11.5 Two Chemicals, Four Locks

Three short movements: the case, the anatomyThe study of the structure of the human body. and physiologyThe study of how the body functions., then the tie back to Stina. Each links to the scene where you’ll see it move.

I · A month on a beta blocker

She filled the prescription because it was easier than arguing. A month of low-dose propranolol taught her more pharmacology than it fixed. The pulse ran softer; she could sit through a flare without hearing her heart in her ears. But her hands, already cold in flares, went colder. Mornings were gray and slow in a way that frightened her. Standing from a chair made the room tilt, and once, in a hallway, she had to sit on the floor. And the flares themselves — the fever, the pain, the pupils, the dry mouthThe opening of the digestive tract where food enters and mastication begins., the shut-down gut — arrived exactly as before, on exactly the same schedule. She stopped the drug and added the episode to the tally. What the month had actually shown was a clean experiment: block one receptor family and watch which symptoms go quiet, which get worse, and which carry on untouched. To read that experiment you need the two chemicals and the four locks.

See it move: Scene 1 · Block the Receiver

II · Two chemicals, four locks

Neurons that release acetylcholine are <strong>cholinergic</strong>; neuronsThe functional cells of the nervous system that transmit signals. that release norepinephrine are <strong>adrenergic</strong>. Every preganglionic fiberThe axon of a neuron that originates in the central nervous system and synapses in an autonomic gang in both divisions is cholinergic. Every parasympathetic postganglionic fiberThe axon of a neuron that originates in an autonomic ganglion and extends to a target organ or tissu is cholinergic. Most sympathetic postganglionic fibers are adrenergic — but the ones to the <strong>sweat glands</strong> are cholinergic, which is why your sweat glands answer to ACh on a muscarinic receptor even though the division driving them is sympathetic (the site calls the odd ones “paininthebutt neurons” and admits there is no better name). And release a transmitter where there is no receptor, as the site says, and “nothing happens.” The lecture notes sort the receptors into two families for the parasympathetic — <strong>cholinergic</strong>: nicotinic (all postganglionic neurons and the sarcolemma; always excited) and muscarinic (all target organsOrgans affected by specific hormones.; inhibit cardiac cellsThe basic structural and functional units of life., stimulate GI smooth muscle) — and adds a second family for the sympathetic: <strong>adrenergic</strong>, responding to NE and epinephrineadrenaline): Fight-or-flight hormone from the adrenal medulla., <strong>alpha</strong> and <strong>beta</strong>, “lots” of them. The subtypes make the pharmacology land. <strong>α1</strong> on vascular smooth muscle: constrict (vasomotor toneThe baseline level of vasoconstriction maintained by sympathetic nerve activity, allowing rapid adju, blood pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange.) — and on the bladder’s internal sphincter: hold. <strong>β1</strong> on the heart: faster and stronger — and on the kidney’s juxtaglomerular cellsCells that secrete renin in response to changes in blood pressure.: release reninAn enzyme secreted by the juxtaglomerular cells that helps regulate blood pressure by triggering the. <strong>β2</strong> on bronchiolar smooth muscle: relax — the airways open; on the liverA large organ that produces bile, detoxifies blood, and stores nutrients.: release glucoseA simple sugar that is the main source of energy for cells.. <strong>β3</strong> on the bladder wall: relax, so it can store. Alpha receptors are mostly excitatory; beta receptors are mostly inhibitory, with the heart as the loud exception. Now read the month. A <strong>beta blocker</strong> sits on the beta locks and stops NE binding: β1 blocked, the pulse softens; β2 blocked, nothing dilates the muscle vessels, the heart’s output falls, and in the skinThe body’s largest organ, providing protection and regulation. — which is α1 territory to begin with — the constriction wins unopposed: colder hands; the brainstem’s standing reflex loses its β1 heart response — the room tilts; and the fatigue is the price of a body that cannot be mobilized. What the drug did not touch: the hypothalamusA small but vital brain region controlling hormones, temperature, and autonomic functions. that was setting the fever, the cytokines that were setting the hypothalamus, and the sympathetic outflow itself, still firing at a receptor that no longer answered. She had blocked the receiver. Nobody had touched the sender.

See it move: Scene 2 · Which Lock, Which Sign · Scene 3 · The Drug Shelf

III · A gland wired like a nerve, and three jobs only this division does

Norepinephrine in a synapse has three fates: taken back up into the <em>postganglionic</em> terminal that released it and repackaged (you will see reuptakeThe reabsorption of neurotransmitters by the presynaptic neuron for reuse. drawn at the preganglionic neuron; it is the releasing terminal that takes it back), broken down by enzymesProteins that speed up chemical reactions in the body. — the glossary’s COMT outside the ending and MAO inside it — or carried off in the blood, where it circulates for a couple of minutes, finds any alpha or beta receptor it meets, and is finally degraded by the liver. That third fate is why sympathetic effects last <em>minutes</em> while parasympathetic ACh acts for <em>seconds</em>, and why NE can reach organs that have no sympathetic nerve at all. The <strong>adrenal medulla</strong> turns that leak into a design. It is a modified sympathetic ganglionA cluster of neuron cell bodies located in the peripheral nervous system (PNS).: preganglionic fibers from the lateral hornA part of the spinal cord’s gray matter, containing autonomic motor neurons. (roughly T5–T9, not the hypothalamus as the site says) travel in the greater splanchnic nerve through the celiac ganglion without synapsing and end on <strong>chromaffin cells</strong>, which have nicotinic receptorsCholinergic receptors found on postganglionic neurons and skeletal muscle; they respond to acetylcho like any postganglionic neuron and no axon at all — they release straight into the blood, about <strong>80% epinephrine and 20% norepinephrine</strong>, “really, really big and powerful postganglionic neurons.” The lecture notes’s list of what that blood-borne surge does: <em>mobilize fats, raise blood glucose, increase cell metabolism</em> — an <strong>adrenaline rush</strong> that prepares you for trauma, and the “sinking feeling in your stomach.” It is the third of the lecture notes’ <strong>unique roles of the sympathetic division</strong>, the jobs the parasympathetic has no equivalent for. The first is <strong>thermoregulation</strong>: skin vessels dilate to dump heat and constrict to conserve it, and the sweat glands fire — all one rope, all sympathetic, all taking orders from the hypothalamus, which is why a fever night runs white hands and chills on the way up and a soaked bed on the way down. The second is <strong>renin release</strong>: β1 receptors on the kidney’s juxtaglomerular cells answer sympathetic traffic by releasing renin, which raises blood pressure through angiotensin — relate it back to the beta blocker, which lowers pressure partly by switching that off; the Blood Vessels and Urinary modules take the loop the rest of the way. One correction to carry: the adrenal <em>cortex</em> is the other half of the gland and makes cortisol under the pituitary’s orders, not the sympathetic division’s — her flat cortisol rhythm at 38 belongs to the Endocrine module, not here.

See it move: Scene 4 · Three Jobs Only This Division Does · Scene 5 · A Gland Wired Like a Nerve

5 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.

Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: A sender upstream that no autonomic drug reaches, Neither on its own, or Anxiety treated correctly, or a drug that simply failed. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.

Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.