6.3.1 Structure of Skeletal Muscle

• Myofibrils are the primary site of muscle contraction within muscle fibers.


  True
• The sarcoplasmic reticulum stores and releases calcium ions for muscle contraction
• Match the organizational level with its surrounding structure:

  Muscle ↔️ Epimysium

  Fascicle ↔️ Perimysium

  Muscle Fiber (Cell) ↔️ Endomysium
• During muscle contraction, myosin heads pull actin filaments closer, shortening the sarcomere.


  True
• The boundaries of sarcomeres are called Z-lines
• What is the connective tissue layer that surrounds the entire muscle called?

  Epimysium
• Which structure within muscle fibers is the primary site of muscle contraction?

  Myofibril
• The sarcoplasmic reticulum (SR) stores and releases calcium ions
• What are the boundaries of a sarcomere called?

  Z-lines
• The sliding filament model explains how sarcomeres lengthen during relaxation

  False
• The epimysium surrounds the entire muscle
• Arrange the components of a skeletal muscle fiber in order from the outermost to the innermost structure:

  1️⃣ Sarcolemma

  2️⃣ Sarcoplasm

  3️⃣ Myofibrils
• T-tubules are invaginations of the sarcolemma that conduct action potentials deep into the muscle fiber.


  True
• Myofibrils are composed of sarcomeres, which contain the proteins actin and myosin
• Arrange the steps of the sliding filament model in the correct order:

  1️⃣ Myosin heads attach to actin

  2️⃣ Myosin heads pull actin filaments closer

  3️⃣ Myosin heads detach from actin

  4️⃣ Cycle repeats to shorten sarcomere
• Steps in the sliding filament model of muscle contraction

  1️⃣ Myosin heads attach to actin

  2️⃣ Myosin pulls actin filaments

  3️⃣ Sarcomere shortens

  4️⃣ Myosin heads detach

  5️⃣ Cycle repeats
• Fascicles, bundles of muscle fibers, are surrounded by perimysium
• The hierarchical organization of skeletal muscles allows for coordinated and efficient movements


  True
• T-tubules conduct action potentials deep into the muscle fiber

  True
• What is the structure of actin filaments within a sarcomere?

  Thin filaments attached to Z-lines
• Match the contractile protein with its function:

  Actin ↔️ Provides binding sites for myosin

  Myosin ↔️ Binds to actin and pulls filaments
• What does the perimysium organize within a muscle?

  Fascicles
• Match the organizational level of skeletal muscle with its structure and function:

  Muscle ↔️ Whole muscle organ, surrounded by epimysium ||| Contracts to produce movement

  Fascicle ↔️ Bundles of muscle fibers, surrounded by perimysium ||| Coordinates fiber contraction within a group

  Muscle Fiber (Cell) ↔️ Elongated muscle cells containing many nuclei, surrounded by endomysium ||| Carries out individual muscle contractions

  Myofibril ↔️ Contractile units within muscle fibers, made of sarcomeres ||| Primary site of muscle contraction
• What is the function of the sarcolemma in a muscle fiber?

  Conducts action potentials
• What are the boundaries of a sarcomere called?

  Z-lines
• What are the globular heads of myosin called?

  Cross-bridges
• The sliding filament model explains how sarcomeres lengthen during contraction

  False
• What connective tissue surrounds individual muscle fibers?

  Endomysium
• What is the outer plasma membrane of a muscle fiber called?

  Sarcolemma
• Which structures inside muscle fibers are responsible for contraction?

  Myofibrils
• Sarcomeres are repeating units within myofibrils and shorten during muscle contraction
• Steps in the interaction between actin and myosin during muscle contraction

  1️⃣ Myosin heads bind to actin

  2️⃣ Myosin pulls actin filaments

  3️⃣ Sarcomere shortens

  4️⃣ Myosin heads detach
• Connective tissue layers in skeletal muscles help distribute forces and maintain muscle shape


  True