Time To Read
Date Last Modified
The Muscular System · Chapter 1 of 7
1988, age 13, the year of the twenty-pound backpack: a fitness-test mile finished last, calves on fire for three days, and every fever bringing a deepAway from the surface of the body. whole-body ache with days hollowed out after. The nurse writes “deconditioned”. This chapter opens the chart, builds muscle as a tissue — four characteristics, five jobs, three types, a fiber’s vocabulary — and puts all three tissues on a slide before asking what “out of shape” would look like.
The question you will answer
Three kinds of muscle contract in three ways. Before you can say whether a thirteen-year-old who aches after every fever is out of shape, you need to know what muscle is, what it is for, and what each type looks like under a lens.
Opener · The Mile · 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
1988 · age 13 · the fitness test, the backpack, and the fevers
Gym
Fitness-test mile: last to finish; calves “on fire” for three days; soaked and shaking. Nurse’s note: “deconditioned — recommend a conditioning program”.
Fevers
Three or four a season, each with a deep ache in thighs, back and shoulders “like the flu” and heavy legs; strength normal between. After each, three to five days “hollowed out”.
Exam
Pediatrician: strength 5/5 in every limb, reflexesAutomatic responses to stimuli. normal, joints fine. “Growing pains. She’ll outgrow it.” No labs.
Not drawn
Creatine kinase, aldolase, ESR — nothing to compare an attack day with a quiet one.
Told
“Out of shape.” “Growing pains.” “Try to be more active.” (Hindsight: CK normal on every draw since 2016; ESR never.)
Chart clues this module: 1 · this chapter
Before you go on · your prediction
A thirteen-year-old whose muscles ache for days after every fever and burn after a mile, with full strength in the office and no labs. 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.
Deconditioning — she is out of shape, and an aching muscle after effort is what out-of-shape muscle does
Ask what deconditioning actually changes in a fiber (Chapter 5 will say) and whether it explains an ache that arrives with a fever on a day she did nothing.
Growing pains — a normal, harmless childhood ache that comes and goes
Ask whether growing pains come with a temperature, settle into the back and shoulders, and leave a person hollowed out for days — and what an honest clinician would have measured.
An inflamed body spending muscle for fuel — the same fire the earlier modules tracked, now read in the tissue that costs the most to run
Ask what a fever costs a muscle, which signals break muscle protein down, and why a tissue can hurt and be weak in an exam that finds full strength.
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 · Last across the line
In 1988 she was thirteen, in a new town with a clinic forty minutes away and a twenty-pound backpack. Her feet, shins, back and legs hurt most days; the floors were concrete. That spring the class ran the fitness-test mile and she finished last, soaked and shaking, with calves that burned for three days. The nurse wrote deconditioned. What nobody lined up was the other thing: three or four times a season a fever arrived, and with it a deep ache in her thighs, back and shoulders — like the flu, except nothing ever grew on a test — and her legs went heavy, as if she were walking through waterThe universal solvent essential for life.. When the fever broke she was hollowed out for days. In the office her strength was five out of five: growing pains. No one drew a creatine kinaseAn enzyme that helps transfer energy for muscle contraction. on an attack day to see whether muscle was breaking, or a sedimentation rate to see whether the body was on fire. Muscle is the tissue that costs the most to run, and hers was being charged for something.
