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The Autonomic Nervous System · Chapter 3 of 7
2005–2010, ages 30–35. Heartburn all through graduate school, a clean endoscopy, and the word “stress” on the report. A mouthThe opening of the digestive tract where food enters and mastication begins. that dries at a desk, a stomach that will not settle, a bladderA muscular organ that stores urine before excretion. that — after 2016 — will not empty. Every one of those is the division that is supposed to be in charge: the parasympathetic, craniosacral, carried mostly by one nerve, synapsing in the organ wall, speaking one chemical into two kinds of lock.
The question you will answer
The parasympathetic divisionPart of the autonomic nervous system that conserves energy and promotes rest-and-digest functions. runs most of a normal day. Before you can ask whether Stina’s brake still answers, you need where it leaves — four cranial nervesNerves that arise from the brain and control head and neck functions. and three sacral segmentsThe subdivisions of lung lobes, supplied by tertiary bronchi. — the vagus that carries most of it, the terminal ganglia that make it local, and the two receptorA structure that detects stimuli. families, nicotinic and muscarinic, that let acetylcholinealso know as ACh A neurotransmitter that stimulates muscle contraction. slow a heart and stimulate a gut with the same molecule.
Opener · The Vagus Highway · about 1¾ minutes
The opener is the same narrated animation you will watch in Scene 1.
Watch the opener first. It sets the question; the chapter answers it.
1
Read the chart
Patient chart · Stina
2005–2016 · ages 30–41 · the brake
2005–10 · 30–35
Heartburn all through grad school; clean endoscopy; “stress.” A cash chiropractor for the back; no insurance.
2006 · 31
Hospital for vomiting she can’t stop → “flu and dehydration” (no flu test).
2010–16 · 35–41
Dry mouth in flares; the heavy shut-down days after.
2016 · 41
Flaccid neurogenic bladder: the sacral loop that empties the bladder no longer answers (Spinal Cord, 9.5).
Standing
“Stress” sits beside the gut, the mouth and the bladder on three different pages.
Chart clues this module: #11 — An autopilot that tracks her markers
Before you go on · your prediction
A stomach that will not settle, a mouth that dries, a bladder that will not empty. The best first reading is…
Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.
Stress — the clean endoscopy says the organ is fine, so the problem is upstream in her head
Ask which nerve carries most of the parasympathetic supply to the stomach, where it synapses, and what “the organ is fine” does and does not rule out.
Three organs, three problems, three separate pages
Ask what the stomach, the salivary glands and the bladder wall have in common on the parasympathetic map.
The division in charge of rest has been losing arguments
Ask what it means for the parasympathetic to be “in charge mostly,” and what happens to its organs when the other division is turned up in the wrong hours.
From Stina’s diary
2
The story
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 · Stress, again
Graduate school was five years of heartburn. She could afford a cash chiropractor for her back and not much else, so the stomach went uninvestigated until an endoscopy, which came back clean, and the report said what reports said about her: <em>stress</em>. In 2006 a hospital kept her overnight for vomiting she could not stop and sent her home with “flu and dehydration” and no flu test. By her late thirties the list had a dry mouth on it too, the kind that stops words at a desk, and after 2016 a bladder that would not empty on its own. A stomach, a salivary gland, a bladder wall. Three pages, three specialties, and one word — stress — sitting beside each of them. What the three have in common is not stress. It is the division of the autonomic system that is supposed to be running them for most of every day, and the one nerve that carries most of it.
