Deck 9: Muscle

Question 1

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

A)actin
B)myosin
C)troponin
D)calmodulin
E)tropomyosin

Answer 1

B

Question 2

Which best describes "rigor mortis?"

A)Lack of ATP following death causes cross-bridges to remain tightly bound to actin.
B)Lack of ATP following death causes calcium to remain in the cytosol,continuously stimulating cross-bridge cycling.
C)Repeated,high-frequency action potentials to a skeletal muscle fiber causes sustained contraction following death.
D)Following death,calcium-activated proteases degrade all proteins in skeletal muscle fibers,making muscles limp.
E)Build-up of K+ in T-tubules causes constant,tetanic contractions of skeletal muscles that last for about 12 hours following death.

Answer 2

A

Question 3

Rigor mortis is caused by:

A)buildup of lactic acid.
B)lack of Ca²⁺.
C)depletion of glycogen.
D)lack of ATP.
E)deficient acetylcholine receptors.

Answer 3

D

Question 4

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

A)They store the calcium ions that are the main source of activation for the cross-bridge cycle.
B)They form the Z lines that mark the end of each sarcomere.
C)They allow action potentials to propagate deep into the center of skeletal muscle cells.
D)They manufacture and store ATP.
E)They run in parallel with the myofibrils,and have abundant Ca²⁺-ATPase proteins for pumping Ca²⁺ back into the sarcoplasmic reticulum.

Question 5

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

A)tropomyosin.
B)actin.
C)troponin.
D)myosin.
E)the thick filament.

Question 6

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

A)Only one cross-bridge cycle can occur when the [Ca²⁺] is elevated in the cytosol; in order to undergo a second cycle,[Ca²⁺] must be sequestered in the sarcoplasmic reticulum and released again.
B)ATP hydrolysis products must be removed from myosin before it can bind to actin.
C)Binding of myosin to actin takes place when [Ca²⁺] increases in the cytosol.
D)A single twitch in skeletal muscle lasts the same length of time as the action potential that causes it.
E)The powerstroke of the cross-bridge cycle occurs simultaneously with ATP being hydrolyzed into ADP and P_i.

Question 7

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

A)Z lines.
B)sarcoplasmic reticulum.
C)H zone.
D)transverse tubules.
E)pores in the plasma membrane.

Question 8

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

A)cross-bridge heads are cocked into an "energized" state
B)actin dissociates from from myosin
C)Ca²⁺ is released from the sarcoplasmic reticulum
D)actin binds to myosin
E)cross-bridges rotate,sliding past the thin filament

Question 9

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

A)ATP; attachment
B)ATP; detachment
C) calcium; attachment
D) calcium; detachment
E) actin; detachment

Question 10

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

A)sarcomeres lengthen
B)A bands shorten
C)I bands shorten
D)A bands lengthen
E)thin filaments shorten

Question 11

What is the definition of a "motor unit?"

A)a single motor neuron plus all the muscle fibers it innervates
B)a single muscle fiber plus all of the motor neurons that innervate it
C)all of the motor neurons supplying a single muscle
D)a pair of antagonistic muscles
E)all of the muscles that affect the movement of any given joint

Question 12

How does the chemical curare affect skeletal muscle function?

A)It activates an autoimmune disease that destroys myelin.
B)It blocks the action of acetylcholinesterase at the neuromuscular junction.
C)It is a muscarinic acetylcholine receptor antagonist that blocks synaptic transmission at the neuromuscular junction.
D)It is a nicotinic acetylcholine antagonist that blocks synaptic transmission at the neuromuscular junction.
E)It locks ligand-gated channels in the open state,leading to spastic contractions of muscle.

Question 13

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

A)Thick filaments shorten when muscle cells contract.
B)Some contractions occur without cross-bridge activation.
C)Contracting muscle fibers do not always shorten.
D)Contraction does not always require the occurrence of an action potential.
E)Contraction only occurs following summation of action potentials from many motor neurons.

Question 14

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

A)During a lengthening contraction,the tension exerted by the muscle exceeds the load on the muscle.
B)In every isotonic muscle contraction,the length of the muscle remains constant.
C)During every muscle contraction,muscle fibers change length.
D)During every muscle contraction,tension is developed in the muscle.
E)Cross-bridges cycle faster during isometric contractions than during isotonic contractions.

