The Muscular System: How Muscles Move the Body – KS3 CIE 生物：肌肉系统完全指南

一、人体肌肉的三大类型：骨骼肌、平滑肌与心肌 | The Three Muscle Types: Skeletal, Smooth and Cardiac

人体内有超过 600 块肌肉，但它们并不都是一样的。根据结构和功能，肌肉可以分为三大类型：骨骼肌、平滑肌和心肌。每一种肌肉在身体里扮演不同的角色，了解它们的区别是 KS3 生物学的第一个关键考点。

The human body contains more than 600 muscles, but they are not all the same. Based on structure and function, muscles can be divided into three main types: skeletal muscle, smooth muscle and cardiac muscle. Each type plays a different role in the body, and knowing the differences between them is the first key point in KS3 Biology.

骨骼肌附着在骨骼上，负责我们主动控制的动作，比如走路、跑步和举东西。在显微镜下，骨骼肌细胞呈长条状，表面有明显的横纹，因此又叫横纹肌。骨骼肌受意识控制，属于随意肌，运动时容易疲劳。

Skeletal muscle attaches to bones and produces the movements we control consciously, such as walking, running and lifting. Under a microscope, skeletal muscle cells are long and cylindrical with visible stripes, so it is also called striated muscle. Skeletal muscle is under conscious control, making it voluntary muscle, and it tires easily during exercise.

平滑肌分布在血管壁、消化道和膀胱等内脏器官中。它没有横纹，收缩缓慢而持久，不受意识控制，属于不随意肌。例如食物在肠道中的蠕动，就是平滑肌收缩推动的。心肌只存在于心脏的壁中，同样有横纹，但不受意识控制，它能够自动而有节律地收缩，终生不停。

Smooth muscle is found in the walls of blood vessels, the digestive tract and the bladder. It has no stripes, contracts slowly and steadily, and is not under conscious control, so it is involuntary muscle. For example, peristalsis, the wave of contraction that pushes food along the intestine, is powered by smooth muscle. Cardiac muscle is found only in the walls of the heart. It is striated like skeletal muscle but is involuntary: it contracts automatically and rhythmically, without stopping, for our whole life.

特征	骨骼肌	平滑肌	心肌
位置	附着在骨骼上	内脏器官壁	心脏壁
横纹	有	无	有
是否受意识控制	是（随意肌）	否（不随意肌）	否（不随意肌）
疲劳速度	快	慢	永不停止

考试中常见的问法是给出三种肌肉的特征描述，要求你判断是哪一种肌肉。记住一个口诀：有横纹、能主动控制的是骨骼肌；无横纹、不随意的是平滑肌；有横纹、自动跳的是心肌。

A common exam question gives descriptions of the three muscle types and asks you to identify which is which. Remember this trick: striated and under voluntary control means skeletal muscle; non-striated and involuntary means smooth muscle; striated and beating automatically means cardiac muscle.

二、骨骼肌的结构：肌纤维、肌原纤维与肌节 | The Structure of Skeletal Muscle: Fibres, Myofibrils and Sarcomeres

如果你把一块骨骼肌一层层剥开，会看到它像一捆电线。最外面是肌肉膜，里面包裹着许多肌束，每个肌束又由许多长长的肌纤维组成。每一根肌纤维其实就是一个特殊的细胞，长度可达数厘米，内含许多细胞核。

If you peel a skeletal muscle apart layer by layer, you will find it looks like a bundle of cables. The outside is a membrane, inside which are many muscle bundles (fascicles), and each bundle is made of many long muscle fibres. Each muscle fibre is actually one special cell: it can be several centimetres long and contains many nuclei.

在肌纤维内部，密密麻麻地排列着更细的丝状结构，叫做肌原纤维。肌原纤维上重复排列着一个个功能单位，称为肌节。肌节是肌肉收缩的基本单位，它由两种更细的蛋白质丝组成：粗丝（肌球蛋白）和细丝（肌动蛋白）。

Inside each muscle fibre are densely packed thinner thread-like structures called myofibrils. Along a myofibril, functional units repeat in sequence; each unit is called a sarcomere. The sarcomere is the basic unit of muscle contraction, and it is built from two kinds of even thinner protein filaments: thick filaments (myosin) and thin filaments (actin).

