Autonomic Nervous System Pharmacology

Flashcards reviewing foundational concepts, receptor locations, organ responses, and clinical pharmacology for the Autonomic Nervous System.

What is autonomic tone?

Autonomic tone is the balance between the continuously running sympathetic and parasympathetic nervous system branches, where organ function reflects whichever tone is currently dominant.

What are the anatomical origin, fiber lengths, neurotransmitters, and overall goal of the sympathetic nervous system?

The sympathetic system originates in the thoracolumbar spinal cord (T1 to L2), has short preganglionic and long postganglionic fibers, uses norepinephrine on adrenergic receptors at target organs, and aims to move blood and oxygen to muscles, brain, and heart (summarized by the four E's: Exercise, Excitement, Emergency, Embarrassment).

What are the anatomical origin, fiber lengths, neurotransmitters, and overall goal of the parasympathetic nervous system?

The parasympathetic system originates in the craniosacral region (cranial nerves III, VII, IX, X and S2 to S4), has long preganglionic and short postganglionic fibers, uses acetylcholine on muscarinic receptors at target organs, and aims to conserve energy, digest food, and empty the bladder and bowel (summarized by the three D's: Digestion, Defecation, Diuresis).

Why do sympathetic responses affect the body diffusely while parasympathetic responses are targeted?

Sympathetic postganglionic fibers are long and widely branched, causing diffuse whole-body responses, whereas parasympathetic postganglionic fibers are short and far more targeted.

What effects do sympathetic and parasympathetic stimulation have on the heart?

Sympathetic stimulation increases heart rate and contractility, whereas parasympathetic stimulation decreases heart rate.

What effects do sympathetic and parasympathetic stimulation have on the bronchioles?

Sympathetic stimulation dilates bronchioles (more air moves in), whereas parasympathetic stimulation constricts bronchioles and increases secretions.

What effects do sympathetic and parasympathetic stimulation have on pupils?

Sympathetic stimulation causes pupil dilation (mydriasis), whereas parasympathetic stimulation causes pupil constriction (miosis).

What effects do sympathetic and parasympathetic stimulation have on the gastrointestinal tract?

Sympathetic stimulation decreases GI motility and secretions, whereas parasympathetic stimulation increases GI motility and secretions.

Which organs or tissues receive sympathetic input exclusively?

Sweat glands and most blood vessels.

What neurotransmitter and receptor type are present at all preganglionic autonomic ganglia?

Acetylcholine (ACh) acting on nicotinic receptors.

What neurotransmitter is released by sympathetic postganglionic fibers at sweat glands?

Acetylcholine (ACh) acting on muscarinic receptors, which is an exception to typical sympathetic signaling and explains why anticholinergic drugs stop sweating.

How does the adrenal medulla function within the sympathetic nervous system?

It functions as a modified ganglion directly stimulated by preganglionic fibers to release epinephrine into the bloodstream as a hormone.

Where are N-n and N-m nicotinic receptor subtypes located?

N-n (neuronal) receptors are located in all autonomic ganglia and the adrenal medulla. N-m (muscle) receptors are located at the neuromuscular junction of skeletal muscle.

What are the locations and primary functions of M1, M2, and M3 muscarinic receptors?

M1: CNS and gastric parietal cells (memory, cognition, acid secretion). M2: Heart (slows rate; vagus nerve braking system). M3: Smooth muscle and glands (bronchoconstriction, GI motility, bladder emptying, salivation, tearing, pupil constriction).

What physiological responses result from Alpha-1 receptor activation?

Vasoconstriction, blood pressure elevation, urinary retention, and pupil dilation.

What is the function of Alpha-2 adrenergic receptors?

Located on the presynaptic nerve terminal, Alpha-2 receptors act as a feedback brake to shut off further norepinephrine release, causing blood pressure to fall.

What are the primary locations and functions of Beta-1 adrenergic receptors?

Located in the heart and kidney (juxtaglomerular cells), Beta-1 activation increases heart rate and contractility and stimulates renin release.

What are the primary locations and functions of Beta-2 adrenergic receptors?

Located in bronchioles, uterus, skeletal muscle, and liver, Beta-2 activation causes bronchodilation, uterine relaxation, tremor, and glucose release.

What memory hook distinguishes Beta-1 from Beta-2 receptor locations?

"You have one heart and two lungs" — Beta-1 is cardiac and Beta-2 is pulmonary.

What does the SLUDGE mnemonic stand for regarding cholinergic agonist effects?

Salivation, Lacrimation, Urination, Defecation, GI cramping, Emesis (along with the dangerous three: bradycardia, bronchoconstriction, and hypotension).

What is bethanechol used for, and what is its antidote?

Bethanechol is given for non-obstructive urinary retention (after surgery or childbirth) to contract the detrusor muscle and relax the sphincter; its antidote is atropine.

What rhyming mnemonics describe anticholinergic side effects?

"Blind as a bat" (blurred vision, dilated pupils, worsened glaucoma), "Dry as a bone" (dry mouth, no sweating, urinary retention, constipation), "Red as a beet" (flushed skin), "Hot as a hare" (fever, heat-stroke risk), and "Mad as a hatter" (confusion, agitation, hallucinations).

What are the primary clinical indications for atropine, ipratropium, oxybutynin, and scopolamine?

Atropine raises heart rate in symptomatic bradycardia; ipratropium is inhaled to open airways in COPD; oxybutynin calms an overactive bladder; scopolamine is a patch for motion sickness.

Why is epinephrine the primary drug for anaphylaxis?

It acts on both Alpha and Beta receptors to simultaneously open airways and raise blood pressure.

What is the key administration precaution for IV Norepinephrine?

A central line is preferred because extravasation can cause tissue necrosis.

What is the IV vasopressor monitoring rule?

Assess the infusion site every hour; if blanching, coolness, or pain occurs, stop the infusion immediately and notify the provider.

What is the clinical difference between cardioselective and nonselective beta blockers?

Cardioselective beta blockers (metoprolol, atenolol) target Beta-1 receptors only and are safer in respiratory disease; nonselective beta blockers (propranolol) target Beta-1 and Beta-2 and can trigger bronchospasm.

What three critical warnings apply to beta blockers?

1. Never stop abruptly (taper over 1-2 weeks to prevent rebound tachycardia, severe hypertension, and MI). 2. Masks hypoglycemia (blunts tremor and racing heart). 3. Caution in asthma (nonselective agents block Beta-2).

Why should the first dose of an alpha blocker like prazosin be given at bedtime?

To prevent injury from first-dose syncope caused by a sudden drop in blood pressure.

What are the four steps of the ANS drug reasoning method?

Step 1: Which receptor? (Alpha, beta, muscarinic, nicotinic). Step 2: Where does it live? (Heart, lungs, vessels, bladder, eye, gut). Step 3: Agonist or blocker? (Turning on or shutting off). Step 4: So what happens? (Predict effect, side effect, and assessment).