Muscle Histology MCQ. Contains 97 Most tested questions and Answers. Includes explanations.

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Muscle Histology 1. Skeletal and cardiac muscle, which are both striated, at resting length contain an A band in each sarcomere. This A band contains: (A) Essentially all the contractile protein my... osin, but no actin (B) Essentially all the contractile protein actin, but no myosin (C) Essentially all the myosin, plus some actin (D) Essentially all the actin, plus some myosin (E) Troponin and tropomyosin, but no actin 2. When skeletal muscle shortens in response to stimulation, there is... (A) A decrease in the width of the I band (B) A decrease in the width of the A band (C) An increase in the width of the H zone (D) All of the above (E) A and B (F) None of the above 3. Which of the following decreases in length during the contraction of a skeletal muscle fiber? (A) A band of the sarcomere (B) I band of the sarcomere (C) Thick filaments (D) Thin filaments (E) Z discs of the sarcomere 4. A person lifting up their physiology textbook contracts their bicep muscle isotonically. Which one of the following does not change its length in this process when compared to when the muscle is at rest? (A) I band (B) A band (C) H zone (D) Sarcomere (E) Biceps tendon 5. A cross-sectional view of a skeletal muscle fiber through the H zone would reveal the presence of what? (A) Actin and titin (B) Actin, but no myosin (C) Actin, myosin, and titin (D) Myosin and actin (E) Myosin, but no actin 6. Which of the following binds Ca2+ in order to uncover the active site on F-actin? (A) Actin monomer (B) Myosin (C) Tropomyosin (D) Troponin (E) Crossbridge 7. A 64-year-old man was admitted to the hospital with edema and congestive heart failure. He was found to have diastolic dysfunction characterized by inadequate filling of the heart during diastole. The decrease in ventricular filling is due to a decrease in ventricular muscle compliance. Which of the following proteins determines the normal stiffness of ventricular muscle? (A) Calmodulin (B) Troponin (C) Tropomyosin (D) Titin (E) Myosin light chain kinase 8. In skeletal muscle, which of the following events occurs before depolarization of the T tubules in the mechanism of excitation-contraction coupling? (A) Depolarization of the sarcrolemmal membrane (B) Opening of Ca2+ release channels on the sarcoplasmic reticulum (C) Uptake of Ca2+ into the sarcoplasmic reticulum by Ca2+-ATPase (D) Binding of Ca2+ to troponin C (E) Binding of actin and myosin 9. Which of the following best describes the action potential of skeletal muscle upon stimulation? (A) It spreads inward to all parts of the muscle via the T-tubules (B) It has a prolonged plateau phase (C) It causes the immediate uptake of Ca2+ into the lateral sacs of SR (D) It is longer than the action potential of cardiac muscle (E) It is not essential for contraction 10. The action potential of skeletal muscle: (A) Has a prolonged plateau phase (B) Spreads inward to all parts of the muscle via T-tubules (C) Causes the immediate uptake of calcium into the lateral sacs of sarcoplasmic reticulum (D) Is longer than the action potential of cardiac muscle (E) Is not essential for muscle contraction in the intact muscle 11. Depolarization of the T tubule is directly linked to the opening of Ca2+ channels on the sarcoplasmic reticulum (SR) of… (A) Skeletal muscle (B) Cardiac muscle (C) Both A and B (D) None of the above 12. In a normal, healthy muscle, what occurs as a result of propagation of an action potential to the terminal membrane of a motor neuron? (A) Opening of voltage-gated Ca2+ channels in the presynaptic membrane (B) Depolarization of the T tubule membrane follows (C) Always results in muscle contraction (D) Increase in intracellular Ca2+ concentration in the motor neuron terminal (E) All of the above are correct 13. At the muscle end-plate, acetylcholine (ACh) caused the opening of… (A) Na+ channels and depolarization toward the ENa (B) K+ channels and depolarization toward the EK (C) Ca2+ channels and depolarization toward the ECa (D) Na+ and K+ channels and depolarization to a value halfway between the ENa and EK (E) Na+ and K+ channels and hyperpolarization to a value halfway between the ENa and