KS3 阶段你不需要记住所有细小的名字，但需要理解：肌肉不是一整块同时缩短，而是每一根肌纤维里的肌节同时缩短，无数个肌节一起缩短，整块肌肉才明显变短变粗。这也是为什么肌肉收缩后摸起来更硬。

At KS3 level you do not need to memorise every tiny name, but you do need to understand this: a muscle does not shorten as one solid block. Instead, the sarcomeres inside every fibre shorten at the same time, and when countless sarcomeres shorten together, the whole muscle visibly becomes shorter and thicker. This is also why a contracted muscle feels harder to touch.

三、肌肉如何收缩：KS3 版滑动丝模型 | How Muscles Contract: The Sliding Filament Model at KS3 Level

肌肉收缩的机制在 GCSE 和 A-Level 会详细学习，但 KS3 的题目已经开始考察它的核心思想：滑动丝模型。这个模型把肌节的缩短解释为粗丝和细丝互相滑过，而不是丝本身变短。

The mechanism of muscle contraction is studied in detail at GCSE and A-Level, but KS3 questions already test its core idea: the sliding filament model. This model explains sarcomere shortening as the thick and thin filaments sliding past each other, rather than the filaments themselves getting shorter.

当神经信号到达肌肉时，肌纤维内部会释放钙离子，钙离子让细丝上的结合位点暴露出来，粗丝上的横桥便抓住细丝，像划船一样把细丝向肌节中央拉动。所有横桥一起发力，肌节就变短了，整块肌肉随之收缩。

When a nerve signal reaches the muscle, calcium ions are released inside the fibre. The calcium exposes binding sites on the thin filaments, so the cross-bridges on the thick filaments can grab the thin filaments and pull them towards the centre of the sarcomere, like rowing a boat. When all the cross-bridges pull together, the sarcomere shortens and the whole muscle contracts.

在 KS3 试卷上，滑动丝模型最常见的考法有三类：一是解释为什么肌肉收缩需要能量；二是解释肌节收缩时粗丝与细丝长度不变；三是比较收缩和舒张时肌节的长度变化。答题时记住关键词：钙离子、横桥、滑过、变短。

In KS3 papers, the sliding filament model is usually tested in three ways: explaining why contraction needs energy; explaining that thick and thin filaments do not change length during shortening; and comparing sarcomere length between contraction and relaxation. When answering, use the key words: calcium ions, cross-bridges, slide past, shorten.

四、拮抗肌对：肱二头肌与肱三头肌的协同工作 | Antagonistic Pairs: How Biceps and Triceps Work Together

肌肉只能主动收缩，不能主动伸长。也就是说，一块肌肉只能把骨骼向一个方向拉。那么，手臂怎么才能又弯又伸呢？答案是一对方向相反的肌肉互相配合，这种组合叫做拮抗肌对。

Muscles can only actively contract; they cannot actively lengthen themselves. In other words, one muscle can only pull a bone in one direction. So how can the arm both bend and straighten? The answer is a pair of muscles working in opposite directions, a combination called an antagonistic pair.

上臂最典型的拮抗肌对是肱二头肌和肱三头肌。当你弯曲肘部（屈肘）时，肱二头肌收缩变短，肱三头肌舒张变长。当你伸直手臂（伸肘）时，情况正好相反：肱三头肌收缩，肱二头肌舒张。骨骼本身不会动，是肌肉的拉动让它绕关节转动。

The most typical antagonistic pair in the upper arm is the biceps and the triceps. When you bend your elbow (flexion), the biceps contracts and shortens while the triceps relaxes and lengthens. When you straighten your arm (extension), the opposite happens: the triceps contracts and the biceps relaxes. Bone does not move by itself; it rotates around a joint because muscles pull on it.

