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Autonomic Nervous System Pharmacology

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Like the dishwasher automatically washes your dishes, your brain automatically does things for you as well. Find out how this is so and how medications can influence the systems responsible.

What Is The Autonomic Nervous System?

While you are thinking about what to have for breakfast, how best to get to school, how to complete that important report for school, and when you'll see your friends tonight, your brain is actually doing a lot of things without your knowledge. When you're running, sleeping, walking, or talking, it does the same.

What does it do? It regulates important bodily functions without your conscious input, like breathing rate, heart rate, digestion, and blood pressure.

The brain does this thank to a proxy called the autonomic nervous system (ANS), the one that helps regulate your body's internal processes, like the ones just mentioned a second ago.

The drugs that affect the ANS are divided into two main sections. They are the cholinergic drugs and the adrenergic drugs. Some of these drugs are agonists, which means they bind and activate a receptor to produce a biological response. Others are antagonists, which bind to receptors and block normal responses. Let's cover the basics of the cholinergic drugs first.

Cholinergic Drugs

Cholinergic drugs are those that affect the receptors that are normally activated by a natural biochemical found in the body called acetylcholine (Ach). The cholinergic receptors are themselves divided into two main types. One is type is called the muscarinic receptor and the other is called the nicotinic receptor.

One cholinergic drug is bethanechol. This drug is a cholinergic agonist, meaning it stimulates muscarinic receptors. One of the consequences of this is the stimulation of a certain muscle in the bladder that contracts in order to expel urine. In cases where the bladder isn't contracting, bethanechol can be used to help a person urinate.

The flipside to a drug like bethanechol is a drug like atropine, which binds to the muscarinic receptor but doesn't stimulate it. It also blocks the ability of acetylcholine to bind and stimulate the receptors. That's why it's known as a cholinergic antagonist.

Atropine can be used for many functions but is most famous for dilating the pupil when applied topically to the eye. This helps your eye-doctor examine the inner depths of your eye while shining a light into your eye at the same time. Had atropine not been applied, the pupil would've constricted in the response to the light and the doctor would have had a hard time seeing inside!

Adrenergic Drugs

Adrenergic drugs are those that act on receptors normally stimulated by two biochemicals called epinephrine and norepinephrine. Drugs of the same name are often used in medicine.

Epinephrine is an adrenergic agonist, meaning it binds and stimulates adrenergic receptors. Epinephrine can be given for a wide variety of reasons. For example, epinephrine not only increases heart rate but also strengthens the contraction of the heart muscle.

Epinephrine may be used to restore a person's heart rhythm during cardiac arrest as a result. The administration of epinephrine also results in a powerful widening of the airways of the lungs (bronchodilation). Thus, it is a drug that can be used to counteract the life-threatening effects of a serious bronchospasm in people with a severe response to an allergen, like peanuts.

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