Question

As ADP and ? are released from a myosin head, a. actin filaments move toward the H zone. b. myosin cross-bridges pull the thin filaments. c. a sarcomere shortens. d. Only a and care correct. e. All of these are correct.

Short answer

(Pi) are released from a myosin head, actin filaments move towards the H zone (statement a), myosin cross-bridges pull the thin filaments (statement b), and a sarcomere shortens (statement c).

Step-by-step solution

Understand the mechanism of muscle contraction

In order to answer this question, it's important to first understand how muscle contraction works. Muscle contraction occurs through the process of the sliding filament theory, where the thick myosin filaments pull the thin actin filaments towards the center (H zone) of a sarcomere. This filament sliding is facilitated by the formation and breaking of myosin cross-bridges which attach to actin and generate force to pull actin filaments.

Analyze statement a: actin filaments move towards the H zone

When ADP and ? (Pi) is released from the myosin head, it generates enough force to move the actin filaments towards the H zone within the sarcomere, which is the space between the two sets of thick filaments. Therefore, statement a is true.

Analyze statement b: myosin cross-bridges pull the thin filaments

The release of ADP and ? is part of the process where myosin cross-bridges form and generate force to pull the thin actin filaments. The myosin head binds to an actin filament, then the release of ADP and ? causes the myosin head to change shape, which generates force and pulls the actin filament. Therefore, statement b is true.

Analyze statement c: a sarcomere shortens

A sarcomere is the functional unit of muscle contraction and consists of overlapping actin and myosin filaments. As the actin filaments are pulled towards the H zone by the myosin cross-bridges, the entire sarcomere shortens, leading to muscle contraction. Therefore, statement c is true.

Determine the correct answer choice

Since all of the given statements (a, b, and c) are true, the correct answer choice is e. All of these are correct.