EK 14. Which of the following is true about the synaptic channels on the endplate of skeletal muscle? (A) They are highly selective for Na+ (B) They are opened when the cell membrane depolarizes (C) They are activated by acetylcholine (ACh) (D) They are inhibited by atropine (E) They are responsible for the relative refractory period (A) Will initiate a contraction in response to the local application of acetylcholine (B) Will depolarize when exposed to an excess of extracellular K+ (C) Will depolarize in response to an excess of extracellular Ca2+ (D) Has all of the above characteristics (E) Has none of the above characteristics 16. The end-plate potential of skeletal muscle is best characterized as: (A) A local reversal of charge originating at the end-plate (B) A reversal of charge originating at the end-plate and propagated throughout the cell (C) A decrease in the transmembrane potential that is propagated throughout the cell (D) A local decrease in the transmembrane potential that is caused by an increased permeability to Na+ and K+ (E) A local decrease in the transmembrane potential that is associated with little or no increase in Na+ conductance 17. Which one of the following is directly associated with the motor endplate potential? (A) Ca2+ entry through voltage-dependent channels on the axon terminal (B) Acetylcholine release from the nerve terminal (C) Na+ entry through nicotinic channels on the muscle membrane (D) Na+ entry through voltage-dependent channels on the muscle membrane (E) Ca2+ entry through dihydropyridine channels in the transverse tubule 18. Mary has just found out that she is suffering from myasthenia gravis, an autoimmune disease that decreases the number of nicotinic receptors on the muscle membrane of the neuromuscular junction. She has been told to take a cholinesterase inhibitor which increases the concentration of acetylcholine at the neuromuscular junction. The binding of acetylcholine to the nicotinic receptors at the neuromuscular junction stimulate the influx of what ion into the muscle cell? (A) Potassium (B) Sodium (C) Calcium (D) Chlorine (E) Nicotine 19. A 30-year-old woman is running the Boston marathon. In regard to the physiology of her different muscle tissue types, an increase in sodium conductance is associated with which of the following? (A) The plateau phase of the ventricular muscle action potential in heart (B) The downstroke of the skeletal muscle action potential (C) The upstroke of the smooth muscle action potential (D) The refractory period of the nerve cell action potential (E) The end-plate potential of the skeletal muscle fiber 20. Which of the following temporal sequences is correct for excitation-contraction coupling in skeletal muscle? (A) Increased intracellular [Ca2+]; action potential in the muscle membrane; cross-bridge formation (B) Action potential in the muscle membrane; depolarization of the T tubules; release of Ca2+ from the sarcoplasmic reticulum (SR) (C) Action potential in the muscle membrane; splitting of adenosine triphosphate (ATP); binding of Ca2+ to troponin C (D) Release of Ca2+ from the sarcoplasmic reticulum (SR); depolarization of the T tubules; binding of Ca2+ to troponin C 21. Which of the following statements about smooth muscle contraction is most accurate? (A) Ca2+ independent (B) Does not require an action potential (C) Requires more energy compared to skeletal muscle (D) Shorter in duration compared to skeletal muscle 22. Which of the following best defines contraction? (A) A series of chemical reactions that cause the muscle to pull (B) A series of chemical reactions that cause the muscle to shorten (C) A series of chemical reaction in which the muscle respond to stimulate (D) Shortening (E) Production of tension 23. Skeletal muscle contraction... (A) Equals the duration of the action potential (B) Equals the duration of the absolute refractory period (C) Precedes the refractory period (D) Ends immediately after the refractory period is over (E) All of the above (F) A and C (G) None of the above 24. Check each of the following statements about skeletal muscle contraction that is true. (A) The major function of the T system (transverse tubules) is to store and release Ca2+. (B) The intracellular release of Ca2+ causes the formation of