zoo 106 lab muscular system

• Types of muscle tissues in the body

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle
• Muscle tissues


  • Elongated cells called fibers
  • Cytoplasm called sarcoplasm
  • Cell membrane called sarcolemma
• Skeletal muscle fibers


  • Long, cylindrical, multinucleated cells
  • Peripheral nuclei
  • Composed of subunits called myofibrils
  • Myofibrils composed of myofilaments of actin and myosin
• Myofibrils


  Extend the entire length of the muscle fiber
• Myofilaments


  Contractile thin protein actin and thick protein myosin
• Skeletal muscle sarcoplasm


  • Arrangement of actin and myosin filaments is very regular, forming distinct cross-striation patterns
  • Lighter-staining I bands and dark-staining A bands
• Cross-striations

  Skeletal muscle is also called striated muscle
• Sarcomere


  • Smallest structural and functional contractile unit of the muscle
  • Repeating contractile units seen along the entire length of each myofibril
  • Contains thick myosin filaments in the center and dark-staining A band
  • Contains thin actin filaments at the peripheries and light-staining I band
• Accessory proteins

  • Actin filaments bound to α-actinin, which binds them to the Z line
  • Thick myosin filaments anchored to the Z line by the protein titin
• Skeletal muscle structure


  • Surrounded by epimysium
  • Divided into fascicles by perimysium
  • Individual muscle fibers invested by endomysium
  • Blood vessels, nerves, and lymphatics located in connective tissue sheaths
  • Rich capillary plexus in endomysium
• skeletal muscles are attached to bones by tendons, which transmit force from the muscle to the bone
• Muscle contraction occurs when an action potential reaches the sarcolemma, causing calcium ion channels to open.
• the skeletal muscle is the most abundant tissue in mammals
• muscle fibers have striations due to sarcomeres that contain actin and myosin filaments
• Myosin heads attach to these exposed binding sites and form cross bridges with actin.
• Calcium ions diffuse out of the sarcoplasmic reticulum (SR) and bind to troponin on the thin filament, shifting tropomyosin and exposing binding sites on actin.
• Each fiber contains many myofibrils, which are composed of repeating contractile units called sarcomeres.
• The sliding filament theory states that during muscle contraction, thick and thin filaments slide past one another, shortening the length of the sarcomere.
• The sliding filament theory explains how skeletal muscle contracts during movement.
• The skeletal muscle consists of long cylindrical cells called muscle fibers or muscle cells that contain numerous nuclei.
• Each fiber contains many myofibrils, which are composed of repeating contractile units called sarcomeres.
• The sliding filament theory explains how skeletal muscle contracts during movement.
• Calcium ions diffuse out of the sarcoplasmic reticulum (SR) and bind to troponin on actin filaments, allowing myosin heads to attach to actin.
• Myosin heads detach from actin and reattach further down the actin filament, pulling it closer to the M line.
• Skeletal muscle cells can be classified into three types based on their structure and function: slow-twitch oxidative (Type I), fast-twitch oxidative glycolytic (Type IIa), and fast-twitch glycolytic (Type IIb).
• Myosin heads detach from actin and reattach further down the actin filament, pulling it closer to the M line.
• A single motor neuron innervates thousands of muscle fibers through its axonal branches.
• Myosin heads detach from actin and reattach further down the actin filament, pulling it closer to the M line.
• A single motor neuron innervates thousands of muscle fibers through its axonal branches.
• Skeletal muscle cells are multinucleated and can be up to several feet long.
• Muscles can be classified as either voluntary or involuntary based on their control by the nervous system.
• Muscles can be classified based on their location or function.
• Muscle fibers have two types of protein filaments - thick filaments made up of myosin molecules and thin filaments made up of actin molecules.
• Smooth muscles


  • No T tubules
  • Sarcoplasmic reticulum not well developed for storing much calcium
  • Exhibit numerous vesicular invaginations of the cell membrane called caveolae
• Caveolae


  May have the same function as the T tubules of striated muscles by controlling the influx of calcium into the cells following stimulation
• Smooth muscle contraction


  1. Calcium enters the sarcoplasm from the sarcoplasmic reticulum and from the cell membrane caveolae

  2. Calcium binds to calmodulin

  3. Calmodulin stimulates the interaction of actin and myosin

  4. Actin and myosin contract by a sliding filament mechanism

  5. Dense bodies are pulled closer together, producing contraction and shortening of the smooth muscle
• Smooth muscle


  • Dense bodies of neighboring cells are connected, allowing the smooth muscles to function as a unit
  • Exhibits spontaneous wavelike activity that passes in a slow, sustained contraction throughout the entire muscle
  • Produces a continuous contraction of low force and maintains tonus in hollow structures
• Peristaltic contractions in ureters, uterus, and digestive organs

  Contraction of smooth muscle propels the contents along the lengths of these organs
• Smooth muscle in arteries and other blood vessels

  • Regulates the luminal diameters
• Smooth muscle fibers

  • Make close contacts with each other via specialized gap junctions
  • Allow for rapid ionic communications between the smooth muscle fibers, resulting in coordinated activity in smooth muscle sheets or layers