Question

Give an example to show that skeletal muscles work in antagonistic pairs. Explain. (page 255)

Short answer

The biceps and triceps muscles in the arm are an example of skeletal muscles working in antagonistic pairs. During arm flexion, the biceps contract and the triceps relax, pulling the forearm up and bringing the hand closer to the shoulder. Conversely, during arm extension, the triceps contract and the biceps relax, moving the forearm away from the shoulder. The roles of these muscles reverse depending on the movement, with one acting as the agonist (prime mover) and the other as the antagonist (opposing muscle). This coordinated function enables smooth and controlled arm movements.

Step-by-step solution

1. Defining Skeletal Muscles and Antagonistic Pairs

Skeletal muscles are muscles that attach to the bones, and they are responsible for moving the body and maintaining posture. Antagonistic pairs are two muscles that work together to create movement by pulling on the bones in opposite directions. One muscle contracts (shortens) while the other relaxes (lengthens), and they switch roles during the movement to coordinate the action.

2. Providing an Example of Antagonistic Pairs

A good example of skeletal muscles working in antagonistic pairs is the action of the biceps and triceps muscles in the arm. The biceps muscle is located on the front of the upper arm, while the triceps muscle is located on the back.

3. The Biceps and Triceps During Arm Flexion and Extension

When you bend your arm at the elbow (flexion), the biceps muscle contracts, and the triceps muscle relaxes. This shortens the biceps muscle and pulls the forearm up, bringing the hand closer to the shoulder. On the other hand, when you straighten your arm (extension), the triceps muscle contracts, and the biceps muscle relaxes, so the forearm moves away from the shoulder.

4. Role Reversal of Biceps and Triceps

The roles of the biceps and triceps muscles reverse depending on the movement. In the flexion movement, the biceps muscle becomes the agonist (prime mover), while the triceps muscle acts as the antagonist (muscle opposing the prime mover). Conversely, during the extension movement, the triceps muscle becomes the agonist, while the biceps muscle acts as the antagonist.

5. Conclusion

This example shows that skeletal muscles, specifically the biceps and triceps muscles in our arms, work in antagonistic pairs to create movement. The coordinated contraction and relaxation of these two muscles allow for smooth and controlled arm movements.

Key concepts

Skeletal Muscles

Skeletal muscles are vital parts of our bodies, responsible for our movement and posture. They are a type of muscle tissue that, as the name suggests, connects to our bones through tendons. They manage both simple and complex movements by pulling on bones.
Skeletal muscles are voluntary muscles, meaning we actively control them using our nervous system. This sets them apart from involuntary muscles, like the heart, which operate without conscious thought. These muscles are incredibly strong and swift in their contractions, making them ideal for precise movements.

They work in groups, coordinating actions to perform everyday tasks. By contracting, they initiate movements, and by relaxing, they return to a resting state, ready for the next action. A feature of skeletal muscles is that they mostly work in pairs to ensure smooth motion.

Biceps and Triceps

Our upper arms contain two key muscles: the biceps and the triceps. These muscles are classic examples of an antagonistic pair. Located on the front of the upper arm, the biceps muscle is prominent and helps lift objects by bending the elbow. On the flip side, the triceps muscle, positioned on the back of the upper arm, aids in straightening the elbow.
The biceps and triceps demonstrate their antagonistic nature during different arm movements. When one muscle contracts, the other must relax to facilitate a particular movement smoothly. This coordination allows for the efficient and balanced function of the arm.

• **Biceps:** Front of the arm, active during lifting and bending the arm.
• **Triceps:** Back of the arm, supports pushing and arm straightening tasks.

Understanding this pair demonstrates how skeletal muscles work together, while performing opposing tasks to control movement.

Muscle Contraction

Muscle contraction is a fundamental aspect of how muscles perform work. It involves the shortening or thickening of muscle fibers to exert force. When a muscle contracts, it pulls on the bone it's connected to, bringing about movement.
In the biceps and triceps, contraction plays a key role. During arm flexion, the biceps contract. This action pulls the forearm towards the shoulder. Meanwhile, the triceps relax to allow this movement.

For arm extension, the roles reverse. The triceps contract, straightening the arm, while the biceps relax. Contraction and relaxation must be perfectly timed for seamless and fluid motion.
Properly timed contractions are essential for controlled and precise movements that we rely on daily. This fascinating orchestration highlights the sophistication of the human motor system.

Arm Movement

Arm movement is a complex process, controlled by the precise coordination of skeletal muscles. It involves flexion, which bends the arm, and extension, which straightens it.
Flexion and extension showcase different muscle roles in the biceps and triceps. When you bend your arm, the biceps contract to pull the forearm up, while the triceps relax. This movement is essential for activities, like bringing food to your mouth.

When extending, as in reaching out or pushing, the triceps contract, and the biceps relax. This allows the arm to straighten and reach outward. These alternating actions occur seamlessly, allowing us to perform everyday tasks efficiently.
Understanding how arm movement works offers insight into the intricate mechanics of our bodies. It reveals the teamwork between muscles and how our movements are not only powered by muscles but are also controlled with precision.