bonds between actin and myosin. (C) The bonds between actin and myosin are maintained until the Ca2+ is sequestered. (D) All of the above (E) B and C (F) None of the above 25. Which of the following best describes the contractile response of skeletal muscle? (A) It starts after the action potential (B) It does not last as long as the action potential (C) It produces more tension when the muscle contract isometrically than isotonically (D) It produces more tension when the muscle contract isotonically than isometrically (E) It decreases in magnitude with repeated stimulation 26. During an isometric contraction in vivo... (A) The total tension in the muscle is generated from actin-myosin cross-bridge (B) Intracellular free Ca2+ is lower than under resting conditions (C) ATPase activity of the sarcoplasmic reticulum is inhibited (D) Troponin-bound Ca2+ is required to maintain active tension (E) The Na+/K+-ATPase pump is actively inhibited 27. In a series of experiments, it is noted that in a skeletal muscle fiber an intracellular concentration of Ca2+ of 10–6.5 mol/L is the threshold value needed for inducing contraction. On this basis, one would expect a concentration of 10–5.5 mol/L of Ca2+ to cause: (A) A more forceful contraction (B) A less forceful contraction (C) A contraction of equal force (D) Relaxation 28. A newly discovered toxin incapacitated skeletal muscle by preventing the binding of ATP to the myosin cross-bridges. Which of the following would be expected in the affected muscle? (A) Decreased resting muscle compliance (B) A reduced sequestration of Ca2+ by the sarcoplasmic reticulum (C) Reduced Ca2+ release by the sarcoplasmic reticulum (D) Enhanced binding of ADP to myosin (E) A 50% reduction in the ability to develop active tension 29. Which one of the following groups matches the following statement? This group of muscles requires calcium to bind to troponin C to initiate the contractile state. (A) Skeletal muscle only (B) Skeletal and cardiac muscle only (C) Cardiac muscle only (D) Cardiac and smooth muscle only (E) Smooth muscle only 30. Which one of the following proteins is important for skeletal muscle contraction but not for smooth muscle contraction? (A) Actin (B) Myosin (C) Troponin (D) Myosin-adenosine triphophatase (ATPase) (E) Ca2+-ATPase 31. You are comparing the structure of skeletal and smooth muscle. Which one of the following is only associated with skeletal muscle? (A) Myosin (B) Actin (C) Myosin light chains (D) Troponin (E) Tropomyosin 32. In order to initiate the processes involved in smooth muscle contraction calcium must bind to which one of the following proteins? (A) Troponin C (B) Myosin light chain kinase (C) Calsequestrin (D) Calmodulin (E) Ryanodine receptor 33. Calmodulin is most closely related, both structurally and functionally, to which of the following proteins? (A) G-actin (B) Myosin light chain (C) Tropomyosin (D) Troponin C 34. Excitation-contraction coupling in skeletal muscle involves all of the following events EXCEPT one. Which one is this EXCEPTION? (A) ATP hydrolysis (B) Binding of Ca2+ to calmodulin (C) Conformational change in dihydropyridine receptor (D) Depolarization of the transverse tubule (T tubule) membrane (E) Increased Na+ conductance of sarcolemma 35. The functions of tropomyosin in skeletal muscle include: (A) Sliding on actin to produce shortening (B) Releasing calcium after initiation of contraction (C) Binding of myosin during contraction (D) Covering up the sites where myosin binds to actin in resting muscle (E) Generating ATP, which it passes to the contractile mechanism 36. Malignant hyperthermia is a potentially fatal genetic disorder characterized by a hyperresponsiveness to inhaled anesthetics and results in elevated body temperature, skeletal muscle rigidity, and lactic acidosis. Which of the following molecular changes could account for these clinical manifestations? (A) Decreased voltage sensitivity of the dihydropyridine receptor (B) Enhanced activity of the sarcoplasmic reticulum Ca2+ -ATPase (C) Prolonged opening of the ryanodine receptor channel (D) Reduction in the density of voltage-sensitive Na+ channels in the T tubule membrane 37. A 32-year-old woman undergoing surgery developed malignant hyperthermia following halothane anesthesia. The