Source: saved session 01a155db-c943-70ca-b8c8-2b2936783c63, October 19, 2026.
The original detailed write-up is preserved verbatim below. Desktop paths and verification claims refer to that original session, not this import. Educational material only; not a clinical protocol or medical device. Clinical statements, diagnostic thresholds, and treatment recommendations have not been independently verified during import. Original model assumptions and limitations are preserved; independent clinical review is required before teaching or patient-care use.
I read "tropin" as troponin. The interactive figure is built and works in both light and dark themes.
Files (in ~/Desktop/02_projects/anatomy-troponin/): troponin.html and troponin-light.html, built by build.mjs, plus preview-dark.png and preview-light.png.
The figure: a bench model of one heart-muscle filament
| Part of the machine | What it stands for |
|---|---|
| Row of beads on an axle, fixed to a plate on the left | Actin, anchored to the Z-disc |
| Thin rod on rocker links, lying across a white dot on each bead | Tropomyosin covering the myosin-binding sites |
| Collar clamped on the rod | TnT, which ties troponin to tropomyosin |
| Two-lobed dumbbell above the collar; the lobe with a cup is the one highlighted part | TnC; the cup is site II, the only regulatory calcium site in heart muscle |
| Arm running from the dumbbell down onto a bead | TnI, the latch that holds the system "off" |
| Reservoir overhead that drops a ball each beat | The sarcoplasmic reticulum releasing Ca²⁺ |
| Levers with ball heads in front of the beads | Myosin heads |
| Tray holding everything | The heart-muscle cell (membrane) |
| Spout and valve → vial with a tap → log scale with a red tick | Troponin leaking into blood, being cleared, and the 99th percentile cutoff |
| Loose pellets on the tray floor | The small free pool of troponin in the cell's cytoplasm |
Controls: on the left of the figure the heart is healthy and beating. Hover to the right to scroll through 0 h → 14 days after a coronary artery blockage. Click, or press Home, to go back to healthy. If you leave it alone, it plays a 30-second loop.
How troponin works
- At rest: TnI holds tropomyosin over the binding sites on actin, so myosin can't attach.
- Systole: Ca²⁺ goes from about 0.1 to about 1 µM and binds TnC's site II. TnC grabs TnI, TnI lets go of actin, and tropomyosin rolls off the sites. Myosin heads bind, pull, and the muscle shortens.
- Diastole: the SERCA pump takes Ca²⁺ back into storage. The ball rises back into the reservoir, tropomyosin rolls back, and the muscle relaxes.
Troponin is the calcium switch that turns each heartbeat on and off.
Why it is the test for a heart attack (MI)
Specific to heart: cardiac TnI is made only in heart muscle, and cardiac TnT almost only there. Older markers such as CK-MB also come from skeletal muscle.
It only gets out when cells die. In the model:
- Contraction stops within about a minute of the blockage.
- After about 30 minutes the damage can't be undone and the membrane fails (the valve opens).
- The small free pool in the cytoplasm leaks first: the pellets disappear.
- Then the much larger filament-bound pool leaks over days as the filaments break down.
Sensitive, and stays up a long time. In the model's moderate infarct, high-sensitivity troponin T (hs-cTnT):
Time after blockage hs-cTnT ~2 h passes 14 ng/L ~3 h ~50 ng/L 13 h 1,315 ng/L (first peak) day 3–4 second rise day 12 still above 14 ng/L The long tail lets you catch a heart attack days after it happened.
How it is used clinically: the Fourth Universal Definition of MI requires:
- a rise and/or fall in troponin,
- with at least one value above the 99th percentile of healthy people (14 ng/L for hs-cTnT),
- plus signs of ischaemia: symptoms, ECG changes, or imaging.
The ESC 0/1-hour hs-cTnT pathway:
- Rule out: below 5 ng/L at arrival (if chest pain began more than 3 h ago), or below 12 ng/L with less than a 3 ng/L rise at 1 h.
- Rule in: 52 ng/L or more at arrival, or a rise of 5 ng/L or more at 1 h.
Why the change over time matters: troponin also rises in myocarditis, pulmonary embolism, sepsis, heart failure and chronic kidney disease. One high value means heart injury; a rising-and-falling pattern plus a matching clinical picture means MI.
The curve's shape, timing and 14 ng/L cutoff follow published values. The calcium level and how strongly it switches the filament on are rounded textbook figures I tuned for teaching, so this is not for clinical use. The 99th-percentile cutoff depends on the assay, and is sex-specific for hs-cTnI.
Checks run:
- The line-end check found 0 loose line ends in both themes, and the browser console showed no errors.
- I captured and looked at the healthy beat (calcium in TnC, sites uncovered, heads bound), the blocked heart at 4 h, 7 h, 13 h, day 5 and day 14, a phone-width layout, and reduced motion.
- I didn't run the skill's geometry audit, which proves no parts collide. The figure has no pipes or cables (the case that audit covers), so I checked clearances by hand instead.