See it move: Scene 1 · Stress, Again
II · Craniosacral, and mostly the vagus
The parasympathetic division is <strong>rest and digest</strong>, <strong>craniosacral</strong>, and — the lecture notes underline it — <em>always in charge</em>, or in charge mostly: it is the division running your life between emergencies. It leaves the central nervous systemComposed of the brain and spinal cord; integrates and processes information. at two ends and nowhere in between. From the brainstemThe lower part of the brain that connects to the spinal cord and controls vital functions. it rides four cranial nerves: the <strong>oculomotor</strong> (III) to the pupil and lens, the <strong>facial</strong> (VII) to the tear and salivary glands, the <strong>glossopharyngeal</strong> (IX) to the parotid, and the <strong>vagus</strong> (X), which carries roughly nine-tenths of all parasympathetic outflow and wanders — the name means it — to the heart, the lungs, the stomach, the pancreasA gland that produces digestive enzymes and hormones like insulin and glucagon., the liverA large organ that produces bile, detoxifies blood, and stores nutrients., the small intestine and the first half of the large. From the sacral cord, <strong>S2 to S4</strong>, the pelvic nerves reach the rest of the colon, the bladder and the genitalia. Its preganglionic fibers are long and lightly myelinated; they synapseThe junction between two neurons where communication occurs. in <strong>terminal ganglia</strong> on or inside the wall of the organ, and the postganglionic fibers are short and unmyelinated. Both synapses use <strong>acetylcholine</strong>: always ACh at the ganglionA cluster of neuron cell bodies located in the peripheral nervous system (PNS)., and ACh again at the organ. That is why the lecture notes writes “ACh only” beside this division and colors it purple.
See it move: Scene 2 · Four Nerves and Three Segments · Scene 3 · Ganglia in the Wall
III · One chemical, two locks
If both synapses use the same molecule, how does a single chemical slow a heart and speed a gut? Because the receptor decides. The lecture notes list two kinds of cholinergic receptor. <strong>Nicotinic</strong> receptorsProteins located on the surface or inside cells that bind specific molecules (e.g., neurotransmitter — named because nicotine mimics ACh there — always receive ACh and are always stimulated; they sit on <em>all</em> postganglionic neuronsThe functional cells of the nervous system that transmit signals. (both divisions) and on the sarcolemma at the neuromuscular junctionThe connection between a motor neuron and a muscle fiber., which is a somatic site and worth saying so you do not file it under the ANS. <strong>Muscarinic</strong> receptors — named for a mushroom poison that mimics ACh there — sit on all the parasympathetic target organsOrgans affected by specific hormones., and they can <em>inhibit</em> (cardiac cellsThe basic structural and functional units of life. slow) or <em>stimulate</em> (the smooth muscle of the GI tract contracts, glands secrete) depending on which muscarinic subtype the organ installed. Same key, different locks. The parasympathetic effects fall out of the wiring: pupils constrict, the lens thickens for near work, tears and saliva flow, the heart slows, the bronchiolesSmall airways branching from the bronchi that lead to alveoli; lack cartilage and control airflow wi narrow, the stomach and intestine churn and secrete, the bladder’s detrusor contracts and its internal sphincter opens. And the exceptions, again: <strong>arrector pili and sweat glands have no parasympathetic receptors at all</strong>. A division that is local by construction — one ganglion per organ — and in charge by default, which means that when it is not, you notice one organ at a time and never the pattern.
See it move: Scene 4 · Nicotinic and Muscarinic · Scene 5 · The Organs That Cannot Hear It
3
Watch · explore · think · check
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.
How to read the scenes
- Animation (dark teal) — a short animated explainer, one idea each
- Slide (dark teal) — a still to study: a micrograph, a diagram or a map
- Explore (purple) — something to push on while you watch
- Game (purple) — a quick challenge
- Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
- Check (gold) — a quick H5P that scores itself
Scene 1 of 5
Stress, Again
A clean endoscopy, a word on a report, and three organs that share one division.
Animation · in production · 1 min 50 s
The Vagus Highway
The vagus leaving the medulla with its exits; the sacral road; the clock at rest; the heart at 70 under its brake. Caption: in charge mostly, and carried mostly by one nerve.
