PHA 404 Human Physiology Ch 9 Skeletal Muscle MC Only

1) 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.

B

2) What protein is the principal component of skeletal muscle thick filaments? A) Actin B) Myosin C) Troponin D) Calmodulin E) Tropomyosin

B

21) Tetanus toxin inhibits acetylcholinesterase activity. What will a person suffering from tetanus toxin poisoning look like? A) All muscles of the body might exhibit frequent small twitches. B) All muscles of the body might present a tense, fully contracted state. C) All muscles of the body might present a limp, relaxed state known as flaccid paralysis. D) All muscles of the body will be completely normal in function.

B

26) 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.

B

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.

B

32) Compared to type 1 (slow oxidative) skeletal muscle fibers, how are type 2X (fast-glycolytic) skeletal muscle fibers different? A) Type 2X fibers have more abundant mitochondria. B) Type 2X fibers fatigue more readily. C) Type 2X fibers have more abundant myoglobin. D) Type 2X fibers are smaller in diameter. E) Type 2X motor units contain fewer fibers per alpha motor neuron.

B

41) Sarah is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Priya is a marathon runner who specializes in long, steady runs. Compared to Sarah's muscles, how are Priya's most likely to differ? A) Priya muscles will have more glycogen stored in her type 2X muscle fibers. B) Priya's muscles will have more mitochondria in her type 1 and 2A muscle fibers. C) Priya's muscles will have less myoglobin in her type 1 muscle fibers. D) Priya's type 2X fibers will be larger in diameter. E) Priya will have a greater proportion of type 2 muscle fibers and a lower proportion of type 1 fibers than Sarah.

B

53) 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

B

57) 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

B

6) 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

B

7) 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 myosin. C) Ca2+ is released from the sarcoplasmic reticulum. D) Actin binds to myosin. E) Cross-bridges rotate, sliding past the thin filament.

B

111) (Select all that apply) Extracellular calcium plays a role in contraction in A) skeletal muscle cells. B) smooth muscle cells. C) cardiac muscle cells. D) None of these types of cells.

B, C

11) In a laboratory experiment you have treated a muscle cell with a calcium channel blocker. The membrane still depolarizes, but the concentration of calcium never increases in the cytosol. Which of the following describes what will happen next? A) Only one cross-bridge cycle will occur but no second cycle. B) Binding of myosin to actin will take place. C) Tropomyosin will continue to cover the myosin binding sites on actin and no cross-bridges will form. D) A single twitch in skeletal muscle but no sustained contraction. E) Contraction will occur, but the muscle will be stuck in the contracted state and unable to relax.

C

14) 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.

C

15) A build-up of K+ in the T-tubules can occur during periods of frequent muscle cell potentials. What will be the result? A) Inhibition of neurotransmitter release from the motor neuron B) Inhibition of muscle cell depolarization and contraction C) Inhibition of relaxation, muscle stays in contracted state D) None of the answer choices are correct

C

19) A scientist labels ACh with fluorescent dye to be able to visualize under the microscope where ACh travels and binds. She takes an image of the motor end plate and see that ACh is A) bound to muscarinic receptors at the end plate. B) inside the muscle cell sarcoplasm. C) bound to acetylcholinesterase in the end plate membrane. D) bound to receptors on the sarcoplasmic reticulum. E) bound to Ca2+ ions.

C

23) 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 significantly. 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.

C

24) 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) H zones shorten.

C

3) 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

C

30) 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

C

34) The muscles in your fingers have a predominance of fast-glycolytic fibers, whereas the muscles of your feet have a predominance of slow-oxidative fibers. Which of the following statements accurately describes their differences? A) The muscle fibers of the feet have a greater abundance of glycogen than do the muscle fibers of the hands. B) Muscle fibers of the feet have a greater abundance of myoglobin than do muscle fibers of the hands. C) Muscle fibers of the hands can generate greater tension than muscle fibers of the feet. D) Muscle fibers in both locations are innervated by alpha motor neurons of the same diameter. E) More oxidative phosphorylation occurs in the hands than the feet.

C

4) 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.

C

43) 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.

C

45) 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.

C

5) In skeletal muscle cells, calcium initiates contraction by binding to A) tropomyosin. B) actin. C) troponin. D) myosin. E) the thick filament.

C

54) You are trying to design a new drug to painlessly euthanize animals. Your plan is to design a molecule that blocks the action of one of the following pumps so that heart muscle stays contracted and blood movement is stopped. Which would be effective? A) Ca 2+-ATPase pumps on the cell membrane B) Na+/K+-ATPase pumps on the cell membrane C) Ca2+-ATPase pumps on the sarcoplasmic reticulum D) Na+/Ca2+-exchangers on the cell membrane E) None of these would result in sustained muscle contraction

C

55) 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.

C

113) (Select all that apply) You are training for a marathon. As you increase your level of physical fitness, you've noticed that the time spent recovering (breathing heavily after stopping running) is decreasing. What change to your muscle cells might account for this? A) Increase in actin concentration B) Increase in muscle size (hypertrophy) C) Increase in myoglobin concentration D) Increase in creatine concentration E) Increase in myosin concentration

C, D

12) 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

A

16) Based on its molecular properties, nicotine will have what effect on skeletal muscle contraction? A) Increases in contraction or contraction is more likely to happen B) Decreases in contraction or contraction is less likely to happen C) Effects on the motor neuron, but not on the muscle tissue itself D) Nicotine has no effect on muscle cells

A

22) 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

A

28) The optimal length (Lo) 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.

