Question

Which of the following best describes muscular movement at a molecular level?

A) Muscles contract when stimulated.
B) Muscles have local electrical charges that are capable of moving along the muscle fiber.
C) Muscles only pull; they cannot push.
D) Muscles can stretch when needed.

Answer 1

Muscle fibers contract when myosin filaments pull actin filaments closer together, shortening sarcomeres within the muscle fiber. This contraction is facilitated by the neurotransmitter acetylcholine and the presence of calcium ions.

Step-by-step explanation:

According to the sliding filament theory, muscle fibers contract when myosin filaments pull actin filaments closer together, shortening sarcomeres within the muscle fiber. When muscles relax, the sarcomeres extend back to their original position. Muscle contraction is facilitated by the neurotransmitter acetylcholine (ACh) and requires the presence of calcium ions (Ca2+).