Prefer the full lecture? Parasympathetic Nervous System (original video on the site)
Explore · in production
What “clean” rules out
An endoscopy report — “mucosaThe innermost lining of the digestive tract that contains mucus-secreting cells for protection and a normal, no ulcer, no erosions” — beside a list of eight possible causes of heartburn and nausea (an ulcer, reflux, a motility problem, a sphincter that will not hold, an infection, an inflamed peritoneumThe membrane lining the abdominal cavity and organs., a drug, “stress”). Before any key, mark each as <em>ruled out by a clean scope</em>, <em>not addressed by a scope</em>, or <em>not a cause but a label</em>. Then a routing round: trace the nerve supply to the stomach wall from brainstem to gland, naming the nerve and the ganglion position. The reveal: what an endoscope can see, what it cannot, and where the vagus was the whole time.
Think · not graded
“Stress” was written beside her stomach, her mouth and later her bladder on three different pages. If stress is a real thing that genuinely changes autonomic output, what would you have to show to tell stress apart from a disease moving the same dials — and did anyone look?
The true/false spot-check for this prompt is in production.
Check · Drag the Words
Drag each term into the description of the parasympathetic wiring plan.
This self-scoring check is in production.
Evidence card 1
Add it to your evidence board
Stomach, salivary gland and bladder wall are all parasympathetic targets, each with its own ganglion — a division that shows trouble one organ at a time, on one page at a time.
Scene 2 of 5
Four Nerves and Three Segments
III, VII, IX, X and S2–S4 — and the one nerve that wanders.
Animation · in production · 1 min 45 s
Where the Brake Leaves
A brainstem in sagittal view with four nucleiClusters of neurons in the CNS responsible for processing information. lighting in order: III (a pupil narrows, a lens thickens), VII (a tear forms, saliva beads), IX (the parotid), X (the vagus, drawn as a trunk line down through the neckNarrow region just below the head; common fracture site. and thorax into the abdomen, exits lighting as it passes). Then the sacral cord: S2–S4 send the pelvic nerves to the descending colon, the bladder and the genitalia. A tally bar: the vagus carries about 90% of the traffic. Caption: four doors above, one below, and most of it through one nerve.
Prefer the full lecture? Parasympathetic Nervous System (original video on the site)
Explore · in production
Which door?
Ten effects appear one at a time — the pupil narrows; the lens rounds for reading; tears flow; the parotid salivates; the heart slows; the bronchioles tighten; the stomach churns; the pancreas secretes; the colon’s last third moves; the bladder empties. For each, before any key, pick the door: III, VII, IX, X or S2–S4. Then a harder pass: a lesion knocks out one door at a time — predict which effects vanish together. The reveal shows why damage to the vagus looks like many diseases and damage to S2–S4 looks like one.
Think · not graded
The sacral loop that empties Stina’s bladder stopped answering after the 2015 disc surgery. The vagus was never touched. What does that predict about her heart, stomach and colon — and does the chart agree?
The true/false spot-check for this prompt is in production.
Check · Mark the Words
Mark every structure the vagus reaches with parasympathetic fibers. Leave the others unmarked.
This self-scoring check is in production.
Evidence card 2
Add it to your evidence board
Her sacral door closed in 2016 and the bladder went quiet; the vagus door never did — so a stomach that would not settle was not a missing nerve but a nerve being argued with.
Scene 3 of 5
Ganglia in the Wall
Long then short, synapse in the organ — why the brake is local by construction.
Slide · in production
Terminal Ganglia
A parasympathetic chain with the ganglion drawn inside the organ wall beside a sympathetic chain with its ganglion beside the spineProminent ridge on the posterior scapula dividing it into supraspinous and infraspinous fossae., both labeled pre, ganglion, post.
Prefer the full lecture? Parasympathetic Nervous System (original video on the site)
Explore · in production
Build the brake
A cord, a brainstem, a bladder, a stomach and a heart, with loose parts: long axons, short axons, myelin wraps, ganglia, ACh chips. Build a parasympathetic chain to each organ — before any key — placing the ganglion, choosing the fiber lengths and wrapping myelin where it belongs. Then press “scare” and “meal” in turn: the reveal shows how many organs each chain can reach and why the parasympathetic never broadcasts.
