Antagonistic Muscles | 拮抗肌真题精练

📚 Antagonistic Muscles | 拮抗肌真题精练

Antagonistic muscles are pairs of muscles that work in opposition to produce movement at a joint. Understanding how they coordinate contraction and relaxation is a key topic in Organisms 1.1.3. This revision guide provides clear explanations and exam-style questions with detailed answers to help you master the concept and excel in your assessments.

拮抗肌是以相互对抗的方式工作、从而在关节处产生运动的一对肌肉。理解它们如何协调收缩与放松是生物体 1.1.3 节的核心内容。本复习指南提供清晰的解释及考试风格的题目，并附详细解析，助你掌握该概念并在考试中脱颖而出。

1. What Are Antagonistic Muscles? | 什么是拮抗肌？

Antagonistic muscles are pairs of muscles that act on a joint to produce opposing movements. When one muscle contracts (shortens), the other muscle in the pair relaxes (lengthens). This arrangement allows controlled, smooth motion and prevents damage caused by overextension.

拮抗肌是作用于同一关节、产生相反运动的一对肌肉。当其中一块肌肉收缩（变短）时，配对中的另一块肌肉舒张（变长）。这种安排能够实现受控、平滑的运动，并防止因过度拉伸而造成的损伤。

The muscle that contracts and causes the desired movement is called the agonist (or prime mover). The muscle that relaxes to allow the movement is the antagonist. For example, during elbow flexion, the biceps brachii is the agonist and the triceps brachii is the antagonist.

收缩并引起所需运动的肌肉称为主动肌（或原动肌）。放松以允许运动的肌肉是对抗肌。例如，在肘关节屈曲时，肱二头肌是主动肌，肱三头肌是对抗肌。

2. How Antagonistic Pairs Work | 拮抗肌对的工作原理

Muscles can only pull; they cannot push. Therefore, to move a bone back to its original position, a second muscle must pull in the opposite direction. This is why muscles are arranged in antagonistic pairs across joints.

肌肉只能产生拉力，不能产生推力。因此，要牵引骨骼回到原位，必须有另一块肌肉朝相反方向拉动。这就是肌肉以拮抗对的形式跨关节排列的原因。

When the agonist contracts, it pulls on a bone via a tendon, moving the bone at the joint. Simultaneously, the antagonist relaxes, allowing the agonist’s action without resistance. The roles reverse when the opposite movement is required.

当主动肌收缩时，它通过肌腱牵拉骨骼，使骨骼在关节处运动。同时，对抗肌放松，使主动肌的动作不受阻碍。当需要相反方向运动时，两者的角色互换。

3. Classic Example: Biceps and Triceps | 经典示例：肱二头肌与肱三头肌

In the upper arm, the biceps brachii and triceps brachii form an antagonistic pair at the elbow joint. The biceps is located on the front of the humerus, and the triceps is at the back. Both attach to the shoulder blade and to bones of the forearm via tendons.

在上臂，肱二头肌和肱三头肌在肘关节处构成一对拮抗肌。肱二头肌位于肱骨前方，肱三头肌位于后方。两者均通过肌腱附着于肩胛骨和前臂骨。

During flexion (bending the arm): Biceps contracts and pulls on the radius, lifting the forearm. Triceps relaxes and extends to allow smooth bending. The opposite occurs during extension (straightening the arm): Triceps contracts and pulls on the ulna; biceps relaxes.

屈曲（弯曲手臂）时：肱二头肌收缩，牵拉桡骨，抬起前臂。肱三头肌放松并伸长，以允许平滑弯曲。伸展（伸直手臂）时则相反：肱三头肌收缩，牵拉尺骨；肱二头肌放松。

4. Flexion and Extension – Joint Angles | 屈曲与伸展 – 关节角度

Flexion decreases the angle between two bones, typically by contracting a flexor muscle. Extension increases the angle, usually via an extensor muscle. In the elbow, the biceps is a flexor; the triceps is an extensor.

屈曲减小两骨之间的角度，通常由屈肌收缩实现。伸展增大角度，通常通过伸肌收缩。在肘关节，肱二头肌是屈肌，肱三头肌是伸肌。

These terms are frequently tested. A helpful rule: the muscle that crosses the front of a joint generally flexes it, while the muscle at the back extends it. This applies to knee, elbow, and ankle.