See it move: Scene 1 · The Mile · Scene 5 · Three Slides at 40×
II · Four characteristics, five jobs, three tissues
Muscle is one of the four tissues, and what sets it apart is that it contracts: proteinsLarge molecules made of amino acids with various functions in the body. inside the cell pull against each other and make tension. The notes give it four special characteristics. Excitability — responsiveness, irritability — it answers an action potentialA rapid, temporary electrical charge that travels along neurons, allowing signal transmission.. Contractility — it shortens with force. Extensibility — it stretches without tearing. Elasticity — it recoils, as the detrusor does after the bladderA muscular organ that stores urine before excretion. empties. Five jobs follow: produce movementA fundamental property of life involving motion of the body or its parts.; maintain posture; stabilise joints; generate heat, which is what shivering is; and the odd jobs — arrector pili, the pupil, the sphincters at every entrance and exit. Three tissues do the work. Cardiac: involuntary, striated, branching cellsThe basic structural and functional units of life. joined by intercalated discs Structures in cardiac muscle that allow electrical connectivity.. Smooth: involuntary, not striated, spindle-shaped cells contracting as a sheet around hollow organs. Skeletal: voluntary, striated, a cylinder bundled with thousands of others into an organ on a bone — the bulk of this module, and the kind the Intro lecture says you must stop calling a cell. It is a fiber.
See it move: Scene 2 · Four Characteristics, Five Jobs · Scene 3 · Three Tissues, Three Shapes
III · A fiber’s vocabulary, and three slides at 40×
A skeletal fiber is one cell, born when hundreds of myoblasts fused — hence the many nucleiClusters of neurons in the CNS responsible for processing information. pushed to the edge, and the name. Everything inside gets a muscle name from sarco- (flesh) and myo- (muscle): the sarcolemma is the membrane; the sarcoplasm the cytoplasmThe gel-like substance within a cell that contains organelles and cytosol., laden with calcium, glycogenA storage form of glucose found in animals. and myoglobin; the sarcoplasmic reticulum a smooth ER rebuilt to store and release calcium; the myofibrils — cylinders of contractile protein filling over eighty percent of the fiber — carry the stripes. On the site’s slides at 40× the tissues separate. Slide 058: skeletal, long pink ribbons, flattened nuclei on the edge, faint striations. Slide 098-1: cardiac, branching cylinders, one central nucleusThe control center of the cell that contains DNA and directs cellular activities., dark step-like intercalated discs. Slide 155: smooth, pointed cells with cigar nuclei dead centre and no bands. That is the decision card. Hold her chart against it: if her muscle were out of shape, which of these would change — and would any of it hurt?
See it move: Scene 4 · The Vocabulary of a Fiber · Scene 5 · Three Slides at 40×
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
The Mile
A fitness test, a nurse’s note, and a fever every few weeks that nobody lined up.
Animation · in production · 1 min 40 s
The Mile
A track, a stopwatch, a girl crossing last; calves glowing for three days on a calendar; “deconditioned” typed on a nurse’s form. Then a fever thermometer, and the ache spreading on the figure — thighs, back, shoulders — legs drawn heavy; a calendar of hollowed-out days after. The pediatrician’s 5/5 strength grid; the empty lab column. Caption: the tissue that costs the most to run, charged for something.
Prefer the full lecture? Introduction to Muscular Tissue (original video on the site)
Explore · in production
Line up the year
Her 1988 on a timeline: fevers, the mile, the hollowed-out days, the two visits. Drag each complaint onto its day, then predict — before the overlay — which cluster with a fever and which with effort. Then the lab column: for each visit choose the one test you would have ordered and predict a quiet day against an attack day. Last: write the sentence the nurse should have written instead of “deconditioned”.
Think · not graded
A muscle can ache because it was overworked, because it is being broken down, or because the body is inflamed and every tissue is paying for the fever. Which of those three leaves strength at 5/5 in the office a week later — and which would a creatine kinase on an attack day have told apart?
The true/false spot-check for this prompt is in production.
Check · Single Choice
Which of the four special characteristics of muscle is the one that lets it answer a nerve?
This self-scoring check is in production.
Evidence card 1
Add it to your evidence board
Ache with every fever, days hollowed out after, full strength in the office, no labs drawn — a pattern that was filed as fitness.
Scene 2 of 5
Four Characteristics, Five Jobs
What muscle is for — including the jobs you never thought of.