Question 15

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

A)The I bands shorten and the A bands stay the same length.
B)The thick and thin filaments slide past each other.
C)Sarcomere length does not change.
D)The A bands shorten and the I bands stay the same length.
E)Cross-bridges lock onto actin,similar to what occurs in rigor mortis.

Question 16

During an isometric twitch in a skeletal muscle:

A)tension generated by the muscle always exceeds the load on the muscle.
B)tetanus occurs.
C)sarcomeres do not significantly shorten.
D)the whole muscle shortens.
E)the load on the muscle is always greater than the tension generated.

Question 17

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

A)Muscarinic receptors in the end plate are activated by binding to acetylcholine.
B)Temporal summation of multiple end plate potentials is required in order to trigger an action potential in the muscle-fiber membrane.
C)Acetylcholinesterase in the end plate membrane catalyzes the breakdown of acetylcholine.
D)Sympathetic nerve fibers terminate on skeletal muscle fibers at the motor end plate.
E)The motor end-plate under the axon terminal contains a large number of voltage-gated Na⁺ channels.

Question 18

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

A) the myosin binding sites on actin to be uncovered by tropomyosin.
B) tropomyosin to change conformation and thereby move troponin molecules over cross-bridge binding sites.
C) troponin to change conformation and thereby expose cross-bridge binding sites.
D) the myosin binding sites on actin to be covered by tropomyosin.
E) None of the choices are correct.

Question 19

Which best describes a "myofibril?"

A)It is a single skeletal-muscle cell.
B)It is a cylindrical cellular organelle composed of myofilaments.
C)It is a hollow membranous structure that stores calcium.
D)It is composed of a single type of protein and forms cross-bridges.
E)It is a fibrous junction between a muscle cell and a tendon.

Question 20

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)a drug that inhibits acetylcholinesterase
B)a drug that inhibits release of acetylcholine
C)curare
D)atropine (a muscarinic acetylcholine receptor antagonist)
E)a nicotinic acetylcholine receptor antagonist

Question 21

Which of the following statements regarding skeletal muscle is TRUE?

A)Skeletal muscle fibers have pacemaker activity.
B)Skeletal muscle fibers are joined together by gap junctions.
C)A given skeletal muscle fiber will contract when excitatory nervous stimuli sufficiently exceed inhibitory nervous stimuli at the motor end plate
D)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.
E)Skeletal muscle contraction is inhibited by inhibitory motor neurons that synapse onto skeletal muscle fibers.

Question 22

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

A)The tension in a skeletal muscle cell is greatest when contractions occur at either very short or very long lengths.
B)Skeletal muscle cells generate the same amount of force,regardless of their length.
C)The shorter a skeletal muscle cell is when it begins to contract,the stronger the force generation will be.
D)The longer a skeletal muscle cell is when it begins to contract,the stronger the force generation will be.
E)Skeletal muscle cells generate the most force when the contraction occurs at an intermediate length.

Question 23

Why does breathing continue to be rapid and deep for a time after heavy exercise?
8-7-2013

A) Extra oxygen is needed to eliminate lactic acid and restore muscle creatine phosphate and glucose concentrations.
B)The respiratory system is slow to increase and decrease its function before and after exercise,which is why it takes awhile for breathing to slow down.
C)Lactic acid that builds up during heavy exercise must be exhaled into the air,so heavy breathing must continue for awhile after exercise to eliminate it.
D)The ATP level in muscle cells falls drastically during heavy exercise,and extra oxygen is needed to restore it.
E)The extra ventilation is not needed to replenish energy stores in muscle fibers,but rather simply to restore the blood pH to normal after the production of excess lactic acid during the exercise.

Question 24

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?

A)transfer of energy and phosphate from creatine phosphate to ADP
B)glycolysis
C)oxidative phosphorylation
D)breakdown of myosin
E)uptake of ATP from the blood plasma

Question 25

If a biopsy of the quadriceps (thigh extensor)muscles were taken from gold medal-winning speed skaters in the 4 events below,which would most likely have the SMALLEST percentage of type I muscle fibers?
Rev: 11_02_2012

A)10,000 meters
B)5,000 meters
C)1,000 meters
D)500 meters

Question 26

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:

A)legs with a larger diameter.
B)legs with a smaller diameter.
C)hypertrophy of type I muscle fibers.
D)a higher density of capillaries in his legs.
E)lower concentrations of glycolytic enzymes in his leg muscles.