这些术语经常出现在考题中。一条有用的规律：跨越关节前方的肌肉通常使其屈曲，而后方的肌肉使其伸展。这适用于膝、肘和踝关节。

5. Other Important Antagonistic Pairs | 其他重要的拮抗肌对

Besides the biceps and triceps, you must know at least three other pairs for exams. At the knee joint, the quadriceps (front thigh) extend the leg while the hamstrings (back thigh) flex it. They work antagonistically during walking, running, and kicking.

除肱二头肌与肱三头肌外，考试中至少还需掌握另外三对。在膝关节，股四头肌（大腿前侧）使腿伸展，而腘绳肌（大腿后侧）使腿屈曲。它们在行走、跑步和踢球时拮抗工作。

At the ankle, the tibialis anterior lifts the foot (dorsiflexion), and the gastrocnemius points the foot down (plantarflexion). In the trunk, the rectus abdominis (abs) and erector spinae form an antagonistic pair for bending forward and extending the spine.

在踝关节，胫骨前肌抬脚（背屈），腓肠肌绷直脚尖（跖屈）。在躯干，腹直肌（腹肌）和竖脊肌构成弯曲与挺直脊柱的拮抗对。

6. Exam-Style Question 1: Multiple Choice | 真题示例1：选择题

Question: Which statement correctly describes the actions of muscles when you straighten your arm at the elbow from a bent position?

题目：从弯曲位置伸直手臂时，下列哪一项正确描述了肌肉的动作？

A) Biceps contracts, triceps contracts.
B) Biceps relaxes, triceps relaxes.
C) Biceps contracts, triceps relaxes.
D) Biceps relaxes, triceps contracts.

Answer: D. The triceps is the extensor—it contracts to straighten the arm; the biceps relaxes.

答案：D。肱三头肌是伸肌——它收缩以使手臂伸直；肱二头肌则放松。

Explanation: Always identify the agonist for the given movement. Extension makes the triceps the agonist, so it contracts. Option C would be correct for flexion. Many students lose marks by confusing the roles.

解析：务必先确定给定运动的主动肌。伸展时，肱三头肌是主动肌，因此它收缩。选项C是屈曲时的正确描述。许多学生因混淆角色而失分。

7. Exam-Style Question 2: Labelling and Short Answer | 真题示例2：简答与标注题

Study the diagram of the upper arm muscles. Label A and B, and explain what happens to each muscle when the arm is flexed at the elbow.

观察上臂肌肉示意图。标注A与B，并解释手臂在肘部弯曲时每块肌肉发生什么变化。

(A points to biceps, B to triceps)

(A指向肱二头肌，B指向肱三头肌)

Model answer: A – Biceps brachii, B – Triceps brachii. When the arm bends (flexion), the biceps (A) contracts and shortens, pulling on the radius via its tendon. The triceps (B) relaxes and is stretched, allowing the elbow to flex without opposition.

参考答案：A – 肱二头肌，B – 肱三头肌。当手臂弯曲（屈曲）时，肱二头肌（A）收缩变短，通过肌腱牵拉桡骨。肱三头肌（B）放松并被拉长，允许肘部无阻碍地屈曲。

8. Exam-Style Question 3: Sports Scenario | 真题示例3：运动情景题

Question: A footballer kicks a ball. Describe the roles of the quadriceps and hamstrings during the kicking motion, using the terms agonist and antagonist. Then explain what happens as the player lowers the leg back to the ground.

题目：一名足球运动员踢球。描述踢球过程中股四头肌和腘绳肌的作用，使用主动肌和对抗肌这两个术语。然后解释球员将腿放回地面时的情况。

Answer: When kicking, the leg extends at the knee. The quadriceps contract (agonist) while the hamstrings relax (antagonist). When lowering the leg, the hamstrings contract (now agonist) to flex the knee, and the quadriceps relax (antagonist). This switching of roles is the hallmark of an antagonistic pair.

答案：踢球时，腿在膝关节处伸展。股四头肌收缩（主动肌），而腘绳肌放松（对抗肌）。将腿放回地面时，腘绳肌收缩（此时为主动肌）使膝屈曲，股四头肌放松（对抗肌）。这种角色转换正是拮抗肌对的标志。

9. Exam-Style Question 4: Table Completion | 真题示例4：表格填空

Complete the table to show the agonist and antagonist for each movement. Then answer the follow-up question.

