Autonomic Nervous System 2

Whats a good drug for asthma/emphysema? What should we avoid?

A B2 agonist to bronchodilate (albuterol) or an M3 blocker (Ipratropium). Avoid Beta blockers.

What drugs will help dilate the pupil, and how?

An M3 blocker (atropine) or an a1 agonist (phenylephrine).

Whats the difference between epinephrine and norepinephrine in the receptors they act on?

Epinephrine acts on all the adrenergic receptors; norepinephrine acts on the a1, a2, and B1.

Cardiac Output = ?

Heart Rate X Stroke Volume

Under which system's control in the blood pressure via the constriction of small resistant arterioles? Despite this, describe the contribution of M3 receptors in the vascular endothelium.

Small resistant arterioles are under the sympathetic control via a1 receptors. THERE IS NO PARASYMPATHETIC INNERVATION OF THESE VESSELS. However M3 receptors, when activated by acetylcholine, release Nitric Oxide which dilates the vessels. So a drug that stimulates the M3 receptors will dilate the vessels.

Why inject epinephrine together with drugs like local anesthetics?

So constrict vessels and keep the drugs acting locally.

Describe the innervation of the lungs.

Sympathetic innervation is sparse; however, the adrenal medulla's epinephrine can act on the many B2 receptors that ARE present in the lungs. When activated they cause bronchodilation. The lung is mostly innervated parasympathetically. There are M3 receptors that are activated by acetylcholine causing bronchoconstriction.

Describe how the adrenal medulla of the sympathetic systems increases heart rate. Where are the receptors?

The adrenal medulla, when stimulated, releases epinephrine which acts on receptors that are located primarily in the ventricles (unlike the sites of the muscarinic or B1 receptors!). This increases the stroke volume.

Describe the innervation of the bladder.

The bladder is both sympathetically and parasympathetically innervated. There are a1 receptors in the detrusor that cause relaxation when activated sympathetically, and there are B2 receptors in the sphincter that cause contraction when activated sympathetically. This decreases emptying of the bladder.

Describe the innervation of the eye.

The eye is innervated both sympathetically and parasympathetically. The radial (dilator) muscle of the eye has a1 receptors that are sympathetic; the circular (constrictor) muscle has M3 receptors that are parasympathetic.

Describe the sympathetic & parasympathetic innervation of the heart, and under which control it typically falls. Which nerve/nerve levels innervate the heart? What are the sites in the heart where the nerves act on muscarinic or B1 receptors?

The heart is innervated by both of course, but at rest it's primarily under parasympathetic control while when active or stressed it falls under sympathetic control. The vagus nerve provides the parasympathetic innervation of the heart; sympathetic is provided by nerves from levels T2-T4. The SA and AV nodes are the sites of action, so heart rate is increased.

Describe the innervation of the penis.

The penis is innervated parasympathetically via M3 receptors in the vessels that, when activated, cause vasodilation and erection. The sympathetic system also indirectly causes erection by increasing blood pressure.

Describe the innervation of the vas deferens.

The vas deferens has a1 receptors that, when stimulated sympathetically, cause contraction and ejaculation.

Describe the innervation of "mixed" vessels.

These are the vessels on the endothelium of the coronary & pial (brain) vessels. They are innervated by the sympathetic system and have a2 receptors that, when activated by NE or E, cause vasodilation. The result is more blood to the heart & brain.

What's a clinical use of epinephrine/norepinephrine? What is the problem in using these clinically?

They are sometimes used in surgery to support the blood pressure by acting on the heart (B1 receptors) and blood vessels. Epinephrine is used for anaphylactic shock, too, because severe allergic reactions cause vasodilation, bronchoconstriction, etc and epinephrine counteracts these effects. These are very nonspecific and so will tend to have a lot of unintended effects.

Describe the innervation of the lens of the eye.

This is innervated only by the parasympathetic system. The ciliary muscle has M3 receptors that when stimulated contract, allowing the lens to become more spherical.

Describe the innervation of larger blood vessels that supply skeletal muscle.

Trick question! They have no sympathetic or parasympathetic innervation. They DO have B2 receptors, however, which when stimulated by epinephrine cause vasodilation via a G protein coupled receptor.

What's a good drug to use for angina pectoris/MI?

Use a Beta blocker (propranolol, metroprolol) to block the effects of epinephrine on the beta receptors of the heart.