As a muscle contracts,
A) it creates energy.
B) the myofibrils break down.
C) the sarcomeres extend.
D) the Z discs move closer together.

Question

Quizplus · Accepted Answer

During muscle contraction, the thin filaments (actin) slide past the thick filaments (myosin), causing the sarcomeres (the repeating units of actin and myosin) to shorten. As a result, the Z discs move closer together, which is responsible for the shortening of the muscle. Therefore, option D is the correct choice. Option A is incorrect because muscle contraction doesn't create energy, but it does consume it. Option B is incorrect because myofibrils are not broken down during muscle contraction. Option C is incorrect because the sarcomeres do not extend during muscle contraction, but rather they shorten.

As a Muscle Contracts