Muscle contraction: filaments slide
הוצג| English | משמעות |
|---|---|
| sarcomere/ˈsɑːkəmɪə/ | סרקומרה |
| cross-bridge/krɒs brɪdʒ/ | גשר צולב |
What would explain this observation?
- A sarcomere 肌节 becomes shorter during contraction although its thick and thin filaments keep approximately the same length.
Build the model
- Actin and myosin interact in a sliding-filament mechanism.
- Calcium permits the interaction through regulatory proteins; ATP binding and hydrolysis support the cross-bridge 横桥 cycle.
- Skeletal muscles pull through tendons and work in coordinated groups.
- sarcomere: The repeating contractile unit between two Z lines.
- cross-bridge: A myosin-actin interaction during the contraction cycle.
What happens to thick-filament length during normal contraction?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
In the sliding-filament model the filaments slide past each other: thick and thin filament lengths stay essentially constant while the sarcomere shortens. The overlap changes, not the filaments.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- During shortening, overlap increases.
- The A-band length stays approximately constant while I bands and the H zone become smaller.
- Movement at a joint also depends on tendon insertion, lever geometry and opposing muscle activity.
In the lab: Annotate two sarcomere diagrams at different lengths using the same scale. Track band widths separately from filament length. Use prepared models or existing images, not painful or maximal-exertion tasks.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: sarcomere length changes from 2.5 to 2.0 micrometres.
- Percentage shortening = (2.5 − 2.0)/2.5 × 100 = 20%.
- This does not mean either filament shortened by 20%.
Your turn: A sarcomere shortens from 3.0 to 2.4 micrometres. Calculate percentage shortening.
A sarcomere shortens from 3.0 to 2.4 micrometres. Calculate percentage shortening.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 20 %. Known: sarcomere shortens from 3.0 to 2.4 micrometres. Use percentage shortening = (initial - final) / initial x 100. Shortening = (3.0 - 2.4)/3.0 x 100 = 20%. The filaments themselves did not shrink by 20%.
Check the conclusion and its limits
- ATP is required for myosin detachment as well as the continuing cycle.
- A muscle pulling harder does not mean all its fibres become shorter under every load.
Not true: Contracting muscle shortens by shrinking every actin filament. Contraction is sliding, not shrinking: actin and myosin filaments keep their length while their overlap increases. A filament that shortened would contradict the sliding-filament evidence.
- Actin and myosin interact in a sliding-filament mechanism.
- During shortening, overlap increases.
- Watch for: ATP is required for myosin detachment as well as the continuing cycle.
Write from a shortening of 25 percent
- A sarcomere shortens from 2.0 to 1.5 micrometres.
- Find the percentage shortening. The filaments themselves do not shorten by that percentage.
Contracting muscle shortens by shrinking every actin filament.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Contraction is sliding, not shrinking: actin and myosin filaments keep their length while their overlap increases. A filament that shortened would contradict the sliding-filament evidence.
The repeating contractile unit between two Z lines: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
sarcomere means The repeating contractile unit between two Z lines.
A sarcomere shortens from 2.0 to 1.5 micrometres. What is the percentage shortening, and do the filaments themselves shorten by that percentage?
0.5 divided by 2.0 is 0.25, so the sarcomere shortening is 25 percent.
What is the percentage shortening of the sarcomere?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
0.5 divided by 2.0 is 25 percent, and the filament lengths stay about the same.