Muscle

• Actin and myosin


  Tiny protein strands responsible for muscle contraction and relaxation
• Actin and myosin are responsible for all of your motions
• Muscle tissues turn chemical potential energy into mechanical energy by contracting and relaxing
• Types of muscle tissue

  • Smooth
  • Cardiac
  • Skeletal
• Smooth muscle tissue


  Found in the walls of hollow visceral organs, functions involuntarily
• Cardiac muscle


  Striated muscle tissue that functions involuntarily to keep blood pumping
• Skeletal muscles


  640 muscles that are mostly voluntary and striated
• Skeletal muscles attach to the skeleton and create movement by pulling bones
• Each skeletal muscle is technically its own organ
• Skeletal muscles are made up mostly of muscle tissue, connective tissue, blood vessels, and nerve fibers
• Muscle cells have their own personal nerve, artery, and vein
• Myofibrils


  Tiny, parallel threads that form muscle fibers
• Sarcomeres


  Segments within myofibrils that contain actin and myosin
• Z line


  Border formed by alternating thin filaments in a zigzag pattern
• A muscle contracting is about sarcomeres contracting, bringing Z-lines closer together
• Sliding filament model


  Describes how actin and myosin interact during muscle contraction
• Tropomyosin and troponin


  Proteins that block actin binding sites
• ATP is molecular currency that contains chemical energy
• Muscle cells have lots of nuclei and mitochondria
• Sarcoplasmic reticulum


  Specialized endoplasmic reticulum in muscle cells
• Sarcoplasmic reticulum contains calcium pumps and channels
• Muscle contraction process

  1. Action potential travels down motor neuron

  2. Releases acetylcholine

  3. Opens sodium channels

  4. Creates graded potential

  5. Triggers calcium release
• Calcium


  Essential for muscle contraction by binding to troponin
• Myosin binds to actin when the binding sites are exposed
• Myosin pulls on actin to contract the muscle
• Myosin releases ADP and phosphate after contracting
• Myosin binds to a new ATP molecule to release from actin
• Calcium pumps restock calcium in the sarcoplasmic reticulum
• Skeletal muscles are constructed like a rope made of bundles of protein fibers
• Actin and myosin myofilaments are the smallest strands in muscle tissue
• Calcium and ATP cause the binding and unbinding that makes sarcomeres contract and relax