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Lecture 9 - Skeletal I

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Terms in this set (21)

  • Major functions of the musculoskeletal system
    Body movement, moving substances (blood, lymph), maintaining posture, generating heat (thermogenesis), and storing energy as glycogen.
  • Connective tissues associated with skeletal muscle
    Tendon attaches muscle to bone, ligament attaches bone to bone, and bone provides structural support.
  • Four key properties of skeletal muscle
    Excitability (respond to stimuli), contractility (generate tension), extensibility (stretch without damage), and elasticity (return to original shape).
  • Definition of a muscle fascicle
    A bundle of 10-100 muscle cells (fibers) wrapped in connective tissue composed mainly of collagen fibers.
  • Characteristics of a skeletal muscle fiber
    A single skeletal muscle cell, very long (4-12 inches), multinucleated syncytium packed with contractile proteins called myofibrils.
  • Role of satellite cells in skeletal muscle
    Adult stem cells on the muscle fiber periphery that support growth, repair, and regeneration of muscle tissue.
  • Major components of a skeletal muscle cell
    Includes the sarcolemma (cell membrane), T-tubules (membrane invaginations), sarcoplasmic reticulum (Ca++ storage), myofibrils, glycogen, myoglobin, mitochondria, and nuclei.
  • Definition of a sarcomere
    The functional contractile unit of muscle, defined as the segment between two Z discs, containing thick and thin filaments.
  • Structural regions within a sarcomere
    A band: length of thick filaments, H band: thick filaments only, I band: thin filaments only, M line: holds thick filaments together.
  • Composition of thick filaments
    Made of ~300 myosin proteins with ATPase activity that converts chemical energy from ATP into mechanical energy.
  • Composition of thin filaments
    Consist of actin (G actin and F actin), tropomyosin (blocks myosin binding sites), and troponin (binds tropomyosin, actin, and Ca++).
  • Functions of giant accessory proteins in muscle
    Nebulin aligns actin, titin provides elasticity and stabilizes myosin, and dystrophin links myofibrils to the cell membrane.
  • Role of dystrophin in skeletal muscle
    Links myofibrils to the cell membrane, maintaining muscle cell integrity during contraction.
  • Sliding filament model of muscle contraction
    Thick and thin filaments slide past each other; thick filaments pull thin filaments toward the M line, shortening the sarcomere without changing filament length.
  • Changes in sarcomere bands during contraction
    A band width remains constant, while H band and I band widths narrow as filaments slide.
  • Definition of a motor unit
    A somatic motor neuron and all the skeletal muscle fibers it innervates, contracting in unison.
  • Neuromuscular junction (NMJ) components
    Includes the motor end plate (muscle membrane with ACh receptors), synaptic end bulb of the neuron, and Schwann cell terminal glia.
  • Sequence of events at the NMJ to initiate muscle action potential
    1) ACh release, 2) ACh binds receptors, 3) end plate potential, 4) local ion flow, 5) muscle action potential, 6) ACh degraded by acetylcholinesterase.
  • Role of T-tubules and DHP receptors in excitation-contraction coupling
    Muscle action potential travels down T-tubules; DHP receptors sense voltage and open RyR Ca++ channels in the sarcoplasmic reticulum.
  • How contraction ends during muscle relaxation
    Ca++ is actively pumped back into the sarcoplasmic reticulum by Ca++ ATPase, reducing cytosolic Ca++ and stopping contraction.
  • Definition of a muscle twitch
    A single cycle of contraction and relaxation in a muscle fiber following one action potential.