类似的拮抗肌对还有很多，比如小腿的胫骨前肌和腓肠肌控制足踝的屈伸。KS3 题目常常给出手臂姿势图，让你标注哪块肌肉收缩、哪块舒张。判断方法是看关节向哪个方向弯曲，弯曲一侧的肌肉就是收缩的那块。

There are many other antagonistic pairs, such as the tibialis anterior and gastrocnemius in the lower leg controlling ankle movement. KS3 questions often show a diagram of an arm position and ask you to label which muscle contracts and which relaxes. The trick is to look at which way the joint bends: the muscle on the bending side is the one contracting.

五、肌腱与韧带：肌肉如何连接骨骼 | Tendons and Ligaments: How Muscles Attach to Bone

肌肉不会直接长在骨头上。肌肉的两端通过一种坚韧的结缔组织与骨骼相连，这种组织叫做肌腱。肌腱非常结实但几乎没有弹性，它把肌肉收缩产生的拉力传递给骨骼，从而带动关节运动。

Muscles do not attach directly to bone. Each end of a muscle is connected to bone by a tough connective tissue called a tendon. Tendons are very strong but have almost no elasticity: they transmit the pull produced by muscle contraction to the bone, so that the joint moves.

很多人会把肌腱和韧带混淆，这是 KS3 考试的高频失分点。肌腱连接肌肉和骨骼，而韧带连接骨骼和骨骼。韧带位于关节周围，把两块骨固定在关节的正确位置上，防止关节脱臼。以膝盖为例：连接大腿肌与小腿骨的髌腱是肌腱，而膝关节两侧稳定关节的是韧带。

Many students confuse tendons with ligaments, and this is a frequent mark-losing point in KS3 exams. Tendons connect muscle to bone, while ligaments connect bone to bone. Ligaments surround joints and hold the two bones in the correct position, preventing dislocation. Take the knee as an example: the patellar tendon connects thigh muscle to shin bone, while the ligaments on either side of the knee joint stabilise it.

记住一句话就能得分：肌肉拉肌腱，肌腱拉骨头，韧带管关节。在填写概念图或表格的题目中，只要把”肌肉-肌腱-骨骼”和”骨骼-韧带-骨骼”这两条链写对，基本就能拿满分。

One sentence is enough to score marks: muscles pull tendons, tendons pull bones, and ligaments hold joints together. In concept-map or table questions, if you write the two chains correctly, “muscle-tendon-bone” and “bone-ligament-bone”, you will almost certainly get full marks.

六、肌肉的能量来源：细胞呼吸与 ATP | The Energy Source of Muscles: Cellular Respiration and ATP

肌肉收缩需要能量，这些能量来自细胞呼吸。细胞呼吸是葡萄糖在细胞内与氧气反应、释放能量的过程，它发生在每个细胞的线粒体中。肌肉细胞里有特别多的线粒体，因为运动时它们需要大量能量。

Muscle contraction needs energy, and this energy comes from cellular respiration. Cellular respiration is the process in which glucose reacts with oxygen inside cells to release energy; it happens in the mitochondria of every cell. Muscle cells contain a particularly large number of mitochondria because they need huge amounts of energy during exercise.

细胞呼吸释放的能量被储存在一种叫做 ATP 的分子中。可以把 ATP 想象成细胞的”能量零钱”：它随时可以拆开，把能量直接交给需要的地方，比如正在收缩的肌纤维。肌肉细胞储存的 ATP 很少，只能维持几秒钟的剧烈运动，所以必须持续通过呼吸作用补充。

The energy released by respiration is stored in a molecule called ATP. Think of ATP as the cell’s “pocket change”: it can be split open at any moment to hand energy directly to wherever it is needed, such as a contracting muscle fibre. Muscle cells store very little ATP, only enough for a few seconds of intense activity, so it must be continuously topped up by respiration.

KS3 常考的知识点是呼吸作用的文字方程式：葡萄糖 + 氧气 → 二氧化碳 + 水 + 能量。运动越剧烈，肌肉需要的能量越多，呼吸作用就越快，身体就需要更快地吸入氧气、排出二氧化碳，这就是为什么运动会让你气喘吁吁。

The knowledge point frequently tested at KS3 is the word equation for respiration: glucose + oxygen → carbon dioxide + water + energy. The more intense the exercise, the more energy the muscles need, the faster respiration runs, and the faster the body must take in oxygen and remove carbon dioxide. That is why exercise makes you breathe heavily.