A

29) 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.

A

33) Unlike humans, cows eat all day. They spend hours and hours chewing with very little rest from the task in a 24-hour period. The food they eat (grass) is difficult to break down, requiring a lot of chewing. Understanding the endurance required for these chewing muscles, what fiber type would you expect to be predominant in their chewing muscles? A) Type 1 B) Type 2A C) Type 2X D) Type 3 E) There is not enough information to predict a dominant muscle fiber type

A

35) Sarah is a girl with dreams of becoming an Olympic marathon runner. She just learned that she has a rare genetic mutation and does not produce functional creatine phosphate. What portion of Sarah's marathon experience will be effected? A) Just the first few seconds of exercise B) All muscle contractions after Sarah reaches her maximum heart rate (about 10 minutes into her run) C) All muscle contractions after Sarah reaches fatigue (about an hour into her run) D) Every moment of Sarah's runs E) No effects on her running

A

38) 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

A

39) 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.

A

40) Sarah is a sprinter who specializes in quick and powerful bursts of speed followed by periods of rest. Priya is a marathon runner who specializes in long, steady runs. Compared to Priya, Sarah is likely to have A) leg muscles with a larger diameter. B) leg muscles with a smaller diameter. C) hypertrophy of type I muscle fibers. D) a higher density of capillaries in her leg muscles. E) lower concentrations of glycolytic enzymes in her leg muscles.

A

44) 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.

A

48) Which of the following is FALSE regarding single-unit smooth muscle cells? A) They have an individual neuron innervating 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.

A

49) Which of the following properties of smooth muscle helps us to understand why, as pregnancy advances, women get more and more Braxton-Hicks (smooth muscle) contractions in the uterine wall? A) Smooth muscle cells contract in response to stretch. B) Smooth muscle cells contract in response to NO. C) Smooth muscle cells contract in response to CO2. D) Smooth muscle cells contract in response to changes in pH.

A

50) 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.

A

8) What would be the result if the administration of a drug sequesters all the ATP in a cell? A) All cross-bridges will remain tightly bound to actin. B) Calcium will remain in the cytosol, continuously stimulating cross-bridge cycling. C) Repeated, high-frequency action potentials will be fired at a skeletal muscle fiber causing sustained contraction. D) Calcium-activated proteases degrade all proteins in skeletal muscle fibers, making muscles limp. E) A build-up of K+ in T-tubules will cause constant, tetanic contractions of skeletal muscles.

A

110) (Select all that apply) A lack of ATP in the muscle cell will lead to A) calcium build-up in the cytosol. B) myosin heads becoming "stuck" in a bound configuration with actin. C) troponin unbinding from tropomyosin. D) frequent twitches with short periods of relaxation in between. E) sustained flaccid paralysis.

A, B

112) (Select all that apply) Why does breathing continue to be rapid and deep for a time after heavy exercise? A) Extra oxygen is needed to restore muscle creatine phosphate concentration. 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.

A, E

10) You have designed a drug that is supposed to bind to the myosin binding sites on actin. You inject it into a relaxed muscle, but find that none of the drug bound. Which of the following explains why? A) There are no myosin binding sites on actin. B) Troponin molecules are covering myosin binding sites on actin. C) The myosin binding sites are covered by ATP. D) The myosin binding sites on actin are covered by tropomyosin. E) None of the choices are correct.

D

13) With an implanted electrode you are able to cause an individual motor neuron that connects to the bicep muscle to fire an action potential. Which of the following is the most likely result? A) The entire bicep muscle contracts. B) A single muscle cell within the bicep muscle contracts. C) Between 10-1,000 muscle cells within the bicep muscle contract. D) It is impossible to predict based on this information alone.

D

17) As a muscle gets stronger the diameter of its individual muscle cells becomes larger. Which of the following structures ensures that the membrane potential change is translated into the depth of the cell? A) Z lines B) Sarcoplasmic reticulum C) H zone D) Transverse tubules E) Pores in the plasma membrane

D

20) The chemical curare is a nicotinic receptor antagonist. How will curare affect skeletal muscle function? A) It activates an autoimmune disease that destroys myelin. B) It will cause persistent twitches with short periods of rest in between. C) It will cause spastic paralysis (sustained, unwanted muscle contraction). D) It will cause flaccid paralysis (no muscle contraction possible). E) Muscle function is fine, but it will cause a loss of voluntary control.

D

25) 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.

D

37) 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.

D

42) If a biopsy of the quadriceps muscles (muscles on the front of the thigh) were taken from gold medal-winning speed skaters in the four following events, which would most likely have the SMALLEST percentage of type 1 muscle fibers? A) 10,000 meters B) 5,000 meters C) 1,000 meters D) 500 meters

D

46) 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, excitation-contraction coupling begins when an action potential propagates along the sarcoplasmic reticulum membrane.

D

47) 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.

D

9) 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.

D

18) If a muscle cell expressed muscarinic ACh channels, which are only permeable to Na+ instead of nicotinic ACh channels, which are permeable to both Na+ and K+, which portion of a muscle cell would be inhibited? A) Neurotransmitter release from the motor neuron B) Muscle cell depolarization C) Cross-bridge cycling D) Relaxation E) None of the answer choices are correct

E

27) 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.

E

36) 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

E

51) 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.

E

52) 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

E

56) 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 C) Sugar D) Protein E) Creatine

E