Muscle contraction

• What are skeletal muscles made of?

  Long muscle cells called muscle fibres
• What prefix is used for organelles inside muscle cells?

  Sarco
• What is the sarcolemma?

  Cell membrane of muscle cells
• What is the function of transverse tubules?

  Spread electrical impulses throughout the cell
• What is sarcoplasm?

  Cytoplasm of muscle cells
• What does the sarcoplasmic reticulum store?

  Calcium ions for muscle contraction
• What organelles are abundant in muscle cells for ATP production?

  Mitochondria
• What are myofibrils responsible for?

  Enabling contraction of muscle fibres
• What are myofibrils made of?

  Short units called sarcomeres
• What are the two types of myofilaments?

  Myosin and actin
• Why does actin appear as a light band?

  Because actin and myosin don’t overlap
• Why does myosin appear as a dark band?

  Because actin and myosin overlap
• What marks the end of each sarcomere?

  Z line
• What is the M-line?

  Middle region of the sarcomere
• What is the H-zone?

  Portion of A band with only myosin
• What characterizes slow twitch muscle fibers?

  Less powerful contraction, aerobic
• Why do slow twitch fibers have a reddish appearance?

  Due to high amounts of myoglobin
• What type of sports are slow twitch fibers made for?

  Endurance-based sports
• What characterizes fast twitch muscle fibers?

  Powerful contraction, fatigue easily
• What do fast twitch fibers store for energy?

  High concentration of glycogen
• What is the contraction-relaxation cycle of fast twitch fibers?

  Short contraction-relaxation cycle
• How do fast twitch fibers generate ATP?

  Mostly from anaerobic respiration
• What is the sliding filament theory?

  Myosin and actin move closer via sliding
• What happens to the sarcomere during contraction?

  It becomes shorter
• What blocks the actin-myosin binding site under resting conditions?

  Tropomyosin and troponin
• What triggers the release of Ca2+ from the sarcoplasmic reticulum?

  Wave of depolarization from action potential
• What happens when Ca2+ binds to troponin?

  Tropomyosin is pulled away from binding site
• What is the power stroke in muscle contraction?

  Myosin head pulls actin filament closer
• What happens during muscle relaxation?

  Ca2+ moves back into the sarcoplasmic reticulum
• What is the role of phosphocreatine in muscle cells?

  Regenerate ADP to ATP in anaerobic conditions
• What is produced during anaerobic respiration that leads to muscle fatigue?

  Lactic acid
• What are the differences between fast twitch and slow twitch muscle fibers?

  Fast Twitch:

  • Powerful contraction, fatigue easily
  • ATP from anaerobic respiration
  • Short contraction-relaxation cycle
  • Fewer capillaries, smaller mitochondria

  
  

  Slow Twitch:

  • Less powerful contraction, endurance-based
  • ATP from aerobic respiration
  • Long contraction-relaxation cycle
  • Denser capillaries, larger mitochondria
• What are the steps of muscle contraction according to the sliding filament theory?

  1. Myosin and actin slide closer together
  2. Sarcomere shortens
  3. Ca2+ binds to troponin, moving tropomyosin
  4. Myosin heads bind to actin, forming cross bridges
  5. ATP hydrolysis powers the movement of myosin heads
  6. Actin filaments are pulled closer to myosin
• What are the sources of ATP for muscle contraction?

  • Aerobic respiration: oxidative phosphorylation in mitochondria
  • Anaerobic respiration: glycolysis in cytoplasm, produces lactic acid
  • Phosphocreatine: regenerates ATP quickly for short bursts
• What happens to the I band during muscle contraction?

  It becomes narrower
• What happens to the Z-lines during muscle contraction?

  They move closer together
• What happens to the H-zone during muscle contraction?

  It becomes narrower
• What happens to the A-band during muscle contraction?

  It stays the same width
• How does ATP hydrolysis affect the actin-myosin cross bridge?

  It provides energy for breaking the cross bridge
• What is the role of tropomyosin in muscle contraction?

  It blocks the actin-myosin binding site