Muscle Structure Flashcards

Connective Tissue Structures

• Epimysium: Dense connective tissue layer surrounding an entire muscle, providing structural support and protection.
• Perimysium: Connective tissue that groups muscle fibers into bundles called fascicles, containing blood vessels and nerves.
• Endomysium: Thin connective tissue layer encasing individual muscle fibers, allowing for interaction between muscle cells and nerves.

Muscle Structures

• Tendon: Connective tissue that attaches muscle to bone, transmitting the force generated by muscles during contraction.
• Aponeurosis: Flat sheet of connective tissue that connects muscles to muscles or to other structures, serving a similar role as tendons.
• Muscle Fiber: Basic unit of muscle tissue, long multinucleated cells capable of contraction and force generation.

Cellular Components

• Sarcolemma: Plasma membrane surrounding each muscle fiber, playing a crucial role in muscle contraction by conducting electrical impulses.
• Myofibrils: Rod-like structures within muscle fibers, composed of repeating units called sarcomeres, responsible for muscle contraction.
• Myofilaments: The contractile proteins within myofibrils, divided into thick (myosin) and thin (actin) filaments.

Filament Proteins

• Thin Filaments: Composed primarily of actin, along with regulatory proteins such as tropomyosin and troponin, essential for muscle contraction regulation.

  • Actin: Globular protein that polymerizes to form thin filaments.
  • G Actin: Monomeric form of actin, the building block of filamentous actin.
  • F Actin: Filamentous form of actin, formed from G actin subunits.
  • Tropomyosin: Overlapping protein that covers binding sites on actin in relaxed muscles.
  • Troponin (TnC, TnT, TnI): Complex of three proteins that regulate muscle contraction by binding calcium ions and moving tropomyosin.

• Thick Filaments: Composed mainly of myosin molecules, responsible for generating muscle tension.

  • Myosin: Motor protein with a tail and head structure, functioning as a crossbridge during muscle contraction.
  • Myosin Tail: The elongated tail part of myosin that anchors it within the thick filament.
  • Myosin Head: The globular part of myosin that binds to actin to form crossbridges during contraction.

Neuromuscular Junction Components

• Synaptic Vesicles: Membrane-bound structures within nerve endings that store neurotransmitters, including acetylcholine.
• Synaptic Cleft: The small gap between the presynaptic terminal and the postsynaptic membrane, across which neurotransmitters diffuse.
• Motor End Plate: Specialized region of the muscle fiber plasma membrane that contains receptors for neurotransmitters.

Channels and Proteins

• Voltage Operated Channels: Ion channels that open or close in response to changes in membrane potential, critical for action potential propagation.
• Receptor Operated Channels: Ion channels that open in response to the binding of neurotransmitters, allowing ions to flow in or out.
• Calcium Channels: Specialized channels that allow calcium ions to enter the muscle cells, initiating contraction.
• Ca-ATPase: Enzyme that pumps calcium ions back into the sarcoplasmic reticulum post-contraction, essential for muscle relaxation.

Muscle Fiber Organization

• T Tubules: Extensions of the sarcolemma that penetrate into the muscle fiber, facilitating the rapid transmission of action potentials.
• Terminal Cisternae: Enlarged areas of the sarcoplasmic reticulum adjacent to T tubules, stores calcium ions for muscle contraction.
• Triads: Structural units consisting of a T tubule flanked by two terminal cisternae, important for the regulation of calcium release during muscle contraction.

Sarcomere Structure

• A Band: Dark band in the sarcomere consisting of thick filaments (myosin) and overlapping thin filaments.
• I Band: Light band in the sarcomere containing only thin filaments (actin).
• H Zone: Central region of the A band where thick filaments do not overlap with thin filaments during relaxation.
• M Line: Midpoint of the sarcomere, anchoring thick filaments together.
• Z Line: Boundary between adjacent sarcomeres, anchoring thin filaments and providing structure to the muscle fiber.

Miscellaneous

• Fascicle: A bundle of muscle fibers grouped together, surrounded by perimysium.
• Sarcomere: Functional unit of a muscle fiber, defined as the segment between two Z lines, responsible for muscle contraction mechanics.