Question 27

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

A)Myosin is the main regulatory protein in smooth muscle.
B)Myosin is the main regulatory protein in skeletal muscle.
C) Skeletal muscle usually exhibits spontaneous activity,while smooth muscle cannot contract spontaneously.
D)Only skeletal muscle requires increased calcium ion concentration in the cytosol for contraction.
E)Only skeletal muscle has both actin and myosin.

Question 28

Which of the following statements is FALSE?

A)Synaptic input onto skeletal muscle cells is always excitatory,whereas inputs to smooth muscle cells may be either excitatory or inhibitory.
B)A single smooth-muscle cell may be innervated by both a sympathetic neuron and a parasympathetic neuron.
C)Contractile activity of smooth-muscle cells does not normally require Ca²⁺.
D)In the absence of any neural input,skeletal muscle cannot generate tension.
E)Ca²⁺ that activates contraction of smooth muscles can come from either the ECF or from the sarcoplasmic reticulum.

Question 29

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

A)The order of recruitment of motor units in a muscle is such that the last units recruited are those that fatigue most readily.
B)The order of recruitment of motor units in a muscle is such that the first units recruited generate the most tension
C)Motor units whose motor neurons have large-diameter cell bodies are recruited first,while motor units with smaller-diameter motor neurons are only activated as the level of activation in the spinal cord increases.
D)The order of motor unit recruitment is independent of the size of the alpha motor neuron that innervates them.
E)Recruitment of one fast-glycolytic motor unit provides a smaller increment in whole-muscle tension than recruitment of one slow-oxidative motor unit.

Question 30

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

A)Energy and phosphate are transferred from creatine phosphate to ADP.
B)Oxidative phosphorylation rapidly generates ATP from glucose.
C)Glycolysis produces ATP from glycogen.
D)Oxidation of fatty acids into ATP occurs in the mitochondria.
E)Myoglobin catalysis produces ATP.

Question 31

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

A)Myosin cross-bridge heads contain two binding sites,one for actin and one for tropomyosin.
B)Myosin is an ATPase.
C)The rate of ATP hydrolysis by myosin is the same in all types of skeletal muscle.
D)All of the myosin cross-bridge heads in a thick filament are oriented and rotate in the same direction.
E)Troponin covers the binding site on myosin molecules until Ca²⁺ binds to troponin to remove it from its blocking position.

Question 32

Which is a TRUE statement about smooth muscle?

A)Smooth muscle is striated.
B)Smooth muscle does not have thick and thin filaments.
C)Smooth muscle does not use troponin-tropomyosin to regulate cross-bridge activity.
D)Changes in cytosolic calcium do not regulate cross-bridge activity in smooth muscle.
E)The myosin in smooth muscle requires phosphorylation before it can bind to ATP.

Question 33

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

A)A single action potential in the motor neuron causes a sustained contraction.
B) Multiple action potentials in the motor neuron cause a sustained contraction.
C)The action potential in the muscle cell is prolonged to last as long as the contraction.
D)Repeated action potentials from the motor neuron summate into a sustained depolarization of the motor end plate,causing a sustained contraction.
E)A very large amplitude action potential in the motor neuron causes a very strong contraction in the skeletal muscle cell.

Question 34

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

A) fast-glycolytic fibers rely on creatine phosphate as an ATP source for the first few seconds of contraction but
Slow-oxidative fibers do not.
B) fast-glycolytic fibers have a smaller diameter than slow-oxidative fibers.
C) fast-oxidative fibers can generate greater maximal tension than slow-oxidative fibers.
D) fast-oxidative fibers generate less lactic acid than slow-oxidative fibers.

Question 35

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

A)Slow-oxidative fibers have a greater abundance of glycogen than do fast-glycolytic fibers.
B)Fast-glycolytic fibers have a greater abundance of myoglobin than do slow-oxidative fibers.
C)A fast-glycolytic fiber can generate greater tension than a slow-oxidative fiber.
D)Fast-glycolytic fibers and slow-oxidative fibers are innervated by alpha motor neurons of the same diameter.
E)To generate ATP,fast-glycolytic fibers depend mainly on oxidative phosphorylation while slow-oxidative fibers depend mainly on glycolysis.

Question 36

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?

A)Jim's muscles will have more glycogen stored in his type II b muscle fibers.
B)Jim's muscles will have more mitochondria in his type I and II a muscle fibers.
C)Jim's muscles will have less myoglobin in his type I muscle fibers.
D) Jim's type II b fibers will be larger in diameter.
E)Jim will have a greater proportion of type II muscle fibers and a lower proportion of type I fibers than John.