life-threatening increase in metabolic rate and body temperature is attributed to a mutation of the ryanodine receptor in skeletal muscle, resulting in which of the following? (A) Excess Ca2+ release from the SR during muscle contraction (B) Rapid repetitive firing of presynaptic terminals of motorneurons (C) Inability of skeletal muscle cells to repolarize (D) An increase in the refractory period of the motoneurons (E) Production of endogenous muscle pyrogens 38. The rate at which Ca2+ is sequestered by the sarcoplasmic reticulum of skeletal muscle during a twitch is directly related to: (A) The rate of tension development (B) The rate of ATP hydrolysis by myosin (C) The rate of relaxation (D) The height of the action potential (E) All of the above (F) None of the above 39. A single contraction of skeletal muscle is most likely to be terminated by which of the following actions? (A) Closure of the postsynaptic nicotinic acetylcholine receptor (B) Removal of acetylcholine from the neuromuscular junction (C) Removal of Ca2+ from the terminal of the motor neuron (D) Removal of sarcoplasmic Ca2+ (E) Return of the dihydropyridine receptor to its resting conformation 40. Smooth muscle contraction is terminated by which of the following? (A) Dephosphorylation of myosin kinase (B) Dephosphorylation of myosin light chain (C) Efflux of Ca2+ ions across the plasma membrane (D) Inhibition of myosin phosphatase (E) Uptake of Ca2+ ions into the sarcoplasmic reticulum 41. You are charged with the responsibility of developing a new drug to treat muscle spasticity following spinal cord injury. Which of the following characteristics would be most useful in treating this condition? (A) Inhibition of protein kinases (B) Inhibition of the Ca2+-dependent ATPase of the sarcoplasmic reticulum (C) Blocking the opening of Ca2+ channels in the cell membrane (D) Inhibition of Ca2+ release from the sarcoplasmic reticulum (E) Activation of voltage-gated Ca2+ channels of the T-tubular membrane system 42. When comparing the contractile responses in smooth and skeletal muscle, which of the following is most different? (A) The source of activator Ca2+ (B) The role of Ca2+ in initiating contraction (C) The mechanism of force generation (D) The source of energy used during contraction (E) The nature of the contractile proteins 43. Which of the following best represents the muscle type(s) that require Ca2+-induced Ca2+ release in order to initiate contraction? (A) Cardiac muscle (B) Skeletal muscle (C) Smooth muscle (D) Cardiac and skeletal muscle (E) Cardiac and smooth muscle 44. Similarities between smooth and cardiac muscle include which of the following? (A) Ability to contract in the absence of an ac-tion potential (B) Dependence of contraction on Ca2+ ions (C) Presence of a T tubule network (D) Role of myosin kinase in muscle contrac-tion (E) Striated arrangement of the actin and my-osin filaments 45. The delayed onset and prolonged duration of smooth muscle contraction, as well as the greater force generated by smooth muscle compared with skeletal muscle, are all consequences of which of the following? (A) Greater amount of myosin filaments present in smooth muscle (B) Higher energy requirement of smooth muscle (C) Physical arrangement of actin and myosin filaments (D) Slower cycling rate of the smooth muscle myosin cross-bridges (E) Slower uptake of Ca2+ ions following contraction 46. Which of the following best describes an attribute of visceral smooth muscle not shared by skeletal muscle? (A) Contraction is ATP dependent (B) Contracts in response to stretch (C) Does not contain actin filaments (D) High rate of cross-bridge cycling (E) Low maximal force of contraction 47. Smooth muscle that exhibits rhythmical contraction in the absence of external stimuli also necessarily exhibits which of the following? (A) “Slow” voltage-sensitive Ca2+ channels (B) Intrinsic pacemaker wave activity (C) Higher resting cytosolic Ca2+ concentration (D) Hyperpolarized membrane potential (E) Action potentials with “plateaus” 48. The sensitivity of the smooth muscle contractile apparatus to calcium is known to increase in the steady-state under normal conditions. This increase in calcium sensitivity can be attributed to a decrease in the levels of which of the following