Skeletal Muscle Histology Quiz

Skeletal Muscle

• Skeletal muscles are consciously controlled and responsible for body movement; they are attached to bones.
• Muscle function includes posture maintenance, respiration and heat production.
• Skeletal muscles are made up of muscle fibers (cells) that are long, cylindrical and multinucleated.
• Myoblasts (immature muscle cells) fuse to form muscle fibers.
• Muscle fibers exhibit striations (light and dark bands due to protein organization).
• Skeletal muscles are composed primarily of muscle fibers (cells) surrounded by connective tissues, blood vessels, and nerves.

Muscle Histology

• Sarcolemma: The outer plasma membrane of a muscle cell.
• Sarcoplasm: The cytoplasm of a muscle cell, containing many mitochondria (powerhouses of the cell) for ATP production
• Myofibrils: Highly organized protein structures within muscle cells; they extend the entire length of the cell.
• Myofilaments: Contractile proteins (actin and myosin) form repeating patterns, creating sarcomeres, which are the basic contractile units.
• T-tubules: Invaginations of the sarcolemma, allowing action potentials to reach the interior of the muscle fiber, facilitating calcium release.
• Sarcoplasmic Reticulum (SR) Smooth ER that stores calcium ions and releases them during muscle contractions.
• Terminal cisternae: Enlarged regions of the SR adjacent to T-tubules, important for calcium storage.
• Triad: A unit formed by a T-tubule and two terminal cisternae.

Myofilaments

• Actin (thin filaments): made up of G-actin (globular proteins) with active sites for myosin binding; also includes tropomyosin and troponin.
• Myosin (thick filaments): made up of myosin filaments with heads that can bind to actin, driving contraction.
• Sarcomere: Structural and functional unit of muscle fibers, extending from Z-disc to Z-disc.
• Z-disc: Proteins that connect and organize actin filaments.
• M-line: Protein structure in the middle of the sarcomere, connecting myosin filaments.
• I-band: Region containing only actin filaments.
• H-zone: Region containing only myosin filaments.
• A-band: Region including both myosin and the overlapping portions of actin filaments.
• Cross-bridges: Myosin heads binding to actin during muscle contraction
• Myoglobin: Protein in muscle cells that binds and stores oxygen.
• Glycogen granules: Store carbohydrates for energy.

Gross Anatomy of Skeletal Muscle Structure

• Tendons: Dense connective tissue attaching muscle to bone.
• Fascicles: Bundles of muscle fibers.
• Endomysium: Connective tissue surrounding individual muscle fibers.
• Perimysium: Connective tissue surrounding fascicles.
• Epimysium: Connective tissue surrounding the entire muscle.
• Muscles are made up of multiple fascicles bundled together.

Muscle Fiber Structure and Properties

• Muscle cells are long, cylindrical, and multinucleated, containing myofibrils.
• Muscles can shorten by contracting and can elongate from other forces.
• They exhibit contractility (able to shorten), excitability (respond to APs), extensibility (extend beyond resting length), and elasticity (return to original length after extension).