📚 Tendons, Muscles and Bones: Exam Practice | 肌腱、肌肉与骨骼：真题精练
Master the key concepts of locomotion and support in organisms by working through high‑yield exam‑style questions. This revision resource covers the microscopic structure of skeletal muscle, the sliding filament mechanism, the role of tendons and bones in movement, and common pitfalls seen in A‑level examinations. Use the paired English‑Chinese explanations to strengthen both your biological knowledge and your scientific vocabulary.
通过高命中率的真题式练习，掌握生物体运动与支撑的核心概念。本复习资源涵盖骨骼肌的显微结构、肌丝滑动机制、肌腱和骨骼在运动中的作用以及A‑level考试中的常见误区。借助中英双语对照讲解，同时巩固生物学知识和科学词汇。
1. Microanatomy of Skeletal Muscle | 骨骼肌显微解剖
A skeletal muscle is composed of bundles of muscle fibres, each fibre being a multinucleate cell containing many myofibrils. Myofibrils are built from repeating units called sarcomeres, which are the fundamental contractile units. The regular arrangement of actin (thin) and myosin (thick) filaments gives skeletal muscle its characteristic striated appearance under the microscope.
骨骼肌由肌束组成，每根肌纤维是一个多核细胞，内含大量肌原纤维。肌原纤维由称为肌节的基本收缩单位重复排列而成。肌动蛋白（细肌丝）和肌球蛋白（粗肌丝）的有规律排列使骨骼肌在显微镜下呈现出特征性的横纹外观。
- Sarcolemma – the plasma membrane of a muscle fibre. | 肌膜 – 肌纤维的质膜。
- Sarcoplasmic reticulum – specialised endoplasmic reticulum that stores and releases Ca²⁺. | 肌浆网 – 特化的内质网，储存并释放钙离子。
- T‑tubules – invaginations of the sarcolemma that propagate action potentials deep into the fibre. | T管 – 肌膜的内陷，将动作电位快速传至纤维深处。
2. The Sliding Filament Model | 肌丝滑动模型
The sliding filament theory describes how muscle contraction occurs by the actin and myosin filaments sliding past each other, causing the sarcomere to shorten. Myosin heads bind to actin forming cross‑bridges, then execute a power stroke that pulls the actin filaments toward the M‑line. ATP is required both for the release of myosin from actin and for the re‑cocking of the myosin head.
肌丝滑动学说描述了肌动蛋白丝与肌球蛋白丝相互滑过，导致肌节缩短的收缩过程。肌球蛋白头部与肌动蛋白结合形成横桥，随后完成动力冲程，将肌动蛋白丝拉向M线。ATP既是肌球蛋白从肌动蛋白上释放所必需的，也是肌球蛋白头部重新翘起所必需的。
Ca²⁺ binds troponin → tropomyosin moves → myosin‑binding sites exposed → cross‑bridge cycle runs
Ca²⁺与肌钙蛋白结合 → 原肌球蛋白移动 → 肌球蛋白结合位点暴露 → 横桥循环运行
3. Initiation of Contraction: Neuromuscular Junction | 收缩的启动：神经肌肉接头
An action potential arriving at the presynaptic terminal of a motor neurone triggers the fusion of synaptic vesicles with the membrane, releasing the neurotransmitter acetylcholine (ACh) into the synaptic cleft. ACh diffuses across and binds to nicotinic receptors on the sarcolemma, opening sodium ion channels. This depolarises the muscle fibre, initiating a new action potential that spreads along the sarcolemma and down the T‑tubules.