Question 37

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

A)the number of muscle fibers contracting
B)the tension produced by each contracting fiber
C)the numbers of motor units recruited
D)the frequency of motor neuron stimulation
E)the proportion of the muscle fibers within each motor unit that are contracting at any given time

Question 38

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

A)the length at which the muscle can generate its maximum tetanic tension.
B)the shortest length the muscle can achieve while attached to bone,because the amount of overlap between thick and thin filaments is maximal then.
C)generally the length attained when the joint it crosses is fully extended.
D)the only length at which any tension can be generated by the muscle cell.
E)the length at which thin filaments from opposite sides of a sarcomere overlap.

Question 39

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

A)increasing the frequency of firing in alpha motor neurons innervating the muscle
B)stretching the muscle to very long lengths
C)resting the muscle for several weeks
D)switching off fast-glycolytic motor units and activating an equal number of slow-oxidative motor units
E)increasing the amplitude of action potentials in the alpha motor neurons that innervate the muscle

Question 40

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

A)Type II b fibers have more abundant mitochondria.
B)Type II b fibers fatigue more readily.
C)Type II b fibers have more abundant myoglobin.
D)Type II b fibers are smaller in diameter.
E)Type II b motor units contain fewer fibers per alpha motor neuron.

Question 41

Which is a TRUE statement about excitation-contraction coupling?

A)In skeletal muscle cells,it requires the influx of extracellular calcium ion.
B)In smooth muscle cells,it must be preceded by an action potential in the cell membrane.
C)In all kinds of muscle it requires the entry of calcium from the extracellular fluid.
D)Calcium-induced calcium-release plays a role in cardiac muscle cells,as well as in some smooth muscle cells.
E)In skeletal muscle cells,EC coupling begins when an action potential propagates along the sarcoplasmic reticulum membrane.

Question 42

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

A)Ca ²⁺-ATPase pumps move Ca²⁺ from the T-tubule back into the sarcoplasmic reticulum.
B)Na⁺/K⁺-ATPase pumps move Na⁺ back into the cytosol and K⁺ back into the T-tubule lumen.
C)Ca²⁺-ATPase pumps move Ca²⁺ from the cytosol back into the sarcoplasmic reticulum.
D)Na⁺/Ca²⁺-exchangers move Na⁺ out of the cytosol in exchange for Ca²⁺ movement into the sarcoplasmic reticulum.
E)Na⁺/K⁺-ATPase pumps move Na⁺ and K⁺ back out of the cell.

Question 43

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

A)In skeletal muscle,calcium initiates contraction by binding to troponin,while in smooth muscle calcium initiates contraction by binding directly to myosin.
B) In skeletal muscle,calcium ions bind to a regulatory protein on thin filaments; in smooth muscle,calcium ions bind to a regulatory protein on thick filaments.
C)In skeletal muscle,calcium initiates contraction by binding to myosin light-chain kinase,while in smooth muscle calcium initiates contraction by binding directly to tropomyosin.
D)In skeletal muscle,calcium initiates contraction by binding to troponin,while in smooth muscle calcium initiates contraction by binding to calmodulin.
E) All of the choices are true.

Question 44

The binding of ATP to myosin causes an allosteric change in myosin's actin-binding site such that the affinity of myosin for actin is decreased.

Question 45

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

A)overproduction of acetylcholinesterase
B)autoimmune destruction of nicotinic acetylcholine receptors
C)demyelination of axons in motor pathways
D)autoimmune destruction of L-type Ca²⁺ channels.
E)a tumor that overproduces acetylcholine

Question 46

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

A)calcium release into cytosol,calcium ion influx through sarcolemma,actin and myosin attach,thin filaments slide toward the middle of sarcomeres
B)actin and myosin attach,thin filaments slide toward the middle of sarcomeres,calcium release into cytosol
C)calcium release into cytosol,actin and myosin attach,calcium ion influx through sarcolemma,thin myofilaments slide toward the middle of sarcomeres
D)calcium release into cytosol,actin and myosin attach,thin filaments slide toward the middle of sarcomeres,calcium ion influx through sarcolemma
E)calcium ion influx through sarcolemma,calcium release into cytosol,actin and myosin attach,thin myofilaments slide toward the middle of sarcomeres

Question 47

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

A)They function exactly the same in cardiac muscle cells as they do in skeletal muscle.
B)They are directly responsible for making cardiac muscle fatigue resistant.
C)They are responsible for preventing tetanic contractions.
D)They cause the absolute refractory period to be very brief.
E)They act as non-conducting voltage sensors that mediate excitation-contraction coupling.

