6.3.2 Mechanism of Muscle Contraction

• Inside the muscle fiber, the sarcoplasmic reticulum stores calcium
• What type of filament is made of actin molecules?

  Thin
• The sliding filament mechanism results in the shortening of the sarcomere.


  True
• In the sliding filament theory, what do myosin heads bind to form cross-bridges?

  Actin
• Which protein creates cross-bridges to pull actin filaments?

  Myosin
• The sliding filament theory explains how muscle contraction is driven by the sliding of actin and myosin
• The cross-bridges pull the actin filaments past the myosin filaments, shortening the sarcomere
• Actin filaments are thicker than myosin filaments.

  False
• The sliding filament theory explains how muscle contraction occurs.


  True
• The myosin heads pull the actin filaments towards the center of the sarcomere.
• Excitation-contraction coupling converts electrical stimulation into muscle contraction.


  True
• A motor neuron releases acetylcholine at the neuromuscular junction.
• Calcium ions bind to troponin, which moves tropomyosin away from actin binding sites.
• ATP is required for muscle relaxation to transport calcium back into the sarcoplasmic reticulum.


  True
• The sarcolemma contains T-tubules, which conduct electrical signals deep into the fiber.
• Actin filaments are thin, helical structures composed of actin molecules
• What are the two types of filaments in muscle cells responsible for contraction?

  Actin and myosin
• Which structure in muscle cells stores calcium ions?

  Sarcoplasmic reticulum
• Myosin filaments are thin and actin filaments are thick.

  False
• Myosin filaments consist of myosin molecules with a head and a tail
• What theory explains how muscle contraction occurs through the sliding of actin and myosin filaments?

  Sliding filament theory
• ATP binding to myosin heads causes them to detach from actin filaments.


  True
• What process converts electrical stimulation into muscle contraction?

  Excitation-contraction coupling
• Calcium ions released from the sarcoplasmic reticulum bind to troponin.


  True
• What is the process by which a muscle returns to its resting state after contraction?

  Muscle relaxation
• Myosin heads detach from actin filaments due to the absence of calcium.

  True
• What is the immediate source of energy for muscle contraction?

  ATP
• ATP provides energy for prolonged muscle activity.

  False
• What is the cell membrane of a skeletal muscle fiber called?

  Sarcolemma
• Sarcomeres are the main contractile units of muscle fibers.


  True
• The process by which myosin heads bind to actin is called forming cross-bridges
• Match the feature with the correct filament:

  Thin filament ↔️ Actin

  Thick filament ↔️ Myosin
• Steps of the sliding filament theory:

  1️⃣ Myosin heads bind to actin

  2️⃣ Cross-bridges are formed

  3️⃣ Myosin heads pull actin filaments

  4️⃣ Sarcomere shortens
• The sliding filament theory explains how myosin heads pull actin filaments.


  True
• During contraction, myosin heads bind to actin, forming cross-bridges
• The mechanism of muscle contraction is known as the sliding filament theory
• Actin filaments are composed of actin molecules
• Myosin heads bind to actin filaments, forming cross-bridges
• Myosin filaments are thin and actin filaments are thick.

  False
• Steps in excitation-contraction coupling

  1️⃣ Motor neuron releases acetylcholine

  2️⃣ Action potential travels across sarcolemma and T-tubules

  3️⃣ Calcium ions released from sarcoplasmic reticulum

  4️⃣ Calcium binds to troponin, exposing actin binding sites

  5️⃣ Myosin heads form cross-bridges with actin

  6️⃣ Sliding filament mechanism shortens sarcomere