Muscles and contraction
Introduced| English | Meaning |
|---|---|
| striated muscle/ˈstraɪeɪtɪd ˈmʌsl/ | Skeletal muscle with a striped appearance, made of fibres that contract voluntarily. |
| sliding filament model/ˈslaɪdɪŋ ˈfɪləmənt ˈmɒdl/ | The explanation of muscle contraction in which actin and myosin filaments slide past one another, shortening sarcomeres without shortening the filaments. |
| sarcomere/ˈsɑːkəmɪə/ | A repeating contractile unit of striated muscle between two neighbouring Z lines. |
| myosin/ˈmaɪəsɪn/ | myosin |
| actin/ˈæktɪn/ | actin |
| sarcoplasmic reticulum/ˌsɑːkəˈplæzmɪk reˈtɪkjʊləm/ | A specialised membrane system in muscle cells that stores and releases calcium ions involved in contraction. |
| troponin/ˈtrɒpənɪn/ | A regulatory protein complex on thin muscle filaments that binds calcium and helps expose myosin-binding sites on actin. |
| tropomyosin/ˈtrɒpəmɪɒsɪn/ | A protein lying along actin filaments that blocks myosin-binding sites when a muscle fibre is relaxed. |
How muscles contract
- Striated muscle 横纹肌 is made of long fibres.
- Inside, tiny filaments slide over each other to shorten the muscle.
- This is the sliding filament model 肌丝滑动模型.
Muscle structure
- Each fibre is divided into repeating units called sarcomeres 肌节.
- Inside are two filaments: thick myosin 肌球蛋白 and thin actin 肌动蛋白.
- The T-tubules carry the impulse deep into the fibre, and the sarcoplasmic reticulum 肌质网 stores and releases calcium ions.
The sliding filament model of muscle contraction
How a muscle contracts
Step through the sliding filament model — calcium uncovers the binding sites, then myosin pulls the actin inwards.
A sarcomere is:
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Muscle fibres are divided into sarcomeres, each holding thick (myosin) and thin (actin) filaments.
The calcium ions for contraction are stored in, and released from, the ______ reticulum.
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When the impulse arrives, the sarcoplasmic reticulum releases Ca²⁺ to trigger contraction.
The sliding filament model
- an impulse makes the sarcoplasmic reticulum release calcium ions.
- calcium binds troponin 肌钙蛋白, which moves tropomyosin 原肌球蛋白 to uncover the binding sites on actin.
- myosin heads attach to actin and pull it inwards, using energy from ATP.
- the thin filaments slide over the thick ones, so each sarcomere shortens — the muscle contracts.
Nervous control is fast and electrical; hormonal control is slow and chemical
Calcium ions cause contraction by:
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Calcium binds troponin; tropomyosin shifts to expose actin, so myosin heads can attach.
In the sliding filament model, a sarcomere shortens because:
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Myosin heads attach and pull actin inwards (powered by ATP), so the filaments slide and the sarcomere shortens.
Put muscle contraction in order.
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Impulse → Ca²⁺ released → sites uncovered → power stroke → sarcomere shortens.
Match each part to its role in contraction.
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Ca²⁺ exposes the sites, myosin pulls actin (the power stroke), and ATP both powers and releases the heads.
The role of calcium and ATP
- A nerve impulse releases calcium ions, which expose the binding sites on the actin.
- ATP powers the cross-bridges that pull the filaments past each other, then resets them.
You've got it
- striated muscle = fibres divided into sarcomeres (thick myosin + thin actin)
- T-tubules carry the impulse in; the sarcoplasmic reticulum releases calcium
- calcium binds troponin → moves tropomyosin → uncovers actin sites
- myosin heads pull actin (using ATP) → sarcomere shortens (sliding filament model)