运动神经元突触前末梢到达的动作电位触发突触小泡与膜融合，将神经递质乙酰胆碱释入突触间隙。乙酰胆碱扩散至肌膜上的烟碱受体并与之结合，打开钠离子通道。这使肌纤维去极化，引发新的动作电位沿肌膜传播并深入T管。
| Structure | Function |
|---|---|
| Synaptic knob | Contains vesicles of ACh |
| Synaptic cleft | Narrow gap across which ACh diffuses |
| Motor end plate | Region of sarcolemma with ACh receptors |
Table: Key features of the neuromuscular junction. | 表：神经肌肉接头的关键特征。
4. Excitation–Contraction Coupling | 兴奋‑收缩耦联
Excitation–contraction coupling is the process by which an action potential in the sarcolemma triggers the release of Ca²⁺ from the terminal cisternae of the sarcoplasmic reticulum. The released Ca²⁺ ions flood the sarcoplasm, bind to troponin, and remove the tropomyosin block on actin, allowing myosin heads to attach and the cross‑bridge cycle to proceed. When stimulation ceases, Ca²⁺ is actively pumped back into the sarcoplasmic reticulum using ATP.
兴奋‑收缩耦联是指肌膜上的动作电位引发肌浆网终池释放Ca²⁺的过程。释放出的Ca²⁺离子涌进肌浆，与肌钙蛋白结合，解除原肌球蛋白对肌动蛋白的阻滞，使肌球蛋白头部得以附着，横桥循环随即进行。刺激停止后，Ca²⁺通过主动转运消耗ATP被泵回肌浆网。
- ATP is hydrolysed by Ca²⁺-ATPase pumps on the SR membrane. | 肌浆网膜上的Ca²⁺-ATP酶泵水解ATP。
- Rigor mortis occurs when ATP is depleted, so myosin heads cannot detach from actin. | 尸僵是由于ATP耗尽，肌球蛋白头部无法从肌动蛋白上解离而发生的。
5. Types of Skeletal Muscle Fibres | 骨骼肌纤维类型
Skeletal muscle fibres can be classified into slow oxidative (type I), fast oxidative‑glycolytic (type IIa), and fast glycolytic (type IIb) fibres. Slow‑twitch fibres have a rich capillary supply, high myoglobin content, and many mitochondria, making them fatigue‑resistant and suited for endurance activities. Fast glycolytic fibres rely mainly on glycolysis, store large amounts of glycogen, produce rapid bursts of power, but fatigue quickly.
骨骼肌纤维可分为慢缩氧化型（I型）、快缩氧化‑糖酵解型（IIa型）和快缩糖酵解型（IIb型）。慢缩纤维含有丰富的毛细血管、高浓度的肌红蛋白和大量线粒体，抗疲劳性强，适合耐力活动。快缩糖酵解纤维主要依靠糖酵解供能，储存大量糖原，能快速产生爆发力，但易疲劳。
Examiners often ask you to relate fibre type distribution to athletic performance, e.g., sprinters possess a higher proportion of fast‑twitch fibres, while marathon runners have more slow‑twitch fibres.
考官常要求将纤维类型分布与运动表现联系起来，例如短跑选手的快缩纤维比例较高，而马拉松选手拥有更多的慢缩纤维。
6. Gross Anatomy of a Long Bone | 长骨的大体解剖
A typical long bone consists of an outer layer of compact bone, an inner spongy (cancellous) bone, and a central medullary cavity filled with bone marrow. The epiphyses at the ends are covered with articular cartilage to reduce friction in joints. The periosteum is a tough fibrous sheath that covers the bone surface and serves as an attachment point for tendons and ligaments.
典型的长骨由外层的密质骨、内部的松质骨以及充满骨髓的中央髓腔构成。骨端的骨骺表面覆盖有关节软骨以减少关节摩擦。骨膜是覆盖骨表面的坚韧纤维鞘，为肌腱和韧带提供附着点。
| Component | Structural description | Main function |
|---|---|---|
| Compact bone | Dense, made of osteons | Strength, protection |
| Spongy bone | Mesh of trabeculae | Shock absorption, houses marrow |
| Articular cartilage | Hyaline cartilage, smooth | Reduces friction, absorbs shock |
Table: Structures of a long bone. | 表：长骨的结构。
7. Joints and Their Classification | 关节及其分类
Joints are classified structurally as fibrous (immovable), cartilaginous (slightly movable), and synovial (freely movable). Synovial joints are the most common in the limbs; they contain a fluid‑filled cavity, a joint capsule, and reinforcing ligaments. Examples include hinge joints (elbow, knee) and ball‑and‑socket joints (shoulder, hip).
