Question

Sliding filament theory can be best explained as

• A. actin and myosin filaments do not shorten but rather slide pass each other
• B. when myofilaments slide pass each other, myosin filaments shorten while actin filaments do not shorten
• C. when myofilaments slide pass each other actin filaments shorten while myosin filaments do not shorten
• D. actin and myosin filaments shorten and slide pass each other.

Answer 1

The Correct Option is A

The Sliding Filament Theory is a fundamental concept in understanding how muscle contraction occurs. This theory best explains the mechanism by which muscles produce force and shorten during contraction. Let's explore the reasoning behind the correct answer:

Explanation:

• The Sliding Filament Theory describes how myofibrils, which are comprised of actin and myosin, slide past one another to generate muscle contraction without the filaments themselves changing length.
• In particular, actin (thin filaments) and myosin (thick filaments) interdigitate, and when a muscle contracts, the heads of the myosin filaments form cross-bridges with the actin filaments and pull them closer together by a ratchet-like mechanism.
• Myosin heads pull the actin filaments towards the center of the sarcomere, which shortens the overall length of the muscle fiber, although the lengths of the filaments remain unchanged. This effectively narrows the H-zone and the I-band while the A-band remains constant.

Conclusion:

• The statement "actin and myosin filaments do not shorten but rather slide past each other" correctly reflects the Sliding Filament Theory, because it highlights the unchanging length of these filaments during muscle contraction. This is the process by which muscle contractions are achieved.

Why Other Options are Incorrect:

• When myofilaments slide past each other, myosin filaments shorten while actin filaments do not shorten: This option is incorrect because neither actin nor myosin filaments shorten; they only slide past each other.
• When myofilaments slide past each other actin filaments shorten while myosin filaments do not shorten: This is incorrect for the same reason as above; the individual filaments do not change in length.
• Actin and myosin filaments shorten and slide past each other: This is also incorrect as the filaments maintain their original length while sliding.