Deck 12: Skeletal Muscle Physiology

Question 1

Stretching a skeletal muscle beyond rest length reduces the force of contraction because of:

A)Increased Ca⁺⁺ sensitivity of actin-myosin interaction.
B)Increased Ca⁺⁺ influx through stretch-activated channels.
C)Decreased actin-myosin overlap.
D)Decreased Ca⁺⁺ uptake by the SR.
E)Decreased intracellular pH.

Answer 1

C

Question 2

Relaxation of skeletal muscle after contraction requires:

A)Ca⁺⁺ release by the ryanodine receptor.
B)Ca⁺⁺ uptake by sarcoplasmic endoplasmic reticulum calcium-adenosine triphosphatase (SERCA).
C)Ca⁺⁺ efflux by the plasmalemmal Ca⁺⁺ pump.
D)Dephosphorylation of a myosin light chain.
E)Activation of Rho kinase.

Answer 2

B

Question 3

The speed of contraction of skeletal muscle is related to:

A)The oxidative capacity of the skeletal muscle fiber.
B)The myosin adenosine triphosphatase (ATPase)activity of the skeletal muscle fiber.
C)The level of β-adrenergic stimulation.
D)The rate of Ca⁺⁺ extrusion from the skeletal muscle fiber.
E)The level of myosin light-chain phosphorylation within the muscle fiber.

Answer 3

B

Question 4

Malignant hyperthermia is a hereditary disorder that can increase surgical risk because temperature may be elevated during certain types of anesthesia.The cause of the increased temperature is an increase in cytosolic Ca⁺⁺ level as a result of an anesthetic-induced:

A)Increase in Ca⁺⁺ release from the SR,as a result of a mutation in the ryanodine receptor.
B)Decrease in Ca⁺⁺ uptake by the SR,as a result of a mutation in SERCA.
C)Increase in frequency of the rupturing of skeletal muscle fibers.
D)Decrease in Ca⁺⁺ extrusion,as a result of hyperphosphorylation of the plasmalemmal Ca⁺⁺ pump.
E)Increase in Ca⁺⁺ influx,as a result of a mutation in N-type Ca⁺⁺ channels.

Question 5

The ability to develop increasing levels of force in an intact muscle composed of both fast- and slow-twitch muscle fibers typically involves:

A)Recruitment of slow-twitch muscle fibers before fast-twitch muscle fibers.
B)Tetany of fast-twitch muscle fibers at lower stimulus frequencies than those for tetany of slow-twitch muscle fibers.
C)A progressive recruitment of more muscle fibers within a given motor unit.
D)A progressive increase in the amplitude of the intracellular Ca⁺⁺ transient.
E)A progressive decrease in the threshold for an action potential in the skeletal muscle.

Question 6

Endurance training typically increases:

A)Ca⁺⁺ influx into the muscle fiber.
B)The oxidative capacity of the muscle.
C)The conversion of slow-twitch muscle fibers into fast-twitch muscle fibers.
D)The number of muscle fibers within a muscle.
E)Ca⁺⁺ extrusion from the muscle fiber.

Question 7

The force of contraction of skeletal muscle can be increased by:

A)Activation of additional skeletal muscle fibers within a motor unit.
B)Increase in the frequency of action potentials within a skeletal muscle fiber.
C)Increase in β-adrenergic stimulation of the skeletal muscle.
D)Increase in myosin light chain phosphorylation in the skeletal muscle.
E)Increase in Ca⁺⁺ extrusion from the skeletal muscle fiber.

Question 8

In the absence of extracellular Ca⁺⁺,an action potential in a motor neuron fails to initiate contraction of the innervated skeletal muscle because of:

A)Inhibition of Ca⁺⁺ influx into the innervated muscle.
B)Inhibition of acetylcholine (ACh)binding to receptors on the muscle end plate.
C)Stimulation of ACh degradation.
D)Inhibition of ACh release from the motor neuron.
E)Inhibition of Ca⁺⁺ binding to troponin C in the innervated muscle.

Question 9

During intense exercise,fatigue of skeletal muscle occurs because of:

A)Depletion of ATP within the skeletal muscle fiber.
B)Ca⁺⁺ overload by mitochondria within the muscle fiber.
C)Inhibition of actin-myosin interaction.
D)Stimulation of Ca⁺⁺ release in the sarcoplasmic reticulum (SR)
E)Increase in pH within the muscle fiber.