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Biology · 术语表

什么是 Skeletal muscle and tendon？

又称： skeletal muscle · tendon

Definition 9.4 High School Biology · 第 9 章 — Muscles and Joints

A skeletal muscle is an organ made of thousands of long cells, the muscle fibres, bundled together; each fibre shortens when stimulated by a nerve. At both ends the muscle narrows into a tendon, a cord of non-contractile tissue attached to bone. A muscle can only pull, by shortening, and only along its own length: it moves a joint by pulling on the bone beyond it.

The forearm as a lever: the biceps pulls close to the pivot, the load hangs far from it.

F_{\text{muscle}} \times d = F_{\text{load}} \times D

, so the muscle force is

D/d = 7

times the load.

示例

Example 9.7 (Holding a bag)

A $5\,\mathrm{kg}$ bag (weight $49\,\mathrm{N}$ ) hangs from the hand, $35\,\mathrm{cm}$ from the elbow; the biceps tendon attaches $5\,\mathrm{cm}$ from it. The biceps pulls with $49 \times 35/5 = 343\,\mathrm{N}$ — seven times the load, the weight of $35\,\mathrm{kg}$ — and the elbow joint is pressed together with about $300\,\mathrm{N}$ . Muscles, tendons and cartilage are built for these forces; what damages them is a sudden force in the wrong direction, or a load repeated beyond what the tissue can repair.

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