During skeletal muscle contraction:
Choose one answer.
A. the A and I bands do not change length.
B. cross bridges are formed between myosin and actin.
C. minimal tension can be generated when the muscle is close to its normal resting length.
D. the myofilaments change length.
E. calcium is released from the T tubule
A
The correct answer is B. Cross bridges are formed between myosin and actin during skeletal muscle contraction.
To understand why this is the correct answer, let's break down the process of skeletal muscle contraction.
Skeletal muscle contractions occur when signals from motor neurons stimulate muscle cells (muscle fibers) to contract. The contraction process involves the interaction between two types of protein filaments in the muscle cells: actin and myosin.
Actin and myosin filaments are organized in a repeated pattern along the muscle fiber, forming units called sarcomeres. Sarcomeres are the functional units responsible for muscle contraction.
During muscle contraction, cross bridges are formed between myosin and actin. The cross bridges are formed when the myosin heads (part of the myosin filaments) attach to the actin filaments. This attachment allows the myosin filaments to slide past the actin filaments, causing the muscle to contract.
The other options can be ruled out as follows:
A. The A and I bands do change length during muscle contraction. The A band (dark band) decreases in length, while the I band (light band) also decreases in length.
C. Minimal tension can actually be generated when the muscle is at its resting length. Optimal tension is generated when the muscle fibers are slightly stretched.
D. The myofilaments (actin and myosin) do change length during muscle contraction. They slide past each other, resulting in shortening of the sarcomeres and hence the muscle fibers.
E. Calcium is indeed involved in the process of muscle contraction, but it is not released from the T tubule. Calcium ions are released from the sarcoplasmic reticulum, a specialized membrane system within the muscle cell, to trigger the binding of myosin to actin and initiate muscle contraction.
Therefore, the correct answer is B. Cross bridges are formed between myosin and actin during skeletal muscle contraction.