根据结构，关节分为纤维关节（不动）、软骨关节（微动）和滑膜关节（自由活动）。滑膜关节在四肢中最常见，内含充满滑液的关节腔、关节囊和加强韧带。例如铰链关节（肘、膝）和球窝关节（肩、髋）。
A typical exam question may show a diagram of the elbow joint and ask you to label the humerus, radius, ulna, articular cartilage, synovial membrane, and the biceps/triceps tendons.
典型的考题可能给出肘关节示意图，要求标明肱骨、桡骨、尺骨、关节软骨、滑膜以及肱二头肌/肱三头肌肌腱。
8. Tendons and Ligaments: Tough Connective Tissues | 肌腱与韧带：坚韧的结缔组织
Tendons attach skeletal muscle to bone, transmitting the force generated by muscle contraction to produce movement. They are composed mainly of parallel bundles of collagen fibres, giving them enormous tensile strength but little elasticity. Ligaments connect bone to bone, stabilising joints. They contain more elastin fibres, allowing a slight degree of stretch and recoil.
肌腱将骨骼肌附着于骨，传递肌肉收缩产生的力量以产生运动。其主要由平行排列的胶原纤维束构成，赋予肌腱巨大的抗拉强度，但弹性极小。韧带连接骨与骨，稳定关节。韧带含有较多的弹性蛋白纤维，允许一定程度的拉长与回缩。
- Tendons are white and inelastic; ligaments are yellowish and slightly elastic. | 肌腱呈白色，缺乏弹性；韧带呈淡黄色，略有弹性。
- Overstretching a tendon can cause a strain; overstretching a ligament can cause a sprain. | 肌腱过度拉伸会导致劳损；韧带过度拉伸会导致扭伤。
9. Antagonistic Muscle Pairs and Movement Analysis | 拮抗肌群与动作分析
Movement at a joint is produced by the coordinated action of antagonistic muscle pairs. The agonist (prime mover) contracts to produce a specific movement, while the antagonist relaxes and lengthens passively. For example, during elbow flexion, the biceps brachii is the agonist and the triceps brachii is the antagonist. During extension, their roles are reversed.
关节的运动由拮抗肌群的协调作用产生。主动肌（原动肌）收缩产生特定动作，同时拮抗肌松弛并被被动拉长。例如，肘关节屈曲时，肱二头肌是主动肌，肱三头肌是拮抗肌；而在伸肘动作中，角色互换。
Examiners value precise language: say “the biceps contracts and the triceps relaxes” rather than “they work opposite”. A‑level answers should also mention the role of the fulcrum (joint) and the effort‑load relationship in levers.
评分者看重术语的准确使用：应说”肱二头肌收缩、肱三头肌舒张”，而不是”它们作用相反”。A‑level 的答案还应提及支点（关节）的作用以及杠杆系统中力与负荷的关系。
10. Exam Practice: Muscle Ultrastructure and ATP Roles | 真题精练：肌肉超微结构与ATP的作用
Question: Describe the role of ATP in the sliding filament mechanism of muscle contraction and explain why ATP depletion leads to rigor mortis.
问题：描述ATP在肌肉收缩的肌丝滑动机制中的作用，并解释ATP缺乏为何导致尸僵。
Model Answer (English): ATP binds to the myosin head, causing it to detach from actin after the power stroke. ATP is then hydrolysed to ADP and inorganic phosphate, which re‑energises the myosin head into its cocked position. Without ATP, the cross‑bridges cannot be released; myosin heads remain firmly attached to actin, so muscles stay contracted and stiff – this is rigor mortis.