Question 48

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

A)They have an individual neuron innervating of each individual smooth-muscle cell.
B)They have many gap junctions between cells.
C)They may have pacemaker activity.
D)They may respond to stretch by contracting.
E)They exhibit tone.

Question 49

During concentric contractions of skeletal muscle,the I band and H zone shorten but the A band stays the same.

Question 50

The name given to the repeating functional units that cause striations in a skeletal muscle myofibril is "sarcomere."

Question 51

Actin is an ATPase enzyme.

Question 52

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

A)They are arranged in layers surrounding hollow cavities in the heart.
B)They are much shorter than skeletal muscle fibers,and generally have a single nucleus.
C)Their membranes are depolarized initially by the influx of sodium ions.
D)They depolarize prior to contraction.
E)They can contract in the absence of external calcium.

Question 53

During skeletal-muscle contraction,the distance between the Z lines of a sarcomere decreases because of shortening of the filaments.

Question 54

Multiunit smooth-muscle cells

A)generally have individual innervation of each cell.
B)have many gap junctions between cells.
C)respond to stretch by relaxing.
D)can only be excited,and not inhibited.
E)have abundant T-tubules.

Question 55

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

A)sodium
B)calcium
C)nitrate
D)chloride
E)potassium

Question 56

The step of the cross-bridge cycle that immediately follows the attachment of ATP to the myosin head is referred to as the "powerstroke."

Question 57

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

A)fatty acids
B)sports drinks with electrolytes and mineral spirits
C)sugar
D)protein
E)creatine

Question 58

The energy for muscle contraction is provided indirectly by the hydrolysis of ATP.

Question 59

Skeletal muscles are made up of bundles of muscle fibers attached to bone by connective-tissue called tendons.

Question 60

The force-generating sites in a myofibril are the Z lines.

Question 61

The site of Ca²⁺ storage in muscle cells is the lateral sacs of the transverse tubules.

Question 62

The phenomenon of rigor mortis demonstrates that myosin can remain bound to actin in the absence of additional ATP,but the bond cannot then be broken.

Question 63

"Excitation-contraction coupling" refers to the binding of energized myosin to actin.

Question 64

Endurance exercise,such as long-distance swimming,causes a preferential increase in glycolytic enzymes and increased mass of the exercising muscles.

Question 65

Characteristics of slow-oxidative fibers include numerous mitochondria,abundant myoglobin and large stores of glycogen.

Question 66

The larger the diameter of a skeletal-muscle fiber,the greater the tension it can generate.

Question 67

The fiber type intermediate between the two extremes of fast-glycolytic and slow-oxidative is slow-glycolytic.

Question 68

When the load on a skeletal muscle is less than the tension the muscle generates,a concentric isotonic contraction results.

Question 69

The term "twitch" refers to the mechanical response of a muscle fiber during one cross-bridge cycle.

Question 70

In general,activating a slow-oxidative motor unit in a muscle will generate more tension than activating a fast-glycolytic motor unit.

Question 71

Curare blocks neuromuscular transmission by preventing the release of neurotransmitters from the motor neuron.

Question 72

Binding of myosin to actin in skeletal muscle cells does not normally take place in the absence of Ca²⁺.

Question 73

Fast fibers can be distinguished from slow fibers by the rate at which their myosin-ATPases split ATP.

Question 74

A skeletal muscle generates its greatest twitch tension when it is stretched to twice its resting length.

Question 75

The latent period of an isotonic twitch is shorter than the latent period of an isometric twitch.

Question 76

Muscles used for delicate,finely controlled movements have smaller motor units than muscles used for high power activities.

Question 77

During isometric contraction of a skeletal-muscle fiber,tension increases but the fiber length stays the same.

Question 78

Organophosphate "nerve gases" induce paralysis by blocking neural stimulation of the neuromuscular junctions,while botulinum toxin produces the same effect by inhibiting acetylcholinesterase.

Question 79

The difference in color between white muscle and red muscle is accounted for by the greater abundance of glycogen in white muscle.

Question 80

Sustained contraction and tension in a skeletal muscle is called tetanus.