Movement	Agonist	Antagonist
Elbow flexion	Biceps	Triceps
Knee extension	Quadriceps	Hamstrings
Ankle plantarflexion	Gastrocnemius	Tibialis anterior

完成表格，标出每个运动的主动肌和对抗肌。

Follow-up question: Why can the quadriceps not be the agonist for both knee extension and knee flexion?

后续问题：为什么股四头肌不能同时作为伸膝和屈膝的主动肌？

Answer: Because a muscle can only pull in one direction; it cannot push. To flex the knee, a muscle on the opposite side (hamstrings) must contract. The quadriceps would need to lengthen, which is only possible by relaxing while the antagonist contracts.

答案：因为肌肉只能在一个方向上产生拉力，不能推动。要屈膝，必须由对侧的肌肉（腘绳肌）收缩。股四头肌只能通过放松、让对抗肌收缩来伸长。

10. Common Mistakes and How to Avoid Them | 常见错误与避错指南

Mistake 1: Thinking both muscles contract together during movement. In reality, they operate in a reciprocal inhibition: when the agonist contracts, the antagonist relaxes via a spinal reflex.

错误1：误认为运动时两块肌肉一起收缩。实际上，它们以交互抑制的方式运作：当主动肌收缩时，对抗肌通过脊髓反射放松。

Mistake 2: Confusing agonist and antagonist based on muscle size or assumed ‘strength’. The agonist is defined solely by which muscle produces the observed movement.

错误2：根据肌肉大小或主观的“强弱”来混淆主动肌与对抗肌。主动肌仅由产生特定运动的肌肉决定。

Mistake 3: Forgetting to mention tendons or attachment points in explanations. Many mark schemes require ‘via tendons’ for full marks.

错误3：在解释时忘记提及肌腱或附着点。许多评分方案要求写“通过肌腱”才能得满分。

Tip: Always state the movement first (flexion/extension), then identify the agonist and antagonist. Use precise words: ‘contracts’, ‘relaxes’, ‘pulls on [bone name]’.

技巧：先明确运动类型（屈曲/伸展），再指出主动肌和对抗肌。使用精准用词：“收缩”“放松”“牵拉[骨名]”。

11. Key Diagrams for Your Revision Notes | 必记的关键图解

Examiners often expect you to sketch or label a simple antagonistic pair. Practise drawing the elbow joint with the humerus, radius, ulna, biceps and triceps, clearly showing tendons. Add arrows to indicate contraction direction.

考官常要求你画出或标注简单的拮抗肌对。练习绘制肘关节，包含肱骨、桡骨、尺骨、肱二头肌和肱三头肌，清晰标出肌腱，并用箭头指示收缩方向。

For the knee, draw the femur, tibia, quadriceps tendon, patella, and hamstrings. In revision, colour-code the agonist and antagonist for a given movement to reinforce the concept.

对于膝关节，画出股骨、胫骨、股四头肌肌腱、髌骨和腘绳肌。复习时为给定运动中的主动肌和对抗肌着色编码，以强化概念。

12. Summary and Final Tips | 总结与终极备考建议

Antagonistic muscle pairs work across a joint: one muscle contracts as the agonist, the other relaxes as the antagonist. The classic example is biceps and triceps at the elbow, but the principle applies to all synovial joints.

拮抗肌对跨关节工作：一块肌肉作为主动肌收缩，另一块作为对抗肌放松。经典示例是肘部的肱二头肌与肱三头肌，但该原理适用于所有滑膜关节。

Memorise the main pairs: biceps/triceps (elbow), quadriceps/hamstrings (knee), tibialis anterior/gastrocnemius (ankle). In any exam question, first identify the movement, then determine which muscle pulls on which bone. Use accurate biological vocabulary.

记住主要的拮抗对：肱二头肌/肱三头肌（肘），股四头肌/腘绳肌（膝），胫骨前肌/腓肠肌（踝）。在任何考题中，先确定运动，再判断哪块肌肉在牵拉哪块骨。使用准确的生物学术语。

Practise past paper questions and always check the mark scheme. Many errors come from describing both muscles contracting together or mixing up flexor/extensor roles. Good revision will ensure you can apply the concept to unfamiliar joints, such as the shoulder or hip.

练习往年真题，并始终核对评分标准。许多错误源于描述两块肌肉同时收缩，或混淆屈肌/伸肌的角色。扎实的复习能确保你将该概念应用于陌生关节，如肩或髋。

Published by TutorHao | Organisms 1.1.3 Revision Series | aleveler.com

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Antagonistic Muscles | 拮抗肌 真题精练