Chapter 20 Quiz

. Which statement about skeletal muscle is true?

Proteins in thick filaments pull on thin filaments, while intermediate filaments hold sarcomeres together.

Proteins in thin filaments pull on intermediate filaments, while thick filaments hold sarcomeres together.

Proteins in thin filaments pull on thick filaments, while intermediate filaments hold sarcomeres together.

Proteins in intermediate filaments pull on thin filaments, while thick filaments hold sarcomeres together.

. The power stroke of the myosin head occurs in conjunction with what other event of the cross-bridge cycle?

ATP hydrolysis to ADP and inorganic phosphate

ATP binding to the myosin head

Release of ADP from the myosin head

Release of inorganic phosphate from the myosin head

. In the absence of _______, a muscle can contract but cannot relax.

Ca²⁺

myosin

ATP

oxygen

. In a vertebrate skeletal muscle cell, depolarization of the t-tubule membrane causes dihydropyridine receptors to

open and conduct Ca²⁺ into the t-tubule.

open and conduct Ca²⁺ into the sarcoplasmic reticulum.

change conformation and interact with ryanodine receptors.

bind dihydropyridines and change configuration.

. A hypothetical skeletal muscle cell with no t-tubules would probably

contract and relax more quickly during twitch contractions.

contract and relax more slowly during twitch contractions.

shorten more quickly during tetanic contractions.

have a lower rate of aerobic ATP production.

. During an isometric tetanic contraction, the sarcomeres generate

no force.

force but cannot stretch the elastic component of the muscle.

force and stretch the elastic component of the muscle, but they cannot move the load.

force but do not transmit it to the elastic component of the muscle.

. Why is the latent period of an isotonic twitch different from that of an isometric twitch?

The motoneuron sends a longer action potential if there is an isotonic load on the muscle.

The motoneuron sends a longer action potential if there is an isometric load on the muscle.

An isotonic twitch does not begin until the muscle develops enough force to lift the load.

An isometric twitch does not begin until the muscle develops enough force to lift the load.

. Which of the following factors would increase the stimulation frequency at which a muscle shifts from twitch to tetanic contractions?

Voltage-gated sodium channels with faster kinetics

A larger volume fraction of mitochondria

A larger volume fraction of myofibrils

A larger number of SR Ca²⁺-ATPase proteins

. On the plateau of the length–tension curve,

all myosin heads are in proximity to actin.

all actin monomers are in proximity to myosin heads.

the width of the A band is minimized.

the distance between Z disc is minimized.

. If a muscle contains 10,000 sarcomeres in a series (i.e., end-to-end along its length), each sarcomere is ~2.5 µm in length, and each sarcomere can shorten by 2.5 µm/s, how fast can the muscle shorten?

2.5 µm/s

2.5 mm/s

2.5 cm/s

2.5 m/s

. Muscle A has a volume of 200 cm³, a length of 10 cm, and a cross-sectional area of 20 cm². Muscle B has a volume of 100 cm³, a length of 5 cm, and a cross-sectional area of 20 cm². Which statement about muscles A and B is true?

Both muscles can produce the same power, but they can shorten at different speeds.

Both muscles can shorten at the same speed, but they can produce different amounts of power.

Both muscles can exert the same force and can produce the same amount of power.

Both muscles can exert the same force, but one can shorten more quickly than the other.

. Order the mechanisms of ATP generation by decreasing yield per episode of use.

Creatine phosphate; anaerobic glycolysis; aerobic catabolism

Anaerobic glycolysis; creatine phosphate; aerobic catabolism

Aerobic catabolism; creatine phosphate; anaerobic glycolysis

Aerobic catabolism; anaerobic glycolysis; creatine phosphate

. Which statement about slow oxidative and fast glycolytic muscle fibers is false?

Their thick and thin filaments are arranged differently.

They have different numbers of organelles such as mitochondria and sarcoplasmic reticulum.

They have different amounts of metabolic enzymes such as hexokinase or citrate synthase.

They have different amounts of certain excitation–contraction coupling proteins, such as SR Ca²⁺-ATPase.

. Which best explains why fast glycolytic muscle fibers are larger than slow oxidative fibers?

Slow oxidative fibers rely on the diffusion of oxygen via capillaries.

Slow oxidative fibers can oxidize a variety of fuels, whereas fast glycolytic fibers primarily oxidize glucose/glycogen.

Fast glycolytic fibers are larger to generate larger action potentials and greater force.

Fast glycolytic fibers are larger to exchange glucose across the sarcolemma more quickly.

. Slow oxidative fibers in skeletal muscle are used

only for motions requiring maximum power output, such as jumping.

constantly, for postural activities such as standing and sitting.

intermittently, for activities requiring more force output than the fast glycolytic fibers alone can produce.

intermittently, for activities requiring more force output than the fast glycolytic and fast oxidative glycolytic fibers alone can produce.

. Compared to a typical avian leg muscle, hummingbird flight muscle

produces more force per cross-sectional area.

has an exceptionally high volume fraction of mitochondria.

has very high numbers of muscle fibers per capillary.

has very high levels of SR Ca²⁺-ATPase, but low levels of mitochondria.

. Muscles of the larynx that help mammals to produce complex sounds can contract and relax at much higher frequencies than the muscles of the limbs, but they produce relatively low force as they act on the vocal cords. Based on these characteristics, one would predict that laryngeal muscles have

high levels of myosin.

high levels of parvalbumin.

high levels of troponin T.

unusually long sarcomeres.

. Calcium enters the cytoplasm of a smooth muscle cell by

active transport from the sarcoplasmic reticulum only.

active transport from the extracellular space and the sarcoplasmic reticulum.

diffusion from the sarcoplasmic reticulum only.

diffusion from the extracellular space and the sarcoplasmic reticulum.

. Which of the following cannot modulate force production in smooth muscle?

Inhibition of myosin light-chain kinase

Inhibition of myosin light-chain phosphatase

Binding of Ca²⁺ to troponin C

Hormonal stimuli

. In smooth muscle, calcium must bind to _______ to initiate contraction.

calmodulin

troponin C

myosin

ryanodine receptor

Chapter 20 Quiz

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