substances? (A) Actin (B) Adenosine Triphosphate (ATP) (C) Calcium-calmodulin complex (D) Calmodulin (E) Myosin light chain phosphatase (MLCP) 49. A 32-year-old man is diagnosed with primary hypertension. His physician recommends a drug for hypertension that acts by decreasing vascular smooth muscle contractile activity without affecting ventricular contractility. Which of the following is the most likely site of action for the drug? (A) β-Adrenergic receptors (B) Calmodulin (C) Troponin (D) Tropomyosin (E) Protein kinase A 50. An experimental drug is being tested as a potential therapeutic treatment for asthma. Preclinical studies have shown that this drug induces the relaxation of cultured porcine tracheal smooth muscle cells pre-contracted with acetylcholine. Which of the following mechanisms of action is most likely to induce this effect? (A) Decreased affinity of troponin C for Ca2+ (B) Decreased plasma membrane K+ permeability (C) Increased plasma membrane Na+ permeability (D) Inhibition of the sarcoplasmic reticulum Ca2+-ATPase (E) Stimulation of adenylate cyclase 51. In smooth muscle, Ca2+ is release from the sarcoplasmic reticulum (SR) by which of the following? (A) Diacylglycerol (DAG) (B) The guanosine triphosphate (GTP) binding protein (G protein) (C) Phospholipase C (PLC) (D) Inositol triphosphate (IP3) (E) Adenylate cyclase 52. Increasing the afterload on skeletal muscle fiber… (A) Increases the velocity of shortening (B) Decreases the force produced by the muscle during shortening (C) Decreases the interval between excitation and shortening (D) Increases the amount of shortening (E) None of the above 53. All of the following will occur when an unstimulated muscle is stretched except... (A) Increased preload (B) Increased afterload (C) Increased muscle length (D) Increased passive tension 54. Which of the following statements is true? (A) A muscle at resting length exerts its maximum force during an isotonic contraction (B) The maximum velocity of shortening during contraction occurs when there is no afterload (C) The preload is the weight the muscle moves before it starts to relax (D) In most form of muscle contraction in an intact individual, the preload and afterload are equal (E) All of the above (F) A and B (G) C and D (H) B and D (I) None of the above 55. Alteration in preload alters the force of contractions in which of the following muscle type of types? (A) Cardiac muscle (B) Skeletal muscle (C) Smooth and cardiac muscle (D) Smooth and skeletal muscle (E) Smooth, cardiac, and skeletal muscle 56. The diagram shows the force-velocity relationship for isotonic contractions of skeletal muscle. The differences in the three curves result from differences in which of the following? (A) Frequency of muscle contraction (B) Hypertrophy (C) Muscle mass (D) Myosin ATPase activity (E) Recruitment of motor units 57. Illustrates differences in the force-velocity relationship of skeletal muscle caused by changes in myosin ATPase activity. (A) Figure A (B) Figure B (C) Neither figure 58. In the diagram below, the shift from curve X to curve Y could be produced by: (A) Changes in afterload (B) Changes in preload (C) Changes in myosin ATPase activity (D) Changes in number of active cross-bridges (E) Spatial summation of fibers 59. The following diagram shows the chart records taken from an isolated skeletal muscle contracting against various loads. Both the length and force produced by the muscle were measured, the X-axis represents time. An upward deflection indicates shortening on the length trace. The muscle resting length was kept constant throughout the data recording. In which diagram does the muscle produce the fastest shortening velocity? 60. The following diagram shows the force velocity relationship obtained from a single skeletal muscle fibre. All data is taken on the ascending limb of the length tension curve. The numbers identify the curve to their right. Which one of the following curves is produced when the muscle is at the shortest length? 