Subhadatta

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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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