The muscular system

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The muscular system

  1. 1. The Muscular System
  2. 2. There are 3 types of muscles
  3. 3. A. Function of Skeletal Muscles <ul><li>Produce movement </li></ul><ul><ul><li>Muscle pulls tendons to move the skeleton </li></ul></ul><ul><li>Maintain posture and body position </li></ul><ul><ul><li>Continuous muscle contraction </li></ul></ul><ul><li>Guard entrances and exits </li></ul><ul><ul><li>Encircle openings to digestive and urinary tracts. Control swallowing, defecation and urination </li></ul></ul><ul><li>Maintain body temperature </li></ul><ul><ul><li>Energy from contraction is converted to heat </li></ul></ul>
  4. 4. Skeletal Muscle <ul><li>Bundles are formed by: </li></ul><ul><li>epimysium epi = upon </li></ul><ul><li>perimysium peri = around </li></ul><ul><li>endomysium end = within </li></ul>
  5. 5. Terms <ul><li>Plasmalemma = Sarcolemma </li></ul><ul><li>Sarcoplasm = Cytoplasm </li></ul><ul><li>Sarcoplasmic Reticulum = Endoplasmic Reticulum </li></ul>
  6. 6. B. Anatomy of Skeletal Muscles - Gross Anatomy Surrounds muscle Divides muscle into compartments, each contain a bundle of muscle fibers called fascicle Bundle of muscle fibers Surrounds each muscle fiber, and tie adjacent fibers together All three layers attach muscle to bone
  7. 7. Myofibrils <ul><li>Cylinder as long as entire muscle fiber </li></ul><ul><li>Each fiber contains 100s to 1000s </li></ul><ul><li>Responsible for contraction </li></ul><ul><li>When myofibrils contract the whole cell contracts </li></ul><ul><li>Consist of proteins </li></ul><ul><ul><li>Actin – thin filaments </li></ul></ul><ul><ul><li>Myosin – thick filaments </li></ul></ul>
  8. 8. Connective Tissue Sheaths <ul><li>Connective Tissue of a Muscle </li></ul><ul><ul><li>Epimysium . Dense regular c.t. surrounding entire muscle </li></ul></ul><ul><ul><ul><li>Separates muscle from surrounding tissues and organs </li></ul></ul></ul><ul><ul><ul><li>Connected to the deep fascia </li></ul></ul></ul><ul><ul><li>Perimysium . Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle </li></ul></ul><ul><ul><ul><li>Contains b.v and nerves </li></ul></ul></ul><ul><ul><li>Endomysium . Loose connective tissue that surrounds individual muscle fibers </li></ul></ul><ul><ul><ul><li>Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue </li></ul></ul></ul><ul><li>Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis. </li></ul>
  9. 10. B. Anatomy of a Skeletal Muscle – Blood Vessels and Nerves <ul><li>Muscle contractions require energy </li></ul><ul><ul><li>Blood vessels deliver oxygen and nutrients to produce energy(ATP) </li></ul></ul><ul><li>Muscle contractions are under stimulation from the CNS(central nervous system) </li></ul>
  10. 11. Sarcomere <ul><li>Smallest functional unit of muscle fiber </li></ul><ul><li>Each myofibril contains 10,000 sarcomeres end to end </li></ul><ul><li>Interaction between thick and thin filaments cause contraction </li></ul><ul><li>Banded appearance </li></ul>
  11. 12. Sarcomeres: Z Disk to Z Disk <ul><li>Sarcomere - repeating functional units of a myofibril </li></ul><ul><ul><li>About 10,000 sarcomeres per myofibril, end to end </li></ul></ul><ul><ul><li>Each is about 2 µm long </li></ul></ul><ul><li>Differences in size, density, and distribution of thick and thin filaments gives the muscle fiber a banded or striated appearance. </li></ul><ul><ul><li>A bands: a dark band; full length of thick (myosin) filament </li></ul></ul><ul><ul><li>M line - protein to which myosins attach </li></ul></ul><ul><ul><li>H zone - thick but NO thin filaments </li></ul></ul><ul><ul><li>I bands: a light band; from Z disks to ends of thick filaments </li></ul></ul><ul><ul><ul><li>Thin but NO thick filaments </li></ul></ul></ul><ul><ul><ul><li>Extends from A band of one sarcomere to A band of the next sarcomere </li></ul></ul></ul><ul><ul><li>Z disk: filamentous network of protein. Serves as attachment for actin myofilaments </li></ul></ul><ul><ul><li>Titin filaments: elastic chains of amino acids; keep thick and thin filaments in proper alignment </li></ul></ul>
  12. 13. Microanatomy – Sarcolemma and T-Tubules <ul><li>Very large cells </li></ul><ul><li>100’s of nuclei </li></ul><ul><li>Cell membrane </li></ul><ul><li>pores open to T-tubules </li></ul><ul><li>Network of narrow tubules </li></ul><ul><li>filled with extracellular fluid </li></ul><ul><li>form passageways through muscle fiber </li></ul>
  13. 14. Sarcoplasmic Reticulum <ul><li>Specialized form of SER </li></ul><ul><li>Tubular network around each myofibril </li></ul><ul><li>In contact with T-Tubule </li></ul>
  14. 15. Sarcoplasmic Reticulum (SR) <ul><li>SR is an elaborate, smooth endoplasmic reticulum </li></ul><ul><ul><li>runs longitudinally and surrounds each myofibril </li></ul></ul><ul><ul><li>Form chambers called terminal cisternae on either side of the T-tubules </li></ul></ul><ul><li>A single T-tubule and the 2 terminal cisternae form a triad </li></ul><ul><li>SR stores Ca ++ when muscle not contracting </li></ul><ul><ul><li>When stimulated, calcium released into sarcoplasm </li></ul></ul><ul><ul><li>SR membrane has Ca ++ pumps that function to pump Ca ++ out of the sarcoplasm back into the SR after contraction </li></ul></ul>
