Unit 4: Mechanics of skeletal muscle - Practice Quiz

1 What is the basic structural and functional unit of a skeletal muscle?

2 The connective tissue sheath that surrounds an entire skeletal muscle is called the:

3 A bundle of muscle fibers grouped together is known as a:

4 The cell membrane of a muscle fiber is specifically called the:

5 The functional contractile unit of a myofibril, located between two Z-lines, is the:

6 Which two protein filaments are the main contractile proteins in a muscle fiber?

7 A motor unit consists of a single motor neuron and:

8 Muscles requiring fine, precise control (such as eye muscles) typically have motor units with:

9 The point where a motor neuron communicates with a muscle fiber is called the:

10 Which fiber type is best suited for prolonged, low-intensity endurance activity?

11 Fast-twitch (Type II) muscle fibers are characterized by:

12 Which fiber type generally contains a higher amount of myoglobin, giving it a red appearance?

13 In which muscle fiber arrangement do the fibers run parallel to the long axis of the muscle?

14 Pennate muscle architecture is associated with:

15 A muscle with fibers attaching to a central tendon on both sides is described as:

16 According to the sliding filament theory, muscle contraction occurs when:

17 During muscle contraction under the sliding filament theory, what happens to the distance between Z-lines?

18 Which ion must be released to trigger the interaction between actin and myosin during contraction?

19 Which molecule provides the energy required for the myosin cross-bridge cycle?

20 Hill's three-element muscle model includes a contractile element plus which two other elements?

21 A muscle biopsy shows connective tissue layers surrounding individual muscle fibers, bundles of fibers, and the entire muscle. Which layer directly surrounds a single muscle fiber?

22 The functional contractile unit of a skeletal muscle fiber, defined as the region between two adjacent Z-lines, is called the:

23 During contraction, which band of the sarcomere remains constant in width while others shorten?

24 The specialized smooth endoplasmic reticulum in a muscle fiber that stores and releases for contraction is the:

25 The thin filament of a muscle fiber is composed primarily of which protein?

26 A motor unit is best defined as:

27 Muscles requiring fine, precise control (e.g., extraocular eye muscles) typically have motor units with:

28 According to Henneman's size principle, motor units are recruited in what order as force demand increases?

29 Which fiber type is characterized by high oxidative capacity, high fatigue resistance, and slow contraction speed?

30 A sprinter's muscles are dominated by fibers that generate high force rapidly but fatigue quickly. These are most likely:

31 Which property is generally HIGHER in Type I fibers compared to Type II fibers?

32 In a pennate muscle, the muscle fibers are arranged at an angle to the tendon. This angle is known as the:

33 Compared to fusiform muscles of equal volume, pennate muscles typically produce:

34 The maximum force a muscle can produce is most directly proportional to its:

35 According to the sliding filament theory, muscle shortening occurs because:

36 During the cross-bridge cycle, the power stroke that pulls the thin filament is powered by:

37 At very long sarcomere lengths, active tension decreases because:

38 A muscle contracting while lengthening under load (e.g., lowering a heavy weight slowly) is performing what type of action?

39 In the force-velocity relationship of skeletal muscle, as the velocity of concentric shortening increases, the force the muscle can generate:

40 In Hill's three-element model of muscle, which component represents the active force generator?

41 A pennate muscle has a physiological cross-sectional area (PCSA) that is 3 times its anatomical cross-sectional area (ACSA), with a pennation angle of . Compared to a fusiform muscle of identical volume and fiber length, what is the approximate ratio of the pennate muscle's effective force transmitted along the tendon to the fusiform muscle's force?

42 According to the sliding filament theory, during isometric contraction at optimal sarcomere length, which structural observation would be experimentally expected?

43 In Hill's three-element model, a muscle is held at constant total length while the contractile element (CE) shortens. What must occur in the series elastic component (SEC) and why?

44 The Hill force-velocity equation is . If and the muscle contracts at , what fraction of maximum isometric force is produced?

45 According to the size principle (Henneman), during a graded increase in force, motor units are recruited in a specific order. Which combination correctly describes the earliest recruited units?

46 Two athletes are tested: sprinter X shows high glycolytic enzyme activity and low myoglobin; endurance runner Y shows high oxidative capacity and dense capillarization. Which fiber-type dominance and metabolic edge case best explains a Type IIx-to-IIa shift in Y after prolonged endurance training?

47 On the length-tension curve, a sarcomere at produces near-zero active tension. Given thick filament length and thin filament length each side, what is the biomechanical reason?

48 A quick-release experiment is performed on a maximally activated muscle. Immediately after release, tension drops instantaneously then redevelops. Which element accounts for the instantaneous drop?

49 In excitation-contraction coupling, a defect prevents the DHP receptor from mechanically coupling to the ryanodine receptor. What is the most direct functional consequence?

50 A muscle has fiber length , whole-muscle length , and shortens as a whole by . Assuming uniform fibers in series arrangement effects, what is the strain experienced by each fiber if the architectural gear ratio (AGR) equals 1?

51 During an eccentric contraction, muscle produces higher force than during isometric or concentric conditions at the same activation. Which combined mechanism best explains this enhanced force?

52 A motor unit is stimulated at increasing frequencies. At twitches partially summate (unfused tetanus); at force plateaus (fused tetanus). What determines the critical frequency for fusion?

53 Ranking connective tissue layers from innermost to outermost and their mechanical role, which sequence is correct?

54 In a Hill model where the parallel elastic component (PEC) is arranged parallel to the CE-SEC series unit, at a length below slack length what is the PEC's contribution to total tension?

55 A muscle produces force by both recruitment and rate coding. In small muscles (e.g., hand intrinsics), recruitment is complete at a relatively low percentage of maximum force. Beyond this, how is additional force primarily generated?

56 The descending limb of the length-tension curve is considered mechanically unstable in an isolated fiber. What is the biomechanical basis for this instability?

57 During the cross-bridge cycle, rigor mortis occurs because of a specific biochemical state. Which condition traps the myosin head?

58 Two muscles have equal volume and PCSA. Muscle A has short fibers with high pennation; Muscle B has long parallel fibers. Which statement about their functional specialization is correct?

59 A biarticular muscle can transfer power between joints without net length change—a phenomenon exploited in jumping. What property allows this energy transfer despite minimal contractile work?

60 During tetanic stimulation, calcium accumulates in the cytosol because reuptake by SERCA cannot keep pace. If SERCA activity is pharmacologically inhibited during a single twitch, what is the predicted effect on the twitch profile?