Across
- 4. The myosin molecules’ globular heads that protrude from a thick filament within a muscle fiber and interact with the actin molecules in the thin filaments to bring about a shortening of the muscle fiber during contraction
- 5. A single muscle cell, which is relatively long and cylindrical in shape
- 6. Involuntary muscle in the walls of hollow organs and tubes innervated by the autonomic nervous system
- 9. One of the regulatory proteins in the thin filaments of muscle fibers
- 10. Specialized cytoskeletal structures within the skeletal muscle that are made up of actin, tropomyosin, and troponin molecules and interact with the thick filaments to shorten during muscle contraction
- 12. Striated muscle, which is attached to the skeleton and is responsible for the movement of the bones in purposeful relation to one another; innervated by the somatic nervous system and under voluntary control
- 13. One of the regulatory proteins in the thin filaments of muscle fibers
- 15. A giant, highly elastic protein that extends in both directions from the M line along the length of the thick filament to the Z lines and is responsible for the parallel elastic component of the muscle fiber
- 16. The functional unit of skeletal muscle; the area between two Z lines within a myofibril
- 22. A specialized intracellular structure of muscle cells that contains the contractile apparatus
- 23. A perpendicular in-folding of the surface membrane of a muscle fiber; rapidly spreads surface electric activity into the central portions of the muscle fiber
- 24. During embryonic development, the huge skeletal muscle fibers are formed by the fusion of many smaller cells
- 25. One of the light bands that alternate with dark (A) bands to create a striated appearance in a skeletal or cardiac muscle fiber when these fibers are viewed with a light microscope
Down
- 1. The ATP-powered cross-bridge binding and bending that pulls the thin filaments in closer together between the thick filaments during contraction of a muscle fiber
- 2. The smallest component of an organ that can perform all the functions of the organ
- 3. Troponin and tropomyosin, which play a role in regulating muscle contraction by either covering or exposing the sites of interaction between actin and the myosin cross-bridges
- 7. Spans the gap between the T tubule and the lateral sac and serve as Ca2+ release channels and are also known as ryanodine receptors
- 8. The specialized muscle found only in the heart
- 10. Specialized cytoskeletal structures within the skeletal muscle that are made up of myosin molecules and interact with the thin filaments to shorten the fiber during muscle contraction
- 11. One of the dark bands that alternate with light (I) bands to create a striated appearance in a skeletal or cardiac muscle fiber when these fibers are viewed with a light microscope
- 14. A fine meshwork of interconnected tubules that surrounds a muscle fiber’s myofibrils; contains expanded lateral sacs, which store calcium that is released into the cytosol in response to a local action potential
- 17. Supporting proteins that hold the thick filaments together vertically within each stack
- 18. The lighter area within the middle of the A band, where the thin filaments do not reach
- 19. The expanded saclike regions of a muscle fiber’s sarcoplasmic reticulum; store and release calcium, which plays a key role in triggering muscle contraction
- 20. The protein forming the thick filaments in muscle fibers
- 21. A flattened disclike cytoskeletal protein that connects the thin filaments of two adjoining sarcomeres