61. Use the force-velocity diagrams, from the same muscle, below to answer the following question. Which one of the following statements must be true when comparing Point 1 to Point 2? (A) Point 1 is at a shorter resting muscle length (B) Point 1 is on a curve that has a greater maximum velocity of shortening (C) Point 1 is lifting a greater load (D) Point 1 utilizes less energy (E) At Point 1 no shortening occurs 62. Using the two force-velocity curves, taken at muscle lengths on the ascending limb of the lengthtension relationship, shown in the graph below which one of the following statements is true under all circumstances? (A) The two curves are from two different muscles (B) The curve on which you find Point B is of a muscle that will always produce more isometric force than that indicated by the curve with Point A (C) The shortening is quicker at Point B than at Point A (D) The afterload at point A is less than at point B (E) Curve B is taken from a fast-twitch muscle 63. Illustrates differences in the force-velocity relationship of skeletal muscle caused by changes in recruitment of additional motor units. (A) Figure A (B) Figure B (C) Neither figure 64. Use the following diagram of the active length tension curve from an in vitro skeletal muscle preparation to answer the question. Which circle is at a sarcomere length where there is the most crossbridge attachment occurring during contraction? 65. During the resting state, a single skeletal muscle sarcomere can exist at a number of lengths. During an isometric contraction, the length at which it can exert its maximum force in response to stimulation is: (A) 1.7 μm (B) 2.2 μm (C) 3.0 μm (D) All of the above (E) Both B and C 66. The figure below depicts the isometric length-tension relationship of skeletal muscle. Identify the region where actin and myosin overlap is the least. 67. The diagram shows the length-tension relationship for a single sarcomere. Why is the tension development maximal between points B and C? (A) Actin filaments are overlapping each other (B) Myosin filaments are overlapping each other (C) The myosin filament is at its minimal length (D) The Z discs of the sarcomere abut the ends of the myosin filament (E) There is optimal overlap between the actin and myosin filaments (F) There is minimal overlap between the actin and myosin filaments 68. Use the figure below for this question: A change in resting skeletal muscle length from “c” to “e” results in: (A) A decrease in actin and myosin interaction (B) Reduced Ca2+ sensitivity of tropomyosin (C) Bending and folding of the thick filaments (D) Increased release of Ca2+ from terminal cisternae (E) Reduced entry of Ca2+ into the fiber during the action potential 69. So-called “active” or contraction-dependent tension. 70. The muscle length at which active tension is maximal. 71. The contribution of non-contractile muscle elements to total tension. 72. Which point represents a preload of 40 g? (A) Point 3 (B) Point 4 (C) Point 8 (D) Points 4 and 8 (E) Points 3, 4, and 8 73. Maximal active tension in the diagram is developed by skeletal muscle at point(s): (A) Point 1 (B) Point 2 (C) Point 4 (D) Points 3 and 4 (E) Point 9 74. Which point(s) in the diagram represent(s) no overlap between most of the muscle’s thick and thin filaments? Point(s): (A) Point 2 (B) Point 3 (C) Point 6 (D) Point 7 (E) Points 6 and 7 75. If a muscle was at point 4 on the passive curve, what is the active tension generated during stimulation? (A) Less than 40 g (B) 40 to 60 g (C) 60 to 80 g (D) 80 to 100 g 76. The length-tension diagram shown here was obtained from a skeletal muscle with equal numbers of red and white fibers. Supramaximal tetanic stimuli were used to initiate an isometric contraction at each muscle length studied. The resting length was 20 cm. What is the maximum amount of active tension that the muscle is capable of generating at a preload of 100 grams? (A) 145-155 grams (B) 25-35 grams (C) 55-65 grams (D) 95-105 grams (E) Cannot be determined 77. Use the following diagram of the length tension curve from an in vitro skeletal muscle preparation to answer the question. The dark blue line represents active tension, the green line passive tension. Which circle is at a sarcomere length where there is the greatest total tension produced during a contraction? 