MED ANA 2B

C

1. Which characteristic best distinguishes skeletal muscle from cardiac and smooth muscle?
A. It contains actin and myosin
B. It is capable of producing an action potential
C. It is under voluntary control and normally requires innervation to contract
D. It contains calcium-sensitive regulatory proteins

B

2. A tissue contracts rhythmically even in the absence of external innervation and contains a pacemaker. Which muscle type is most consistent with this description?
A. Skeletal muscle
B. Cardiac muscle
C. Smooth muscle only
D. Skeletal and cardiac muscle equally

C

3. Which feature is shared by cardiac and smooth muscle according to the lecture?
A. Both are voluntary
B. Both lack pacemakers
C. Both are functionally syncytial
D. Both have prominent cross-striations

C

4. A histological specimen demonstrates prominent cross-striations and voluntary control. The tissue is most likely:
A. Smooth muscle
B. Cardiac muscle
C. Skeletal muscle
D. Visceral smooth muscle

D

5. Which contractile protein forms the thick filament?
A. Actin
B. Tropomyosin
C. Troponin
D. Myosin II

B

6. Which structure is primarily associated with the thin filament?
A. Myosin
B. Actin
C. Creatine kinase
D. ATP synthase

C

7. Which component of troponin contains the binding site for Ca²⁺?
A. Troponin I
B. Troponin T
C. Troponin C
D. Tropomyosin

C

8. What is the primary function of troponin I at rest?
A. It binds calcium
B. It binds ATP
C. It inhibits interaction between actin and myosin
D. It hydrolyzes ATP

B

9. Tropomyosin normally regulates contraction by:
A. Producing ATP for myosin
B. Covering myosin-binding sites on actin
C. Pumping Ca²⁺ into the sarcoplasmic reticulum
D. Binding directly to ATP

B

10. The globular head of myosin contains:
A. Only a calcium-binding site
B. An actin-binding site and ATP-hydrolyzing catalytic site
C. Only an ATP storage site
D. Troponin C and tropomyosin

B

11. The sarcotubular system consists primarily of the:
A. Sarcolemma and mitochondria
B. T system and sarcoplasmic reticulum
C. Myofibrils and Z lines
D. Actin and myosin

A

12. A triad is composed of:
A. One T tubule and two adjacent terminal cisternae
B. Two T tubules and one mitochondrion
C. One sarcoplasmic reticulum and two Z lines
D. Three myosin filaments

C

13. The major function of the T system is to:
A. Produce ATP
B. Store calcium permanently
C. Rapidly transmit action potentials from the cell membrane toward the fibrils
D. Bind calcium to troponin

D

14. The resting membrane potential of a skeletal muscle fiber is approximately:
A. −30 mV
B. −50 mV
C. −70 mV
D. −90 mV

A

15. The action potential duration in skeletal muscle is approximately:
A. 2–4 ms
B. 20–40 ms
C. 100 ms
D. 1 second

B

16. During depolarization of a skeletal muscle fiber, the principal ionic event is:
A. K⁺ influx
B. Na⁺ influx
C. Ca²⁺ efflux
D. Cl⁻ efflux

C

17. During repolarization of a skeletal muscle fiber, the principal ionic event is:
A. Na⁺ influx
B. Ca²⁺ influx
C. K⁺ efflux
D. Cl⁻ efflux

C

18. Which event occurs first when a motor neuron initiates skeletal muscle contraction?
A. Ca²⁺ binds to troponin C
B. Acetylcholine binds to nicotinic receptors
C. The motor neuron discharges and Ca²⁺ enters its nerve ending
D. Myosin binds actin

B

19. Calcium entering the motor nerve terminal directly triggers:
A. ATP production
B. Acetylcholine release
C. K⁺ influx into the muscle
D. Troponin activation

C

20. The neurotransmitter released at the skeletal neuromuscular junction is:
A. Dopamine
B. GABA
C. Acetylcholine
D. Glutamate

B

21. Acetylcholine produces its effect at the motor end plate primarily by binding to:
A. Muscarinic receptors
B. Nicotinic acetylcholine receptors
C. Voltage-gated calcium receptors
D. Troponin receptors

B

22. Nicotinic acetylcholine receptors at the neuromuscular junction are concentrated at the:
A. Z lines
B. Junctional folds
C. Terminal cisternae
D. Mitochondrial membrane

A

23. Activation of nicotinic acetylcholine receptors causes increased:
A. Na⁺ and K⁺ conductance
B. Ca²⁺ and Cl⁻ conductance only
C. ATP production
D. Calcium storage in the SR

B

24. The immediate electrical response produced at the motor end plate is called the:
A. Action potential
B. End-plate potential
C. Resting potential
D. Refractory potential

B

25. Which sequence correctly represents neuromuscular transmission?
A. ACh release → motor neuron discharge → Ca²⁺ binding troponin → action potential
B. Motor neuron discharge → Ca²⁺ enters nerve ending → ACh release → ACh binds receptor
C. Ca²⁺ binds troponin → ACh release → Na⁺ influx → motor neuron discharge
D. ACh binds troponin → Ca²⁺ release → action potential → myosin binding

