Skeletal Muscle Components & Characteristics - Massage and Bodywork Licensing Examination Mblex

1. What is the I band in a sarcomere?

   Region containing thin filaments only. I bands represent areas without myosin overlap, shortening as filaments slide.

2. What neurotransmitter is released at the neuromuscular junction to stimulate skeletal muscle?

   Acetylcholine (ACh). It binds to nicotinic receptors on the sarcolemma, depolarizing the muscle fiber.

3. Which ion binds to troponin to move tropomyosin and allow cross-bridge formation?

   Calcium ($Ca^{2+}$). This ion's release from the SR triggers the exposure of actin's binding sites.

4. What is the basic functional unit of a skeletal muscle fiber that produces contraction?

   Sarcomere. It consists of organized myofilaments that enable the sliding filament mechanism for muscle shortening.

5. What is the H zone in a sarcomere?

   Central region with thick filaments only. The H zone lacks actin overlap, disappearing during full contraction.

6. Which myofilament is primarily composed of actin and is considered the thin filament?

   Thin filament (actin). Actin forms the structural backbone that interacts with myosin during contraction.

7. What is the connective tissue sheath that surrounds an individual muscle fiber (cell)?

   Endomysium. This delicate layer insulates individual fibers and facilitates nutrient exchange.

8. What is a triad in skeletal muscle histology?

   One T tubule plus two terminal cisternae of the SR. Triads facilitate rapid calcium release in response to action potentials for contraction.

9. During skeletal muscle contraction, which sarcomere region shortens: A band, I band, or H zone?

   I band and H zone shorten; A band remains constant. Sliding filaments cause overlap, reducing non-overlapping regions while thick filament length stays fixed.

10. What are myofibrils in a skeletal muscle fiber?

    Contractile organelles made of repeating sarcomeres. These structures run longitudinally and contain actin and myosin for force generation.

11. What is the sarcolemma in a skeletal muscle fiber?

    The muscle cell membrane. It encloses the muscle fiber and transmits action potentials to initiate contraction.

12. What is a transverse (T) tubule in skeletal muscle?

    A sarcolemma invagination that conducts the action potential. T tubules rapidly propagate electrical signals deep into the fiber to synchronize contraction.

13. What is the M line in a sarcomere?

    Midline where thick filaments are anchored. The M line stabilizes thick filaments at the sarcomere's center.

14. What is the motor unit in skeletal muscle physiology?

    One motor neuron and all muscle fibers it innervates. Motor units enable graded force through recruitment of varying fiber numbers.

15. What is the sarcoplasmic reticulum (SR) in skeletal muscle fibers?

    Specialized smooth ER that stores and releases calcium. The SR regulates calcium levels critical for excitation-contraction coupling.

16. What is a fascicle in skeletal muscle anatomy?

    A bundle of muscle fibers. Fascicles organize muscle fibers for coordinated contraction within the perimysium.

17. Which muscle fiber type is slow, oxidative, fatigue-resistant, and high in myoglobin?

    Type I (slow-twitch, oxidative) fibers. These fibers rely on aerobic metabolism for sustained, low-intensity activities like posture maintenance.

18. What is the connective tissue sheath that surrounds an entire skeletal muscle?

    Epimysium. This outermost layer provides structural support and separates the muscle from surrounding tissues.

19. Which myofilament is primarily composed of myosin and is considered the thick filament?

    Thick filament (myosin). Myosin's heads form cross-bridges with actin to produce sliding force.

20. What structure is the boundary between adjacent sarcomeres?

    Z disc (Z line). Z discs anchor thin filaments and define the sarcomere's repeating pattern.

21. What is the connective tissue sheath that surrounds a fascicle (bundle of fibers)?

    Perimysium. It groups muscle fibers into functional units and carries blood vessels and nerves.

22. What protein binds to actin and blocks myosin-binding sites at rest in skeletal muscle?

    Tropomyosin. It covers actin's active sites, preventing myosin attachment until calcium signals contraction.

23. What protein complex binds calcium to initiate skeletal muscle contraction?

    Troponin. Calcium binding causes a conformational change, exposing myosin-binding sites on actin.

24. What is the sarcoplasm in a skeletal muscle fiber?

    The muscle cell cytoplasm. It contains organelles, glycogen, and myoglobin essential for muscle metabolism.

25. What is the A band in a sarcomere?

    Region spanning the full length of thick filaments. The A band corresponds to myosin's length, remaining unchanged during contraction.

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