Think · not graded
The lecture notes say a parasympathetic fiber “extends to the organ” and synapses there. If every parasympathetic ganglion serves exactly one organ, what would a parasympathetic disease look like compared with a sympathetic one — and which of the two would be easier to mistake for several unrelated problems?
The true/false spot-check for this prompt is in production.
Check · Flip Cards
Predict each answer, then flip.
This self-scoring check is in production.
Evidence card 3
Add it to your evidence board
One ganglion, one organ: the brake cannot fail everywhere at once the way the gas can surge everywhere at once — so a brake that is losing arguments looks like three separate complaints.
Scene 4 of 5
Nicotinic and Muscarinic
Two locks for one key — and the reason the same molecule slows a heart and speeds a gut.
Animation · in production · 2 min 00 s
Same Key, Two Locks
An ACh molecule as a key. Lock one, nicotinic: on every postganglionic cell bodyThe central part of a neuron containing the nucleus and organelles. (both divisions, green and purple) and on a skeletal-muscle sarcolemma; the key turns and the cell fires — always. Lock two, muscarinic: on a heart cell, the key turns and the beat slows; on a gut smooth-muscle cell, the key turns and the wall contracts; on a gland, secretionThe process of moving substances from the blood into the nephron tubule to be excreted in urine. beads. A mushroom and a tobacco leaf label the two names. Caption: the chemical does not decide; the receptor does.
Prefer the full lecture? ANS Neurotransmitters and Receptors (original video on the site)
Explore · in production
Which lock?
Nine sites on a body map — a sympathetic ganglion, a parasympathetic ganglion, the neuromuscular junction of the biceps, the SA node, the stomach wall, a salivary gland, the detrusor, the iris sphincter, a sweat gland. Drop a nicotinic or a muscarinic lock on each before any key, then predict the response to ACh at each: fire, slow, contract, secrete, or <em>no receptor here</em>. The reveal counts how many of the nine are the same molecule doing opposite things, and flags the two traps (the NMJ is somatic; the sweat gland’s muscarinic receptor is sympathetic).
Think · not graded
Nicotine mimics ACh at nicotinic receptorsCholinergic receptors found on postganglionic neurons and skeletal muscle; they respond to acetylcho and muscarine, a mushroom poison, mimics it at muscarinic ones. From the locations of the two receptor families alone, predict what a cigarette does to the autonomic system and what a bad mushroom does — and which of the two could a drug block without touching the other.
The true/false spot-check for this prompt is in production.
Check · Multiple Choice
Nicotinic receptors are always excitatory while muscarinic receptorsCholinergic receptors found on the effector organs of the parasympathetic nervous system; they media can excite or inhibit. What accounts for that difference?
This self-scoring check is in production.
Evidence card 4
Add it to your evidence board
The chemistry of the brake is one molecule and two locks — so a drug that blocks the muscarinic lock dries the mouth and stalls the gut and the bladder at once, and a disease that disturbs the key does the same.
Scene 5 of 5
The Organs That Cannot Hear It
Arrector pili and sweat glands — no parasympathetic receptors at all — and what that does to a patient who sweats on fever nights.
Animation · in production · 1 min 35 s
No Brake Here
A patch of skinThe body’s largest organ, providing protection and regulation.: a hair stands up (arrector pili), a sweat gland beads, an arteriole squeezes. A purple parasympathetic fiber arrives and finds no receptor — it bounces. A green sympathetic fiber arrives and everything responds. A dial labeled “sympathetic traffic” turns up and down; the hair, the sweat and the vessel follow it alone. Then a fever night: the dial goes up (chills, white hands), then down (the sweat pours). Caption: one rope, and only one hand on it.
Prefer the full lecture? Parasympathetic Nervous System (original video on the site)
Explore · in production
Pull the one rope
A skin block with a hair, a sweat gland and an arteriole, and two ropes — one green, one purple. Try the purple rope on each target before any key (nothing happens, and the page asks you why before it tells you). Then set the green rope to five levels and predict hair, sweat and vessel at each. Last: a fever-night timeline with the set-point rising and falling — drag the green rope along it and watch the chills and the sweat appear in the right order.