78. A severe laceration to a write completely severed a major muscle tendon. To reattach the tendon, the severed ends were overlapped by 7.5 cm before suturing. After recovery, which of the following could be expected compared with the preinjured muscle? (A) Increased passive tension and decreased maximal active tension (B) Decreased passive tension and decreased maximal active tension (C) Increased passive tension and increased maximal active tension (D) Increased passive tension and same maximal active tension (E) Same passive tension and same maximal active tension 79. A 24-year-old woman is admitted as an emergency to University Hospital following an automobile accident in which severe lacerations to the left wrist severed a major muscle tendon. The severed ends of the tendon were overlapped by 6 cm to facilitate suturing and reattachment. Which of the following would be expected after 6 weeks compared to the preinjured muscle? Assume that series growth of sarcomeres cannot be completed within 6 weeks. Passive tension Maximal active tension (A) Decrease Decrease (B) Decrease Increase (C) Increase Increase (D) Increase Decrease (E) No change No change 80. The following diagram shows the chart records taken from an isolated skeletal muscle contracting against various loads. Both the length and force produced by the muscle were measured, the X-axis represents time. An upward deflection indicates shortening on the length trace. The muscle resting length was kept constant throughout the data recording. Which one of the chart recordings show the muscle undergoing isometric contractions? 81. If the gastrocnemius muscle is removed from the body, it will achieve a length... (A) Greater than it had in the body, because it is more relaxed (B) Shorter than it had in the body, because it is less relaxed (C) Shorter than it had in the body, because it its elastic characteristics (D) The same as it had in the body 82. In an isometric contraction of a skeletal muscle, force of contraction cannot be altered by... (A) Changing the resting length of the muscle (B) Increasing stimulation frequency (C) Increasing the number of sarcomeres in parallel in the muscle (D) Increasing the number of sarcomeres in series in the muscle 83. Weightlifting can result in a dramatic increase in skeletal muscle mass, This increase in muscle mass is primarily attributable to which of the following? (A) Fusion of sarcomeres between adjacent myofibrils (B) Hypertrophy of individual muscle fibers (C) Increase in skeletal muscle blood supply (D) Increase in the number of motor neurons (E) Increase in the number of neuromuscular junctions 84. A 17-year-old soccer player suffered a fracture to the left tibia. After her lower leg has been in a cast for 8 weeks, she is surprised to find that the left gastrocnemius muscle is significantly smaller in circumference than it was before the fracture. What is the most likely explanation? (A) Decrease in the number of individual muscle fibers in the left gastrocnemius (B) Decrease in blood flow to the muscle caused by constriction from the cast (C) Temporary reduction in actin and myosin protein synthesis (D) Increase in glycolytic activity in the affected muscle (E) Progressive denervation 85. Which of the following characteristics of skeletal muscle make tetanic contraction possible? (A) The motor neurons to skeletal muscle have a short refractory period and are therefore capable of delivering a high frequency of stimuli to a muscle fiber (B) The cell membrane of the skeletal muscle fiber recovers its excitability well before the cell ceases its contraction (C) The prolonged exposure of the muscle end plate to high concentrations of acetylcholine throughout the tetanus (D) The action potential of skeletal muse outlasts the period of contraction (E) All of the above (F) A and B (G) A, B and C (H) None of the above 86. The amount of force produced by a skeletal muscle can be increased by which of the following? (A) Increasing extracellular Ca2+ (B) Decreasing extracellular Ca2+ (C) Increasing the activity of AChE (D) Decreasing the interval between contractions (E) Increasing the preload (in vivo) 87. The force produced by a single skeletal muscle fiber can be increased by which of the following? (A) Decreasing extracellular K+ concentration (B) Increasing the amplitude of the depolarizing stimulus (C) Increasing the frequency of stimulation of the fiber (D) Increasing the number of voltage-gated Na+ channels in the sarcolemma (E) Increasing the