Question 1

ATP expenditure is required for both contraction and relaxation of a muscle fibre.

Accepted Answer

During contraction, ATP is required to release myosin heads from actin and to reset the myosin heads for the next round of crossbridge cycling. During relaxation, ATP is required to pump calcium ions back into the sarcoplasmic reticulum, which allows for the muscle fibre to fully relax.

Question 2

More tension is developed during twitch summation than during a single twitch because the duration of elevated cytosolic Ca²⁺ concentration increases during summation,thus increasing the availability of cross-bridge binding sites.

Accepted Answer

During twitch summation, multiple action potentials are generated in rapid succession, resulting in the release of additional Ca²⁺ ions from the sarcoplasmic reticulum. This results in a longer duration of elevated cytosolic Ca²⁺ concentration, which allows for more cross-bridge binding and therefore increases tension development in the muscle fibers.

Question 3

The contraction phase of a muscle cell lasts longer than the relaxation phase.

Accepted Answer

The relaxation phase of a muscle cell lasts longer than the contraction phase. This allows for the muscle to return to its original length before contracting again.

Question 4

The actin filaments in sarcomere contain cross bridges.

Accepted Answer

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Question 5

According to the sliding filament mechanism of muscle contraction,the thick filaments slide in closer together to shorten the sarcomere.

Accepted Answer

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Question 6

Myosin has ATPase activity.

Accepted Answer

Myosin is an enzyme that is involved in muscle contraction and has ATPase activity, which means it can hydrolyze ATP to release energy.

Question 7

The T tubule ranges transversely to the surface of the muscle cell membrane.

Accepted Answer

The T tubule is a structure that extends transversely (perpendicular) to the surface of the muscle cell membrane, allowing for rapid transmission of electrical signals (action potentials) throughout the muscle fiber.

Question 8

Thin and thick filaments overlap in the A band.

Accepted Answer

Thin and thick filaments overlap in the A band of a sarcomere in a muscle fiber. This creates the dark band that is seen under a microscope during muscle contraction.

Question 9

The functional unit of skeletal muscle is the myofibril.

Accepted Answer

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Question 10

Foot proteins link the actin molecules together within a thin filament.

Accepted Answer

The answer of Foot proteins link the actin molecules together...

Question 11

Rigor mortis occurs when Ca²⁺ links actin and the myosin globular head together in a rigor complex.

Accepted Answer

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Question 12

Cross bridges have actin binding sites that are normally covered by troponin and tropomyosin except during excitation-contraction coupling.

Accepted Answer

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Question 13

In order for relaxation to occur,ACh must be removed from the muscle cell's receptors.

Accepted Answer

In order for the muscle to relax, the neurotransmitter ACh must be removed from the receptors on the muscle cell. This happens through the action of enzymes that break down ACh or transport proteins that remove it from the synaptic cleft.

Question 14

During the power stroke,all of the cross bridges on myosin do not stroke in unison when pulling the actin filaments.

Accepted Answer

During the power stroke, cross bridges on myosin pull on individual actin subunits, and not all of them stroke in unison. This creates a sliding movement of the actin filaments relative to the myosin filaments, resulting in muscle contraction.

Question 15

Myosin is considered to be a regulatory protein because it plays an important role in the regulation of muscle contraction.

Accepted Answer

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Question 16

Tropomyosin covers the cross-bridge binding sites on the thick filaments when a sarcomere is not contracting.

Accepted Answer

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Question 17

Acetylcholinesterase removes ACh from receptors.

Accepted Answer

Acetylcholinesterase is an enzyme that breaks down and removes acetylcholine from the synaptic cleft, thereby terminating its effect on the receptors.

Question 18

According to the sliding filament mechanism of muscle contraction,the muscle fibres of one motor unit slide in closer together between the muscle fibres of adjacent motor units.

Accepted Answer

The sliding filament mechanism of muscle contraction describes how thin and thick filaments within a muscle fibre slide past each other to create muscle contractions. It does not involve the sliding of muscle fibres between motor units. Motor units are comprised of a single motor neuron and the muscle fibres it innervates, and they work together to produce coordinated muscle contractions.

Question 19

Muscle relaxation does not take place until all of the ATP is used up.

Accepted Answer

Muscle relaxation is actually triggered by the release of calcium ions and the subsequent reuptake of those ions back into the sarcoplasmic reticulum. ATP is necessary for muscle contraction, but not for relaxation.

Question 20

During muscle contraction,the A band becomes shorter.

Accepted Answer

During muscle contraction, the A band remains the same length while the I band and H zone become shorter.

Quiz 6: Muscle Physiology