Question

The sliding filament mechanism describes the process during which: a. actin and myosin slide relative to each other b. sarcomeres slide relative to each other c. troponin and tropomyosin slide relative to each other d. muscle fibers slide past each other

Short answer

a. actin and myosin slide relative to each other

Step-by-step solution

- Understand the Sliding Filament Mechanism

The sliding filament mechanism refers to the way muscles contract to produce force. It involves the interaction between actin and myosin filaments within the muscle sarcomere.

- Analyze the Provided Options

Examine each option to see which one accurately describes the process of filaments sliding relative to each other during muscle contraction: a) Actin and myosin slide relative to each other b) Sarcomeres slide relative to each other c) Troponin and tropomyosin slide relative to each other d) Muscle fibers slide past each other

- Eliminate Incorrect Options

Through the sliding filament mechanism: b) is incorrect because sarcomeres do not slide; they shorten. c) is incorrect because troponin and tropomyosin move to expose binding sites but do not slide past each other. d) is incorrect because muscle fibers themselves do not slide relative to each other.

- Confirm the Correct Answer

Given the above analysis, the correct answer is: a) Actin and myosin slide relative to each other during muscle contraction, leading to the shortening of the muscle fiber.

Key concepts

Actin

Actin is a vital protein in muscle contraction. It forms thin filaments within the muscle sarcomere. These filaments interact with myosin to enable the sliding filament mechanism. Actin is known for binding sites that, when exposed, allow myosin heads to attach and pull. This interaction is essential for muscle contraction and movement.
Actin works together with regulatory proteins like troponin and tropomyosin. Troponin binds to calcium ions and moves tropomyosin away from actin's binding sites during muscle activation. This exposure allows the cross-bridge formation with myosin, enabling muscle contraction.

• Thin filament in the muscle sarcomere
• Has binding sites for myosin
• Works with troponin and tropomyosin

Myosin

Myosin is a motor protein that plays a critical role in muscle contraction. It forms thick filaments in the sarcomere and has heads that interact with actin. These heads attach to the actin filaments to form cross-bridges, pulling them to slide past each other. This process is called the power stroke.
Myosin heads pivot to shorten the sarcomere, generating muscle contraction. They use energy from ATP to detach, reposition, and attach again to a new binding site on actin, repeating the cycle. This continuous movement results in the sliding filament mechanism.

• Thick filament in the muscle sarcomere
• Interacts with actin through its heads
• Uses ATP for the contraction cycle

Muscle Contraction

Muscle contraction is the process that leads to movement and force generation. It is driven by the sliding filament mechanism where actin and myosin filaments within the sarcomere slide past each other. The process starts with a signal from the nervous system, triggering the release of calcium ions in the muscle fibers.
Calcium binds to troponin, causing a shape change that moves tropomyosin away from actin's binding sites. Myosin heads then attach to actin, forming cross-bridges. Using energy from ATP, myosin pulls actin inward, shortening the sarcomere and contracting the muscle.

• Starts with a nervous signal and calcium release
• Involves actin-myosin interaction
• Shortens the sarcomere to generate movement

Sarcomere

The sarcomere is the fundamental unit of muscle contraction. It is a highly organized structure within muscle fibers, containing repeating patterns of actin (thin) and myosin (thick) filaments. These filaments are arranged in a way that allows them to slide past each other during muscle contraction.
The boundaries of each sarcomere are defined by Z-lines, to which actin filaments are attached. Myosin filaments are located in the center and extend towards the actin. As myosin pulls on the actin filaments, the sarcomere shortens, causing muscle contraction. This shortening is crucial for all muscle movements.

• Basic unit of muscle contraction
• Contains actin and myosin filaments
• Bounded by Z-lines