muscular system (Chapter 9)

If a biopsy of the quadriceps (thigh extensor) muscles were taken from gold medal-winning speed skaters in the 5 events below, which would most likely have the SMALLEST percentage of type I muscle fibers?

10,000 meters

Which of the following statements about different kinds of skeletal-muscle fibers is TRUE?

A fast-glycolytic fiber can generate greater tension than a slow-oxidative fiber.

Which of the following statements regarding skeletal muscle is TRUE?

A given skeletal muscle fiber will contract if excitatory synaptic inputs sufficiently exceed inhibitory synaptic inputs on the motor neuron that innervates that fiber and the motor neuron fires an action potential.

Binding of ____ to myosin permits cross-bridge ____ between actin and myosin in skeletal muscle cells.

ATP; Detachment

Which of the following statements regarding the motor end plate of a skeletal-muscle fiber is TRUE?

Acetylcholinesterase in the end plate membrane catalyzes the breakdown of acetylcholine.

Which of the following statements is TRUE regarding skeletal-muscle contraction?

Binding of myosin to actin takes place when [Ca2+] increases in the cytosol.

Which membrane protein transport process plays an important role in terminating the contraction of cardiac muscle?

Ca2+-ATPase pumps move Ca2+ from the cytosol back into the sarcoplasmic reticulum.

Which is a TRUE statement about excitation-contraction coupling?

Calcium-induced calcium-release plays a role in cardiac muscle cells, as well as in some smooth muscle cells.

Which of the following statements is FALSE?

Contractile activity of smooth-muscle cells does not normally require Ca2+.

Which of the following statements regarding contraction of a skeletal-muscle fiber is true?

Contracting muscle fibers do not always shorten

Which of the following statements regarding skeletal-muscle contraction is true?

During every muscle contraction, tension is developed in the muscle.

How is the length of a skeletal muscle cell related to the force it can generate?

Skeletal muscle cells generate the most force when the contraction occurs at an intermediate length.

In the first few seconds of skeletal muscle contraction, what is the main mechanism by which ATP is replenished?

Energy and phosphate are transferred from creatine phosphate to ADP.

Why does breathing continue to be rapid and deep for a time after heavy exercise?

Extra oxygen is needed to restore eliminate lactic acid and restore muscle creatine phosphate and glucose concentrations.

Fast-glycolytic muscle fibers differ from slow-oxidative fibers in that:

Fast-oxidative fibers can generate greater maximal tension than slow-oxidative fibers.

During concentric isotonic contraction of a skeletal-muscle fiber, which of these occurs?

I bands shorten

Which of the following statements regarding contraction in skeletal and smooth muscle is TRUE?

In skeletal muscle, calcium initiates contraction by binding to troponin, while in smooth muscle calcium initiates contraction by binding to calmodulin.

which best describes a "myofibril"?

It is a cylindrical organelle composed of myofilaments

How does the chemical curare affect skeletal muscle function?

It is a nicotinic acetylcholine antagonist that blocks synaptic transmission at the neuromuscular junction.

John is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Jim is a marathon runner who specializes in long, steady runs. Compared to John's muscles, how are Jim's most likely to differ?

Jim's muscles will have more mitochondria in his type I and II a muscle fibers.

What is the mechanism by which muscle fatigue causes action potential conduction failure in skeletal muscle cells?

K+ buildup in the T-tubules depolarizes the local resting membrane potential and inactivates Na+ channels.

Which best describes "rigor mortis?"

Lack of ATP following death causes cross-bridges to remain tightly bound to actin.

What is the best description of a tetanic contraction in a skeletal muscle cell?

Multiple action potentials in the motor neuron causes a sustained contraction.

What protein is the principle component of skeletal muscle thick filaments?

Myosin

Which of the following statements regarding myosin in skeletal muscle is TRUE?

Myosin is an ATPase.

Which of these is a major difference between smooth muscle and skeletal muscle?

Myosin is the main regulatory protein in smooth muscle.

Which of these occurs during an isometric contraction of a skeletal muscle?

Sarcomere length does not change.

Which is a TRUE statement about smooth muscle?

Smooth muscle does not use troponin-tropomyosin to regulate cross-bridge activity.

The removal of calcium ions from the cytosol of skeletal muscle causes

The myosin binding sites on actin to be covered by tropomyosin

Which of the following statements regarding whole-muscle contraction is TRUE?

The order of recruitment of motor units in a muscle is such that the last units recruited are those that fatigue most readily.

What is the function of the transverse tubules in a skeletal-muscle fiber?

They allow action potentials to propagate deep into the center of skeletal muscle cells.

Which best describes a role of L-type Ca2+ channels in cardiac muscle cells?

They are responsible for preventing tetanic contractions.

Which of the following does NOT correctly describe cardiac muscle cells?

They can contract in the absence of external calcium.

Which of the following is FALSE regarding single-unit smooth-muscle cells?

They have an individual neuron innervating of each individual smooth-muscle cell.

Compared to type I (slow oxidative) skeletal muscle fibers, how are type II b (fast-glycolytic) skeletalmuscle fibers different?

Type II b fibers fatigue more readily.

Myasthenia gravis is an autoimmune disease in which the immune system gradually destroys the receptors for acetylcholine at the neuromuscular junction. Which of the following drugs might initially be useful in treating the symptoms of this disease?

a drug that inhibits acetylcholinesterase

What is the definition of a "motor unit?"

a single motor neuron plus all the muscle fibers it innervates

Which occurs FIRST as a result of ATP binding to myosin?

actin dissociates from from myosin

Myasthenia gravis is a collection of muscle disorders that cause muscle fatigue and weakness. What is the major mechanism?

autoimmune destruction of nicotinic acetylcholine receptors

The prolonged electrical depolarization of cardiac muscle cells that occurs during contraction is due primarily to the persistent influx of what ion?

calcium

Which of the following choices lists a correct sequence of events following the depolarization of transverse tubules in excitation-contraction coupling in cardiac muscle?

calcium ion influx through sarcolemma, calcium release into cytosol, actin and myosin attach, thin myofilaments slide toward the middle of sarcomeres

Which dietary supplement is most likely to contribute to greater skeletal muscle ATP availability in the first few seconds of skeletal muscle contraction?

creatine

Which is NOT thought to be a mechanism causing fatigue during high-intensity, short duration muscle activity?

depletion of ATP in the fiber

Multiunit smooth-muscle cells

generally have individual innervation of each cell.

Which of these would increase the tension generated in a skeletal muscle?

increasing the frequency of firing in alpha motor neurons innervating the muscle

Rigor mortis is caused by:

lack of ATP.

John is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Jim is a marathon runner who specializes in long, steady runs. Compared to Jim, John is likely to have:

legs with a larger diameter.

When a muscle has been repeatedly contracting at a moderate intensity for an extended period of time (more than a few minutes), what is the primary source of ATP?

oxidative phosphorylation

During an isometric twitch in a skeletal muscle:

sarcomeres do not significantly shorten.

The optimal length (Lo) of a skeletal muscle cell is:

the length at which the muscle can generate its maximum tetanic tension.

Which of the following is NOT a determinant of whole-muscle tension?

the proportion of the muscle fibers within each motor unit that are contracting at any given time

An action potential in the motor end plate rapidly spreads to the interior regions of a muscle cell by means of the:

transverse tubules

In skeletal muscle cells, calcium initiates contraction by binding to:

troponin