  15. 16. Thick and Thin Filaments <ul><li>Thin </li></ul><ul><ul><li>twisted actin molecules </li></ul></ul><ul><ul><li>Each has an active site where they interact with myosin </li></ul></ul><ul><ul><li>Resting – active site covered by tropomyosin which is held in place by troponin </li></ul></ul><ul><li>Thick </li></ul><ul><ul><li>Myosin </li></ul></ul><ul><ul><li>Head attaches to actin during contraction </li></ul></ul><ul><ul><li>Can only happen if troponin changes position, moving tropomyosin to expose active site </li></ul></ul>
  16. 17. Muscle Fiber Anatomy <ul><li>Sarcolemma - cell membrane </li></ul><ul><ul><li>Surrounds the sarcoplasm (cytoplasm of fiber) </li></ul></ul><ul><ul><ul><li>Contains many of the same organelles seen in other cells </li></ul></ul></ul><ul><ul><ul><li>An abundance of the oxygen-binding protein myoglobin </li></ul></ul></ul><ul><ul><li>Punctuated by openings called the transverse tubules (T-tubules) </li></ul></ul><ul><ul><ul><li>Narrow tubes that extend into the sarcoplasm at right angles to the surface </li></ul></ul></ul><ul><ul><ul><li>Filled with extracellular fluid </li></ul></ul></ul><ul><li>Myofibrils -cylindrical structures within muscle fiber </li></ul><ul><ul><li>Are bundles of protein filaments (= myofilaments ) </li></ul></ul><ul><ul><ul><li>Two types of myofilaments </li></ul></ul></ul><ul><ul><ul><ul><li>Actin filaments (thin filaments) </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Myosin filaments (thick filaments) </li></ul></ul></ul></ul><ul><ul><li>At each end of the fiber, myofibrils are anchored to the inner surface of the sarcolemma </li></ul></ul><ul><ul><li>When myofibril shortens, muscle shortens (contracts) </li></ul></ul>
  17. 18. Structure of Actin and Myosin
  18. 19. Myosin (Thick) Myofilament <ul><li>Many elongated myosin molecules shaped like golf clubs. </li></ul><ul><li>Single filament contains roughly 300 myosin molecules </li></ul><ul><li>Molecule consists of two heavy myosin molecules wound together to form a rod portion lying parallel to the myosin myofilament and two heads that extend laterally. </li></ul><ul><li>Myosin heads </li></ul><ul><ul><li>Can bind to active sites on the actin molecules to form cross-bridges. (Actin binding site) </li></ul></ul><ul><ul><li>Attached to the rod portion by a hinge region that can bend and straighten during contraction. </li></ul></ul><ul><ul><li>Have ATPase activity: activity that breaks down adenosine triphosphate (ATP), releasing energy. Part of the energy is used to bend the hinge region of the myosin molecule during contraction </li></ul></ul>
  19. 20. Sliding Filament Model of Contraction <ul><li>Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree </li></ul><ul><li>In the relaxed state, thin and thick filaments overlap only slightly </li></ul><ul><li>Upon stimulation, myosin heads bind to actin and sliding begins </li></ul>
  20. 21. Sliding Filament Model of Contraction <ul><li>Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere </li></ul><ul><li>As this event occurs throughout the sarcomeres, the muscle shortens </li></ul>InterActive Physiology ® : Muscular System: Sliding Filament Theory PLAY
  21. 22. Sliding Filaments and Cross Bridges <ul><li>Sarcomere contraction – Sliding Filament Theory </li></ul><ul><ul><li>Thin filaments slide toward center of sarcomere </li></ul></ul><ul><ul><li>Thick filaments are stationary </li></ul></ul><ul><ul><li>Myosin head attaches to active site on actin (cross bridge) </li></ul></ul><ul><ul><li>Pull actin towards center, then detaches </li></ul></ul>
  22. 23. Questions <ul><li>How would severing the tendon attached to a muscle affect the ability of the muscle to move a body part? </li></ul><ul><li>Why does skeletal muscle appear striated when viewed through a microscope? </li></ul><ul><li>Where would you expect the greatest concentration of calcium ions in resting skeletal muscles to be? </li></ul>
  23. 24. Control of Muscle Fiber Contraction Under control of the nervous system
  24. 25. <ul><li>Electrical signal travels to the muscle. </li></ul><ul><li>Electrical signal spreads over entire sarcolemma, down t-tubules to sarcoplasmic reticulum </li></ul><ul><li>Sarcoplasmic reticulum releases massive amounts of calcium </li></ul><ul><li>Increase in calcium – sarcomeres contract </li></ul>
  25. 26. The Contraction Cycle <ul><li>Step 1 </li></ul><ul><ul><li>Ca+ binds to troponin, changing the tropomyosin position, in turn exposing active site on actin </li></ul></ul><ul><li>Step 2 </li></ul><ul><ul><li>Myosin head attaches to actin </li></ul></ul><ul><li>Step 3 </li></ul><ul><ul><li>Pulling of actin towards center of sarcomere </li></ul></ul><ul><li>Step 4 </li></ul><ul><ul><li>Detachment of cross bridge </li></ul></ul>
  26. 27. <ul><li>How would a drug that interferes with cross-bridge formation affect muscle contraction? </li></ul><ul><li>What would you expect to happen to a resting skeletal muscle if the sarcolemma suddenly became very permeable to calcium ions? </li></ul>Questions

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