Think · not graded
On a fever night she goes white and shivers, then soaks the sheets. If sweat glands and skin vessels only hear the sympathetic divisionPart of the autonomic nervous system that prepares the body for stress and activity., what is the hypothalamusA small but vital brain region controlling hormones, temperature, and autonomic functions. actually ordering in each phase — and why does “rest and digest” have nothing to say about either?
The true/false spot-check for this prompt is in production.
Check · Multiple Choice
Which pair of targets has no parasympathetic receptors at all?
This self-scoring check is in production.
Evidence card 5
Add it to your evidence board
Her chills and her night sweats are the sympathetic division executing the hypothalamus’s fever order on targets that have no brake; nothing in rest-and-digest can stop either.
4
Your evidence board
Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: A division in charge by default, being argued with, Neither on its own, or Stress, or three unrelated organs. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.
Evidence board · drag and drop · in production
The sorting board for this chapter’s cards is being built. Until it arrives, sort your evidence cards on paper into the three columns above.
5
Your verdict
Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.
Look back at your prediction
A stomach that will not settle, a mouth that dries, a bladder that will not empty — the reading that fits best is…
Find the one you chose at the top. Does the evidence support it, refute it, or revise it?
- Stress — the clean endoscopy says the organ is fine, so the problem is upstream in her headRounded proximal end that fits into the acetabulum of the hip bone.
- Three organs, three problems, three separate pages
- The division in charge of rest has been losing arguments
Build your verdict · no writing
Choose the statement that holds in each set. The ones you keep become your argument.
This activity is in production.
6
The finding
Finding · the brake
In Charge Mostly
2005–2016: heartburn with a clean scope, vomiting called flu, a dry mouth, and after 2016 a bladder with its sacral loop gone. Chart entry: the parasympathetic division is craniosacral, carried mostly by the vagus, local by construction (one ganglion per organ), ACh at both synapses, and the receptor — nicotinic or muscarinic — decides the sign. Held open: whether a brake that still works can lose every argument.
Next · Chapter 4
Fight or Flight
The division that floors her: thoracolumbar outflow, a chain of ganglia beside the spine, two little bridges called rami, and three roads out of the trunk that let one fiber reach a pupil and a kidney.
Reliable information on rare diseases
NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation
Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.
Hop to:
← Familial Mediterranean Fever — case home
All pages for Module 11 — The Autonomic Nervous System
11.0 Module Overview
11.1 Things That Were Not Anxiety
11.2 Two Pedals
11.3 Rest and Digest
11.4 Fight or Flight
11.5 Two Chemicals, Four Locks
11.6 The Resting Hum
11.7 The Autopilot That Tracks Her Markers
11.8 Conclusion and Assessment
11.9 Evidence Behind the Case
All Modules
- Anatomical Language, Membranes & Homeostasis
- Just Enough Chemistry
- The Cell & Its Transport
- Making Cells & Proteins
- The Integumentary System
- The Skeletal System
- The Muscular System
- Nervous Tissue & the Senses
- The Spinal Cord
- The Brain & the Blood–Brain Barrier
- The Autonomic Nervous System
- Special Senses (in developmentThe process of growth and differentiation.)
- The Endocrine System
- Blood
- The Heart
- Blood Vessels
- The Digestive System
- The Respiratory System
- The Urinary System
- Fluids, Electrolytes & Acid–Base Balance
- The Reproductive System
- The Immune System
List of terms
- mouth
- bladder
- parasympathetic division
- cranial nerves
- segments
- receptor
- acetylcholine
- anatomy
- physiology
- central nervous system
- brainstem
- pancreas
- liver
- synapse
- ganglion
- receptors
- neurons
- neuromuscular junction
- target organs
- cells
- bronchioles
- mucosa
- peritoneum
- nuclei
- neck
- spine
- cell body
- secretion
- nicotinic receptors
- muscarinic receptors
- skin
- sympathetic division
- hypothalamus
- head
- development