七、运动中的变化：心率、呼吸频率与肌肉疲劳 | Changes During Exercise: Heart Rate, Breathing Rate and Muscle Fatigue

当你开始运动时，身体会发生一系列可观察的变化：心跳加快、呼吸变快变深、出汗增加、肌肉温度升高。这些变化的目的只有一个：给肌肉输送更多氧气和葡萄糖，同时更快地运走二氧化碳和多余的热量。

When you start exercising, a series of observable changes occur: the heart beats faster, breathing becomes faster and deeper, sweating increases, and muscle temperature rises. All these changes have one purpose: to deliver more oxygen and glucose to the muscles and to remove carbon dioxide and excess heat more quickly.

心率加快意味着心脏每搏输出的血液更多，血液把肺里的氧气和肠道吸收的葡萄糖运到肌肉，再把肌肉产生的二氧化碳运回肺排出。剧烈运动时肌肉需要的氧气可能超过供应，这时肌肉会进行无氧呼吸，产生乳酸。

A faster heart rate means more blood pumped per minute; the blood carries oxygen from the lungs and glucose absorbed from the gut to the muscles, and carries carbon dioxide produced by the muscles back to the lungs for removal. During intense exercise the muscles may need more oxygen than the supply can provide; in that case they switch to anaerobic respiration, which produces lactic acid.

乳酸积累是肌肉疲劳和酸痛的重要原因。无氧呼吸释放的能量比有氧呼吸少得多，所以剧烈运动只能维持很短时间。运动停止后，身体还会继续加快呼吸一段时间，目的是把积累的乳酸彻底分解，偿还”氧债”。这也是为什么冲刺之后你会大口喘气。

The build-up of lactic acid is a major cause of muscle fatigue and soreness. Anaerobic respiration releases far less energy than aerobic respiration, which is why intense exercise can only be sustained for a short time. After exercise stops, the body keeps breathing faster for a while in order to break down the accumulated lactic acid completely and repay the “oxygen debt”. This is why you gasp for air after a sprint.

八、KS3 肌肉工作表常见题型与答题模板 | Common KS3 Muscles Worksheet Questions and Answer Templates

以 “KS3 CIE Muscles worksheet” 这类工作表为例，题目通常围绕五类问题展开。掌握每类题型的答题模板，比刷十张试卷更有效。下面逐一拆解。

Worksheets like “KS3 CIE Muscles” usually revolve around five question types. Mastering an answer template for each type is more effective than doing ten papers. Let us break them down one by one.

第一类是标注题：给出手臂或腿部示意图，要求标出肱二头肌、肱三头肌、肌腱、韧带的位置。答题要点是位置准确，肌腱画在肌肉两端与骨骼的连接处，韧带画在关节周围。第二类是判断题：给出”肌腱连接两块骨骼”这类陈述，要求判断对错并解释。这类题的关键是严格区分肌腱与韧带。

The first type is labelling: a diagram of the arm or leg is given and you must label the biceps, triceps, tendon and ligament. The key is accuracy: tendons at the muscle-bone connections at both ends, ligaments around the joint. The second type is true-or-false: statements like “tendons connect two bones” must be judged and explained. The key here is strictly distinguishing tendons from ligaments.

第三类是解释题：解释为什么手臂弯曲时肱二头肌收缩而肱三头肌舒张。答题要写清拮抗肌对的概念，并指出肌肉只能收缩拉动而不能主动伸长。第四类是实验题：比较不同强度运动前后的心率变化，常要求设计对照实验并解释变量控制。第五类是应用题：解释运动员运动后肌肉酸痛的原因，答案要落到乳酸积累和无氧呼吸上。

The third type is explanation: explain why the biceps contracts while the triceps relaxes when the arm bends. Your answer must mention the antagonistic pair concept and point out that muscles can only pull, not actively push or lengthen. The fourth type is practical: comparing heart rate before and after exercise of different intensities, often requiring a controlled experiment design with explained variables. The fifth type is application: explain why an athlete’s muscles ache after exercise; the answer must land on lactic acid build-up and anaerobic respiration.