B

26. After an action potential is generated in a skeletal muscle fiber, it spreads inward primarily through the:
A. Z lines
B. T tubules
C. Thin filaments
D. Myosin heads

B

27. Depolarization of the T tubules ultimately causes the sarcoplasmic reticulum to:
A. Take up Na⁺
B. Release Ca²⁺
C. Release ATP
D. Destroy acetylcholine

B

28. During excitation-contraction coupling, Ca²⁺ released from the sarcoplasmic reticulum diffuses toward the:
A. Nucleus only
B. Thick and thin filaments
C. Motor neuron
D. Mitochondria only

A

29. What is the critical event that allows actin-myosin interaction to begin?
A. Ca²⁺ binds troponin C
B. ATP is completely depleted
C. K⁺ enters the muscle fiber
D. Acetylcholine binds troponin

C

30. When Ca²⁺ binds to troponin C, the immediate consequence is:
A. Tropomyosin covers more actin-binding sites
B. Myosin is destroyed
C. Myosin-binding sites on actin become uncovered
D. Calcium is pumped back into the SR

B

31. At rest, tropomyosin prevents contraction primarily by:
A. Blocking myosin's ATP-binding site
B. Covering myosin-binding sites on actin
C. Preventing Ca²⁺ release from the nerve terminal
D. Blocking sodium channels

32. Which event directly follows exposure of myosin-binding sites on actin?
A. Formation of actin-myosin cross-linkages
B. Closure of all calcium channels
C. Breakdown of acetylcholine
D. Repolarization of the motor neuron

B

33. ATP hydrolysis during contraction produces:
A. AMP and glucose
B. ADP and Pi
C. Creatine and phosphate only
D. Ca²⁺ and Pi

B

34. The interaction between actin and myosin ultimately produces contraction through:
A. Separation of Z lines
B. Sliding of thin filaments on thick filaments
C. Shortening of the myosin molecules
D. Destruction of actin

B

35. Which structure remains approximately constant in width during skeletal muscle contraction?
A. I band
B. A band
C. Sarcoplasmic reticulum
D. Z line

36. During contraction, the Z lines:
A. Move farther apart
B. Disappear
C. Move closer together
D. Remain attached to the motor neuron

B

37. What must occur for a skeletal muscle fiber to relax?
A. More Ca²⁺ must be released from the SR
B. Ca²⁺ must be pumped back into the sarcoplasmic reticulum
C. ATP must be completely depleted
D. Sodium must remain inside the cell

B

38. During relaxation, Ca²⁺ is removed from the contractile apparatus primarily by:

A. Diffusion into the extracellular fluid

B. Active pumping back into the sarcoplasmic reticulum

C. Binding permanently to troponin C

D. Conversion into ATP

39. As Ca²⁺ dissociates from troponin during relaxation:
A. Actin-myosin interaction ceases
B. Myosin-binding sites remain exposed
C. More cross-bridges form
D. ATP production stops immediately

B

40. A drug prevents Ca²⁺ transport back into the sarcoplasmic reticulum. Which condition would most likely result?
A. Immediate flaccid paralysis
B. Contracture due to failure of relaxation
C. Complete inhibition of cross-bridge formation
D. Failure of acetylcholine release

D

41. Which is NOT listed as one of the three major mechanisms for ATP production in muscle fibers?
A. Creatine phosphate
B. Anaerobic cellular respiration
C. Aerobic cellular respiration
D. Protein translation

42. During short, intense activity, creatine phosphate is important because it:
A. Provides a rapid means of regenerating ATP
B. Requires large amounts of oxygen
C. Produces ATP only in mitochondria
D. Converts ATP directly into lactic acid

B

43. Creatine kinase catalyzes the reaction between:
A. ATP and oxygen
B. Creatine phosphate and ADP
C. Glucose and oxygen
D. Lactic acid and ATP

B

44. The creatine phosphate system is particularly important for approximately:
A. 1–2 seconds
B. 15 seconds
C. 5 minutes
D. Several hours

45. During anaerobic cellular respiration, glycolysis produces a net gain of approximately:
A. 1 ATP
B. 2 ATP
C. 10 ATP
D. 36 ATP

B

46. During oxygen-limited activity, pyruvic acid may be converted into:
A. Creatine phosphate
B. Lactic acid
C. Acetylcholine
D. Troponin

C

47. Which energy system is most important for prolonged activity such as a marathon?
A. Creatine phosphate system
B. Anaerobic glycolysis only
C. Aerobic cellular respiration
D. ATP stored in the muscle only

B

48. A patient develops muscle fatigue after prolonged activity. Which of the following is identified in the lecture as a possible contributor?
A. Excessive creatine phosphate availability
B. Depletion of glycogen
C. Excessive oxygen availability
D. Increased release of Ca²⁺ from the SR

B

49. Which type of contraction occurs without an appreciable decrease in the overall length of the muscle?
A. Isotonic
B. Isometric
C. Tetanic
D. Twitch

C

50. A long-distance runner requires muscle fibers with high oxidative capacity, abundant mitochondria and capillaries, and high fatigue resistance. Which fiber type is best suited for this activity?
A. Fast glycolytic fibers
B. Type II fast fibers
C. Slow oxidative fibers
D. Fast glycolytic white fibers