参考答案（中文）：ATP与肌球蛋白头部结合，使其在动力冲程后从肌动蛋白上解离。随后ATP水解为ADP和无机磷酸，重新为肌球蛋白头部供能，使其恢复翘起状态。若无ATP，横桥无法释放，肌球蛋白头部持续牢固结合在肌动蛋白上，肌肉保持收缩和僵硬状态——此即尸僵。
Additional marking points: Mention the role of ATP in pumping Ca²⁺ back into the sarcoplasmic reticulum, because if Ca²⁺ remains in the sarcoplasm, tropomyosin will be kept away from the binding sites and contraction cannot be switched off.
额外得分点：提及ATP在将Ca²⁺泵回肌浆网中的作用，因为若Ca²⁺留在肌浆中，原肌球蛋白将持续离开结合位点，收缩无法停止。
11. Exam Practice: Injury and Tissue Repair | 真题精练：损伤与组织修复
Question: Compare the healing processes of a tendon injury and a bone fracture, highlighting the cellular events involved.
问题：比较肌腱损伤与骨折的愈合过程，突出所涉及的细胞事件。
Model Answer (English): In tendon repair, fibroblasts migrate to the site and synthesise new collagen fibres, but because tendons are poorly vascularised, healing is slow. In bone healing, a haematoma forms first, then a soft callus of fibrocartilage bridges the fracture; this is later replaced by a hard callus of spongy bone through the activity of osteoblasts. Bone is highly vascularised, so healing is faster and more complete.
参考答案（中文）：肌腱修复时，成纤维细胞迁移至损伤处合成新的胶原纤维，但因肌腱血管贫乏，愈合缓慢。骨折愈合则先形成血肿，随后由纤维软骨构成的软骨痂桥接断端；之后通过成骨细胞的活动被松质骨构成的硬骨痂替代。骨的血供丰富，因此愈合更快且更完全。
Explanation of key cells: Osteoblasts deposit new bone matrix; osteoclasts resorb excess callus during remodelling; chondroblasts produce cartilage in the soft callus. In tendons, tenocytes maintain the collagenous matrix but proliferate slowly.
关键细胞解释：成骨细胞沉积新骨质；破骨细胞在骨改建中吸收多余骨痂；成软骨细胞在软骨痂中生成软骨。在肌腱中，腱细胞维持胶原基质，但增殖缓慢。
12. Common Misconceptions and Exam Tips | 常见误区与应试技巧
One frequent error is confusing tendons with ligaments. A high‑mark answer must clearly state their different attachment points: muscle‑to‑bone vs. bone‑to‑bone. Another misconception is thinking that muscle contraction results from filaments themselves shortening; instead the sarcomere shortens because filaments slide past each other. Always link structure to function – for instance, why the sarcoplasmic reticulum has an extensive network (to rapidly release and re‑uptake Ca²⁺).
常见误区包括混淆肌腱与韧带。高得分答案必须明确指出其附着点的区别：肌肉‑骨 vs. 骨‑骨。另一个误区是认为肌肉收缩是肌丝自身缩短；事实上，肌节缩短是由于肌丝相互滑动。始终将结构与功能联系起来——例如，肌浆网为何形成广泛的网络（为了快速释放和回收Ca²⁺）。
- Use terms precisely: “troponin” not “tropomyosin” for Ca²⁺ binding. | 精确使用术语：结合Ca²⁺的是“肌钙蛋白”而非“原肌球蛋白”。
- Specify the type of muscle: skeletal (voluntary, striated), cardiac (involuntary, striated), smooth (involuntary, non‑striated). | 明确肌肉类型：骨骼肌（随意、横纹）、心肌（不随意、横纹）、平滑肌（不随意、无横纹）。
- Draw and label diagrams when practising: sarcomere banding (I‑band, A‑band, H‑zone, Z‑line). | 练习时绘图并标注：肌节明暗带（I带、A带、H区、Z线）。
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