答题模板可以概括为四步：第一步圈出题目关键词（收缩、舒张、能量、疲劳）；第二步写出对应的核心概念名称；第三步用一句完整的因果链把概念连起来；第四步检查是否用了题目给出的信息。按这个顺序答题，得分率会明显提高。

The answer template can be summarised in four steps: first, circle the key words in the question (contract, relax, energy, fatigue); second, name the core concept; third, connect the concepts with one complete cause-and-effect sentence; fourth, check that you have used the information given in the question. Following this order noticeably improves your marks.

九、易错点辨析与记忆技巧 | Common Mistakes and Memory Tricks

在肌肉这一章，KS3 学生最常犯的错误有四个。第一个是把肌腱和韧带弄反：记住”肌腱连肌骨、韧带连骨骨”。第二个是认为肌肉可以主动伸长：实际上肌肉只能主动收缩，伸长靠的是拮抗肌的拉动或重力。

In the muscles chapter, KS3 students make four very common mistakes. The first is swapping tendons and ligaments: remember “tendons join muscle to bone, ligaments join bone to bone”. The second is thinking muscles can actively lengthen: in fact muscles can only actively contract; lengthening happens because the antagonistic muscle pulls, or because of gravity.

第三个错误是混淆有氧呼吸与无氧呼吸的产物：有氧呼吸产生二氧化碳和水，无氧呼吸产生乳酸（在人体肌肉中）。第四个错误是忘记能量来自细胞呼吸而非肌肉本身：肌肉只是把化学能转化为动能，能量源头是葡萄糖。

The third mistake is confusing the products of aerobic and anaerobic respiration: aerobic respiration produces carbon dioxide and water, while anaerobic respiration in human muscle produces lactic acid. The fourth mistake is forgetting that the energy comes from respiration, not from the muscle itself: the muscle only converts chemical energy into kinetic energy, and the original energy source is glucose.

记忆技巧方面，可以把三大肌肉类型编成一句话：”骨骼有纹随意动，内脏平滑自动蠕，心脏心肌终身跳。” 拮抗肌对可以联想跷跷板：一边下去，另一边就上来，永远不会两边同时收缩。心脏永不疲劳则是因为心肌细胞之间有特殊的连接结构，让电信号快速传遍整个心脏，保证同步收缩。

For memory, compress the three muscle types into one sentence: “Skeletal is striated and voluntary, smooth lines the organs and moves on its own, cardiac beats in the heart for life.” For antagonistic pairs, picture a seesaw: when one side goes down, the other comes up; the two never contract at the same time. The heart never tires because cardiac muscle cells are joined by special structures that let electrical signals spread across the whole heart quickly, keeping the contraction synchronised.

十、骨骼与关节：肌肉运动的搭档 | Bones and Joints: The Partners of Muscle Movement

肌肉拉动骨骼，骨骼绕关节转动，身体才能运动。所以讲肌肉就不能不讲骨骼和关节。人体有 206 块骨骼，它们构成骨架，支撑身体、保护内脏，并且作为肌肉的杠杆。关节则是两块骨骼相接的地方，让骨骼可以灵活转动。

Muscles pull bones, bones rotate around joints, and only then can the body move. So muscles cannot be studied without bones and joints. The human body has 206 bones; they form the skeleton, supporting the body, protecting internal organs, and acting as levers for the muscles. A joint is where two bones meet, allowing the bones to move flexibly.

KS3 阶段重点掌握两类关节。第一类是铰链关节，只允许前后一个方向的活动，像门的铰链一样，肘关节和膝关节就是典型例子。第二类是球窝关节，允许向各个方向活动，活动范围最大，肩关节和髋关节属于这一类。记法：铰链像门轴只能开合，球窝像万向节四面八方都能转。

At KS3 level you need to master two types of joints. The first is the hinge joint, which only allows movement in one direction, like a door hinge; the elbow and knee are typical examples. The second is the ball-and-socket joint, which allows movement in all directions and has the largest range of motion; the shoulder and hip belong to this type. Memory aid: a hinge joint opens and closes like a door, while a ball-and-socket joint rotates like a universal joint in every direction.

