Question 1

In smooth muscle, calcium binds to calmodulin and then activates the enzyme

Accepted Answer

In smooth muscle, calcium binds to calmodulin, forming a complex that activates myosin light-chain kinase (MLCK), which then phosphorylates myosin light chains, facilitating muscle contraction.

Question 2

Which of the following BEST describes the relationship between motor neuron size, motor unit size, and order of recruitment?

Accepted Answer

Large motor neurons are associated with large motor units and are typically recruited last according to the size principle, which states that smaller motor units are recruited first.

Question 3

The fundamental repeating unit of the myofibril, called a _, gives skeletal muscle its striated appearance and is bordered by _.

Accepted Answer

The sarcomere is the fundamental repeating unit of a myofibril and is bordered by Z lines, which give skeletal muscle its striated appearance.

Question 4

Which of the following could cause a pacemaker potential?

Accepted Answer

The pacemaker potential is primarily caused by the spontaneous opening of sodium channels, which leads to a gradual depolarization of the cell membrane in pacemaker cells.

Question 5

During skeletal muscle contraction, multiple crossbridge cycles are occurring between the same thick and thin filament. Which of the following best describes this process?

Accepted Answer

Crossbridge cycling is asynchronous between a certain thick and thin filament to ensure smooth and continuous muscle contraction without interruption.

Question 6

What causes some muscle fibers to appear red and dark?

Accepted Answer

The answer of What causes some muscle fibers to appear...

Question 7

Which is the longest phase of a twitch?

Accepted Answer

The relaxation phase is the longest phase of a muscle twitch, as it takes time for the muscle fibers to return to their resting state after contraction.

Question 8

The interaction between actin and myosin in smooth muscle requires

Accepted Answer

In smooth muscle, the calcium-calmodulin complex activates myosin light-chain kinase, which then phosphorylates the myosin light chain, allowing myosin to bind with actin.

Question 9

The repeated, oscillating interaction between actin and myosin which results in the generation of force by a skeletal muscle cell is called what?

Accepted Answer

Crossbridge cycling refers to the repeated interaction between actin and myosin filaments, where myosin heads bind to actin, pull, release, and then reattach, leading to muscle contraction.

Question 10

Which of the following is a structural protein that extends along each thick filament from M line to Z line?

Accepted Answer

Titin is a structural protein that extends along each thick filament from the M line to the Z line, providing elasticity and stability to the muscle fiber.

Question 11

Troponin is a complex of three proteins that bind to tropomyosin, calcium, and

Accepted Answer

Troponin is a complex of three proteins that bind to tropomyosin, calcium, and actin.

Question 12

Where are gap junctions commonly found?

Accepted Answer

Gap junctions are found in both single-unit smooth muscle and cardiac muscle. They are important for allowing rapid and coordinated signaling between cells in these tissues. Gap junctions are not typically found in multi-unit smooth muscle, which functions more independently.

Question 13

Which of the following is the voltage sensor that initiates an increase in cytoplasmic calcium in response to an action potential?

Accepted Answer

The dihydropyridine receptor (DHPR) acts as a voltage sensor in muscle cells, detecting the action potential and triggering the release of calcium from the sarcoplasmic reticulum by interacting with the ryanodine receptor.

Question 14

Calcium binding to calmodulin causes phosphorylation by myosin light chain kinase of what protein in what type of muscle?

Accepted Answer

Calcium binding to calmodulin activates myosin light chain kinase, which then phosphorylates myosin in smooth muscle, leading to muscle contraction. This mechanism is specific to smooth muscle.

Question 15

Which type of skeletal muscle fiber has most of its energy come from substrate- level phosphorylation?

Accepted Answer

Glycolytic muscle fibers primarily rely on substrate-level phosphorylation for energy, as they break down glucose anaerobically to produce ATP quickly.

Question 16

The mechanism responsible for the size principle involves

Accepted Answer

The size principle states that smaller motor neurons, which innervate fewer muscle cells, reach threshold and are recruited before larger motor neurons.

Question 17

Which of the following is the correct order of muscle fiber recruitment, from first to last?

Accepted Answer

Muscle fibers are recruited based on the size principle, starting with slow oxidative fibers for endurance and low-intensity activities, followed by fast oxidative fibers for moderate activities, and finally fast glycolytic fibers for high-intensity, short-duration activities.

Question 18

What molecule, present primarily within oxidative skeletal muscle cells, acts as an oxygen buffer due to its ability to bind oxygen?

Accepted Answer

Myoglobin is a molecule found in muscle tissues that binds oxygen, allowing it to act as an oxygen buffer, particularly in oxidative skeletal muscle cells.

Question 19

Which of the following does NOT influence the force generated by an individual muscle fiber?

Accepted Answer

Recruitment refers to the activation of additional muscle fibers or motor units, not the force generated by an individual muscle fiber.

Question 20

The shortening of a skeletal muscle fiber during contraction involves which of the following?

Accepted Answer

During muscle contraction, the sarcomeres shorten as the actin (thin) filaments slide past the myosin (thick) filaments, but the filaments themselves do not shorten. The Z lines move closer together, and the A bands remain the same length.

Quiz 12: Muscle Physiology