permeability of the sarcolemma to K+ 88. Repetitive stimulation of a skeletal muscle fiber will cause an increase in contractile strength due to an increase in which of the following? (A) The duration of cross-bridge cycling (B) The concentration of Ca2+ in the myoplasm during contraction (C) The magnitude of the end-plate potential (D) The number of muscle myofibrils generating tension (E) The velocity of muscle contraction 89. Which of the following best describes the reason why you can tetanize skeletal but not cardiac muscle? (A) The myosin ATPase activity is greater in skeletal muscle when compared to cardiac muscle (B) Ca2+-induced Ca2+-release does not allow for tetanization to take place in cardiac muscle (C) The length tension relationship for cardiac muscle is shorter than that of skeletal muscle (D) The duration of muscle contraction is longer in skeletal muscle (E) The ratio of action potential duration to twitch duration is much less in skeletal muscle 90. Tetanic contraction of a skeletal muscle fiber results from a cumulative increase in the intracellular concentration of which of the following? (A) ATP (B) Ca2+ (C) K+ (D) Na+ (E) Troponin 91. Post-tetanic facilitation is thought to be the result of… (A) Opening voltage-gated sodium channels (B) Opening transmitter gated potassium chan-nels (C) A buildup of calcium in the presynaptic terminal (D) Electrotonic conduction 92. During a demonstration for medical students, a neurologist uses magnetic cortical stimulation to trigger firing of the ulnar nerve in a volunteer. At relatively low-amplitude stimulation, action potentials are recorded only from muscle fibers in the index finger. As the amplitude of the stimulation is increased, action potentials are recorded from muscle fibers in both the index finger and the biceps muscle. What is the fundamental principle underlying this amplitude-dependent response? (A) Large motor neurons that innervate large motor units require a larger depolarizing stimulus (B) Recruitment of multiple motor units requires a larger depolarizing stimulus (C) The biceps muscle is innervated by more motor neurons (D) The motor units in the biceps are smaller than those in the muscles of the fingers (E) The muscles in the fingers are innervated only by the ulnar nerve 93. Which of the following best describes muscle B, when compared to muscle A? (A) Adapted for rapid contraction (B) Composed of larger muscle fibers (C) Fewer mitochondria (D) Innervated by smaller nerve fibers (E) Less extensive blood supply 94. The delay between the termination of the transient depolarization of the muscle membrane and the onset of muscle contraction observed in both muscles A and B reflects the time necessary for which of the following events to occur? (A) ADP to be released from the myosin head (B) ATP to be synthesized (C) Ca2+ to accumulate in the sarcoplasm (D) G-actin to polymerize into F-actin (E) Myosin head to complete one cross-bridge cycle 95. The slow twitch muscle fiber differs from the fast twitch fiber because the slow twitch fiber... (A) Has a smaller number of muscle fibers in each motor unit but equally powerful (B) Has a higher concentration of myoglobin and mitochondria (C) Has a higher ATPase activity (D) In a large limb serves as a reserve which can be recruited if there is a forceful contraction (E) Is more readily fatigued (F) Is part of a motor unit that consists mainly of red fibers 96. A 16-year-old adolescent boy on the track team asks his pediatrician if he can take creatine on a regular basis in order to increase his muscle strength prior to a track meet. Which of the following most likely explains why he wants to take creatine? (A) Creatine increases plasma glucose concentrations (B) Creatine prevents dehydration (C) Creatine increases muscleglycogen concentrations (D) Creatine is converted to phosphocreatine (E) Creatine delays the metabolism of fatty acids 97. During the initial stages of a muscle contraction (first few seconds) ATP stores are mainly replenished by: (A) The breakdown of muscle glycogen stores (B) Anaerobic glycolysis (C) Rephosphorylation by creatine phosphate (D) Oxidative phosphorylation of pyruvate (E) Oxidative phosphorylation of fatty acids [Show More]

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