Slide · in production
Four Characteristics, Five Jobs
The Intro lecture’s strange and wonderful functions: the pupil, the goosebumps — and shivering, which is muscle making heat on purpose.
Prefer the full lecture? Introduction to Muscular Tissue (original video on the site)
Game · in production
Which job, which characteristic?
Nine cards — a shiver, a goosebump, standing on a bus, a full bladder, a pupil in the dark, a swallow, a sprint start, a handstand, a fever — and two rows of bins. Sort each to the job it shows and to the characteristic it mostly uses, before the reveal. Then the fever card alone: predict which job a fever recruits and what it costs.
Think · not graded
Shivering is skeletal muscle making heat, and a fever is the body deciding to run hotter. If a thirteen-year-old shivers through a 39 °C evening, which job is her muscle doing, what is it burning to do it, and what should she feel like the next morning?
The true/false spot-check for this prompt is in production.
Check · Drag the Words
Match each example to the muscle function it shows.
This self-scoring check is in production.
Evidence card 2
Add it to your evidence board
Muscle makes heat on purpose — shivering — and a fever is a standing order for it.
Scene 3 of 5
Three Tissues, Three Shapes
Skeletal, cardiac, smooth — voluntary or not, striped or not, and three cell shapes you can draw.
Animation · in production · 1 min 40 s
Three Tissues, Three Shapes
A cylinder, a branched cylinder, a flame. Striped, striped, smooth. Voluntary, involuntary, involuntary. Skeletal attached to bone and bundled into organs; cardiac only in the myocardium, cells joined by intercalated discs; smooth in two sheets around every hollow organ — circular inside, longitudinal outside, the inchworm. Each shape then at 40× on the site’s slide. The lecture’s holiday-candle flame for the spindle.
Prefer the full lecture? Types of Muscle (original video on the site)
Game · in production
Shape, stripe, switch
Three unlabeled cells and three questions each — what shape, striated or not, voluntary or not — answered before the card flips. Then three organ cards (bicep, heart wall, small intestine) and three jobs (move a bone, pump as one, squeeze a tube), matched blind. Last: a histology field with no label; commit to a tissue, then say the one feature that decided it.
Think · not graded
Cardiac cells are joined by intercalated discs so the heart contracts as one; smooth cells share gap junctions so a sheet contracts together; skeletal fibers do neither and each needs its own nerve. What does that difference predict about which tissue you can train, which you can tire, and which one hurts when the whole body is inflamed?
The true/false spot-check for this prompt is in production.
Check · Drag the Words
Drop each muscle type beside its defining feature.
This self-scoring check is in production.
Evidence card 3
Add it to your evidence board
Three tissues that contract three ways — and the same inflammation reaches all three (Chapter 7).
Scene 4 of 5
The Vocabulary of a Fiber
Sarco- and myo-: the cell membrane, the cytoplasm, the reticulum and the cylinders inside the cylinder.
Slide · in production
A Fiber, Named
The lecture’s rule: always, always ask — fiber or myofibrilCylindrical structures within muscle fibers that contain myofilaments.? The fiber has many nuclei and striations; the myofibril shows actin and myosin with the reticulum wrapped around it.
Prefer the full lecture? The Muscle Fiber (original video on the site)
Explore · in production
Fiber or myofibril?
Eight pictures at eight scales, shuffled. For each, commit — whole muscle, fascicle, fiber, myofibril, or sarcomere — before the scale bar appears, and name the clue that told you (nuclei? striations? a reticulum? Z lines?). Then build the vocabulary: drag sarco- and myo- onto -lemma, -plasm, -plasmic reticulum, -fibril, -filament and predict what each names. Last: predict what fraction of a fiber is myofibril, then see the 80%.
Think · not graded
A fiber has many nuclei because myoblasts fused; it cannot divide, but satellite cells beside it can. If inflammation breaks muscle protein down for weeks, what can a fiber rebuild on its own, what needs the satellite cells — and why does none of that show up as “weakness” in a five-minute exam?
