chapter 9 skeletal muscle organization

Introduction to Skeletal Muscle Organization

  • Focus on the macroscopic level of muscle organization down to muscle fibers.

  • Prepare for discussions on microanatomy in upcoming slides.

Understanding Muscle as Tissue and Organ

  • Skeletal muscle considered both a tissue and an organ.

  • Composed of multiple tissues; example: the bicep muscle.

Epimysium

  • Dense irregular connective tissue surrounding a muscle (e.g., bicep).

  • Distinguishes muscles from one another.

  • Blends into tendons or periosteum.

  • Related to deep fascia, a layer of connective tissue.

Fascicle Structure

  • Fascicles: Bundles of muscle fibers (myofibers).

  • Surrounded by perimysium, a layer of connective tissue.

  • Perimysium is also dense, irregular connective tissue, running lengthwise with muscles.

Muscle Fiber (Myofiber)

  • Myofiber: Multinucleated cell that is much larger than typical cells, hence called "fiber" instead of "cell."

  • Contains organelles: nuclei, mitochondria, ribosomes.

  • Surrounded by a unique plasma membrane called sarcolemma.

Connective Tissue Layers

  1. Epimysium: Outermost, surrounds the entire muscle.

  2. Perimysium: Middle layer, surrounds fascicles.

  3. Endomysium: Innermost layer, surrounds each muscle fiber and composed of loose areolar connective tissue.

Sarcolemma and Basement Membrane

  • Sarcolemma: Phospholipid bilayer with glycoproteins and cholesterol; defines internal environment of muscle fiber.

  • Basement membrane: Comprised of reticular fibers, located outside the sarcolemma.

Myofibril Structure

  • Myofibril: Unique to striated muscle, composed mainly of contractile proteins. -Made of sarcomeres, the smallest functional unit of muscle, arranged end to end.

Sarcomere Details

  • Sarcomere extends from one Z disc to another.

  • Contains thick filaments (myosin) and thin filaments (actin).

  • Thick filaments are centrally located; thin filaments connect to Z discs but do not overlap completely.

  • Interdigitation: Overlapping pattern of thick and thin filaments, contributing to muscle striations.

Striations and Banding Pattern

  • Organized protein structure results in visible striations in skeletal muscle.

  • Light bands (I bands): Isotropic regions where light can pass through.

  • Dark bands (A bands): Anisotropic regions that do not allow light through.

Conclusion

  • Overview of muscle structure prepares students for detailed discussions on protein organization in muscle.

  • Future slides will delve into individual proteins and their roles in muscle contraction.