Question

During the contraction of a vertebrate skeletal muscle fiber, calcium ions

(A) break cross-bridges as a cofactor in hydrolysis of ATP.

(B) bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed.

(C) transmit action potentials from the motor neuron to the muscle fiber.

(D) spread action potentials through the T tubules.

Short answer

(A)The option “break cross-bridge as a cofactor in the hydrolysis of ATP” isincorrect.

(B)The option “binding with troponin, changing its shape so that the myosin-binding sites on actin are exposed” iscorrect.

(C)The option “transmit action potential from the motor neuron to the muscle fiber” isincorrect.

(D)The option “spread action potential through the T tubules” is incorrect.

Step-by-step solution

Vertebrate skeletal muscle fiber

Calcium ion is an essential molecule in muscle contraction. When activated, dihydropyridine receptors trigger the opening of calcium channels on cisterns leads to calcium diffuses in the cytoplasm and increasing calcium.

Explanation of option ‘(A)’

In muscle contraction, the cross-bridge forms, which refers to the formation of myosin and actin within the muscle cell. After this, myosin binds with the ATP at the head region. The binding of myosin develops actin changes the cross-bridge in skeletal muscle fiber.

Thus, during the contraction of vertebrate skeletal muscle fiber, calcium is not responsible for the formation of break cross bridges as a cofactor in the hydrolysis of ATP.

Therefore, the given option is incorrect.

Explanation of option ‘(B)’

Calcium plays the leading role in binding with troponin molecules. After depolarization, the sarcoplasmic reticulum releases calcium ion is responsible for binding to the troponin, and it changes the structure and moves toward the active site of the actin.

Thus, during vertebrate skeletal muscle fiber contraction, calcium ion is responsible for binding with troponin, changing its shape so that the myosin-binding sites on actin are exposed.

Therefore, the given option is correct.

Explanation of option ‘(C)’

The transmission of action potential to the nerve is known as the neuromuscular junction. Synapses occur between the motor neurons and muscle fibers, transmitting action potential to the brain, making contraction of the muscle.

Thus, during the contraction of vertebrate skeletal muscle fiber, calcium ion is not responsible for transmitting action potential from the motor neuron to the muscle fiber cell.

Therefore, the given option is incorrect.

Explanation of option ‘(D)’

T-tubules allow electrical signals into the cell when an action potential is received into muscle through the T-tubules and conducted depolarization of cells. After depolarization in the muscle ATP pathway starts and releases lactic acid.

Thus, during the contraction of vertebrate skeletal muscle fiber, calcium ion is not responsible for spreading action potential through the T-tubules.

Therefore, the given option is incorrect.