The true/false spot-check for this prompt is in production.
Check · Fill in the Blanks
Name the parts of a muscle fiber.
This self-scoring check is in production.
Evidence card 4
Add it to your evidence board
A fiber that cannot divide, repaired by satellite cells — a tissue that pays for damage slowly and quietly.
Scene 5 of 5
Three Slides at 40×
The decision card: ribbons with edge nuclei, branches with discs, spindles with central nuclei.
Slide · in production
Slides 058, 098-1 and 155
Amy’s own confession on the smooth page: when she cannot tell, she defaults to smooth muscle — “like choosing C”.
Prefer the full lecture? Types of Muscle (original video on the site) · histology page: Muscular Tissue Histology
Explore · in production
The decision card
The three slides with a stage you can drive. At 40×, before the overlay, mark the one feature that decides each tissue — edge nuclei, an intercalated disc, a cigar nucleus — and say whether the cut is cross or longitudinal (the chalk rule). Then three unknown fields, including the Journey’s trap (a cross-cut smooth sheet that looks like squamous epithelium): commit, then check for a lumenThe inside space of a hollow organ or structure.. Last: predict what an inflamed but not diseased skeletal muscle would look like on this slide.
Think · not graded
On slide 058 the nuclei sit at the edge; on 098-1 one nucleus sits in the centre; on 155 the nucleus is a cigar in the middle of a spindle. Why does skeletal muscle push its nuclei aside — what is taking the room — and what does that say about how much of a fiber is machinery?
The true/false spot-check for this prompt is in production.
Check · Image Hotspots
On the three site slides, find the striations, an intercalated disc, a peripheral nucleus, a central cigar nucleus and the endomysium.
This self-scoring check is in production.
Evidence card 5
Add it to your evidence board
Three tissues told apart by where the nucleus sits — a card that will be held against her chart in Chapter 7.
4
Your evidence board
Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: Inflammation spending muscle for fuel, Neither on its own, or Deconditioning, or growing pains. 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 thirteen-year-old whose muscles ache with every fever and burn after a mile, with full strength in the office — the reading that fits best is…
Find the one you chose at the top. Does the evidence support it, refute it, or revise it?
- Deconditioning — she is out of shape, and an aching muscle after effort is what out-of-shape muscle does
- Growing pains — a normal, harmless childhood ache that comes and goes
- An inflamed body spending muscle for fuel — the same fire the earlier modules tracked, now read in the tissue that costs the most to run
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 muscles were never out of shape
Last Across the Line
1988, age 13: a fitness-test mile finished last with three days of burning calves, filed as “deconditioned”; a deep whole-body muscle ache with every fever and days hollowed out after, filed as growing pains; strength 5/5 and no labs. Chart entry: muscle has four characteristics and five jobs, one of them making heat; a fever is a standing order for that job, and inflammation charges the most expensive tissue in the body for it. Nothing about these aches fits “out of shape” — the machinery, when examined, worked. What was never examined was the bill.
Next · Chapter 2
Built to Pull: Tendon to Sarcomere
Before we can read what inflammation costs a muscle, we build one — from the tendon that anchors it to the bone, through three connective-tissue wrappings, down one fiber, to the striped unit that actually shortens.
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 7 — The Muscular System
7.0 Module Overview
7.1 Muscles That Were Never Out of Shape
7.2 Built to Pull: Tendon to Sarcomere
7.3 The Signal: Nerve Meets Muscle
7.4 Calcium Turns the Key
7.5 The Fuel Bill
7.6 Grading the Pull
7.7 Three Muscles, One Fire
7.8 Conclusion and Assessment
7.9 The 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
- deep
- reflexes
- anatomy
- physiology
- water
- creatine kinase
- proteins
- action potential
- bladder
- movement
- cells
- intercalated discs
- nuclei
- cytoplasm
- glycogen
- nucleus
- myofibril
- lumen
- development