在关节内部，骨骼的末端覆盖着一层光滑的软骨，可以减少摩擦；关节腔里的滑液进一步起到润滑作用，就像给机器加油一样。如果软骨磨损或滑液不足，关节活动就会疼痛，这就是关节炎的一种常见成因。这些细节常出现在”解释关节为什么能顺畅活动”的题目里，答案要提到软骨和滑液两个关键词。

Inside a joint, the ends of the bones are covered by a layer of smooth cartilage that reduces friction, and the synovial fluid in the joint cavity lubricates the joint further, like oiling a machine. If the cartilage wears away or the fluid is insufficient, joint movement becomes painful; this is one common cause of arthritis. These details often appear in questions asking “explain why joints can move smoothly”, and the answer must mention the two key words: cartilage and synovial fluid.

十一、坚持运动：肌肉如何变强，身体如何受益 | Regular Exercise: How Muscles Get Stronger and the Body Benefits

经常锻炼的人肌肉更发达、更有力量，这是为什么？原因是肌肉遵循”用进废退”的原则：经常使用的肌肉，其肌纤维会变粗，肌纤维内的线粒体数量会增加，毛细血管也会增多，供氧和供能效率随之提高。这就是所谓的力量训练带来的肌肉肥大。

Why are people who exercise regularly stronger and more muscular? Because muscles follow the principle of “use it or lose it”: in regularly used muscles, the fibres become thicker, the number of mitochondria inside the fibres increases, and capillaries become more numerous, so oxygen supply and energy production become more efficient. This is the muscle hypertrophy produced by strength training.

除了让肌肉变强，规律运动还会带来一系列全身性的好处：心脏更强壮，每次搏动泵出的血量更多，静息心率下降；肺活量增大，呼吸效率提高；骨骼更致密，不易骨折；同时运动还能帮助控制体重、缓解压力、改善睡眠。KS3 课程要求学生能解释运动对心脏和肺的这些影响。

Besides strengthening muscles, regular exercise brings a whole range of whole-body benefits: the heart becomes stronger and pumps more blood per beat, so the resting heart rate falls; lung capacity increases and breathing becomes more efficient; bones become denser and less likely to break; and exercise also helps control weight, relieve stress and improve sleep. The KS3 curriculum requires students to be able to explain these effects of exercise on the heart and lungs.

另一方面，久坐不动会让肌肉萎缩、力量下降，心肺功能变差。医学指南建议青少年每天至少进行 60 分钟中等强度以上的运动。理解”训练-适应”的关系，不仅能在考试中答好”解释运动好处”的开放题，也是养成健康生活习惯的生物学依据。

On the other hand, a sedentary lifestyle makes muscles shrink, strength decline and heart-lung fitness worsen. Medical guidelines recommend that teenagers do at least 60 minutes of moderate-to-vigorous exercise every day. Understanding the “training-adaptation” relationship not only helps you answer open questions about the benefits of exercise in exams, but also gives you the biological basis for building healthy habits.

Summary | 总结

肌肉系统是 KS3 生物学的核心章节，也是后续 GCSE 与 A-Level 运动生理学的基础。三大肌肉类型（骨骼肌、平滑肌、心肌）的区别、拮抗肌对的配合方式、肌腱与韧带的分工、呼吸作用为收缩供能，以及乳酸与肌肉疲劳的关系，构成了这一章的全部考点框架。

The muscular system is a core chapter of KS3 Biology and the foundation for exercise physiology at GCSE and A-Level. The differences between the three muscle types (skeletal, smooth and cardiac), the coordination of antagonistic pairs, the division of labour between tendons and ligaments, respiration powering contraction, and the link between lactic acid and muscle fatigue together form the complete framework of this chapter.

复习时建议先画出”肌肉-肌腱-骨骼-关节”的关系图，再默写三大肌肉类型对比表，最后用真题训练五类题型的答题模板。只要把这四步做完，任何肌肉主题的工作表都不会再难倒你。

When revising, first draw a relationship diagram of “muscle-tendon-bone-joint”, then write out the three-muscle-type comparison table from memory, and finally practise the five answer templates with past questions. Finish these four steps and no muscles worksheet will defeat you again.

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