Skeletal

• How many different muscles do humans have?

  Over 650 different muscles
• What are the main components of skeletal muscle structure?

  • Myonuclei on the perimeter of muscle fibers
  • Two ends attached to bones via tendons
  • Surrounded by connective tissue (Epimysium)
  • Organized into fascicles separated by Perimysium
  • Individual muscle cells (myofibres) surrounded by Endomysium
• What is the plasma membrane of skeletal muscle called?

  Sarcolemma
• What is the function of T-tubules in skeletal muscle?

  1. tubules are invaginations of the sarcolemma that extend deep into the muscle fiber
• What surrounds each myofibril in skeletal muscle?

  The sarcoplasmic reticulum (SR)
• What is the term for the region where one T-tubule is flanked by two terminal cisternae?

  Triad
• What are the key features of a skeletal muscle cell (muscle fiber)?

  • Myofibrils made of contractile filaments
  • Contains nucleus, mitochondria, and cytosol
  • Striated appearance due to actin and myosin
• What are the components of a myofibril?

  • Actin (thin filaments)
  • Myosin (thick filaments)
  • A Band (dark region of thick filaments)
  • I Band (light region of thin filaments)
  • Z line (bisects I band)
  • H Zone (region with only thick filaments)
  • M line (middle of A band)
  • Sarcomere (unit of contraction)
• What is the Sliding Filament Theory in muscle contraction?

  It describes how muscle contraction requires ATP, Ca$^{2+}$, thick and thin filaments, tropomyosin, and troponin
• What mnemonic can be used to remember the components required for muscle contraction?

  ACT-4
• What is the role of myosin in muscle contraction?

  Myosin makes thick filaments and has a globular head and long tail
• What happens to the myosin binding site on actin during muscle contraction?

  Tropomyosin moves off the myosin binding site when Ca$^{2+}$ binds to troponin
• What is the cross-bridge cycle in muscle contraction?

  • Actin filaments bound to the Z line
  • Thin filaments kept in order by nebulin
  • Thick filaments made of myosin with heads facing Z line
  • Thick filaments kept linear by titin
• What is the force-length relationship in muscle physiology?

  Titin is mostly responsible for passive force production
• What are the two main types of muscle fibers?

  • Slow-twitch (type I): red, aerobic, high fatigue resistance
  • Fast-twitch (type II): white, glycolytic, low fatigue resistance
• What is the characteristic of slow-twitch muscle fibers?

  They are red, small, easily excitable, and aerobic
• What is the characteristic of fast-twitch muscle fibers?

  They are white, have high glycogen, and low myoglobin
• What are the properties of type IIA muscle fibers?

  • Intermediate properties
  • Aerobic with high myoglobin
• What is muscle plasticity?

  • Changes in muscle fiber types due to training
  • Cross-innervation effects
  • Adaptation to damage
• What is the effect of eccentric exercise on muscle?

  Muscle lengthens during active force generation
• What are the diseases associated with muscle loss?

  • Muscular Dystrophy
  • Muscular Atrophy
  • Metabolic conditions (e.g., Type II Diabetes)
  • Aging (sarcopenia)
  • Cancer (cachexia)
• What is sarcopenia?


  Loss of muscle mass during aging
• What is the percentage of muscle mass loss between ages 50-90?

  ~50% loss
• What are some mechanisms of aging that affect muscle mass?

  Motor neuron death, fast-twitch fiber atrophy, and lowered response to anabolic stimuli
• What is the effect of weight training in humans aged 90+?

  It can help maintain muscle mass and strength
• What are the effects of muscle denervation?

  • Loss of muscle function
  • Changes in muscle fiber composition
  • Potential for recovery with electrical stimulation
• What is cachexia?


  Severe wasting of the body due to chronic illness
• What is a possible mechanism of cachexia in cancer patients?

  Cytokine secretion by tumor/inflammatory cells activates muscle protein degradation
• What is myostatin and its role in muscle physiology?

  • Myostatin is a negative regulator of muscle growth
  • Inhibition can lead to increased muscle mass
  • Relevant in conditions like muscular dystrophy and cachexia
• Who described Duchenne Muscular Dystrophy and when?

  Guillaume Duchenne in 1868
• What are the phases of Duchenne Muscular Dystrophy (DMD)?

  • Early
  • Intermediate
  • Late
• What is the role of dystrophin in muscle fibers?

  • Stabilizes muscle fibers
  • Connects the cytoskeleton to the extracellular matrix
  • Loss of dystrophin leads to muscle degeneration
• How do type 2 muscle fibers respond to damage?

  Type 2 fibers are more sensitive to damage and degeneration
• What is the title of the study by Willcocks et al. (2016)?

  Dystrophy Pathology
• What are the phases of Duchenne Muscular Dystrophy (DMD)?

  • Early
  • Intermediate
  • Late
• What is the role of dystrophin in muscle cells?

  Dystrophin stabilizes muscle fibers.
• What are the types of muscle fibers affected in DMD?

  • Dystrophin Positive Muscle Fibres
  • Revertant Fibres
  • Type 2 fibres are more sensitive to damage/degeneration
• What happens to muscle fibers during eccentric contractions in DMD?

  There is a greater loss of force and more fiber membrane damage.
• What type of genetic disorder is Duchenne Muscular Dystrophy (DMD)?

  1. linked recessive disorder
• What is the incidence of DMD?

  Approximately 1 in 3500 live male births