Skeletal System

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Siobhan
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130823
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Skeletal System
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2012-02-05 12:09:28
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Skeletal System
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Skeletal System
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  1. 3 types of muscles of vertebrates
    • 1) Skeletal muscle appears striated voluntary, or conscious, control
    • 2) Cardiac muscle- also striated, located only in the heart Involuntary control
    • 3) Smooth muscle- not striated
    • Involuntary control

  2. structures of skeletal muscle
    myofibrils, saroplasmic reticulum, T tubukes, sarcomere, z line, actin, myosin
  3. sarcoplasmic reticulum
    • SR stores calcium, important for contraction
    • surrounds each myofibril
  4. T tubules
    • encircle the myofibrils
  5. Sarcomere
    unit of a myofibril
  6. Z lines
    • connect sarcomeres
  7. Actin
    thin filaments, attach to Z line
  8. Myosin
    • thick filaments

  9. How Do Skeletal Muscles Contract?
    • Relaxed muscle: tropomyosin prevents the myosin heads from attaching to actin
    • Contracting muscle:
    • tropomyosin moves, allowing myosin to bind to actin
    • All sarcomeres of a muscle fiber shorten at the time
    • ATP is required to extend myosin (sling shot)
  10. Sliding Filament mechanism of muscle contraction
    • 1. Tropomyosin covers the binding sites, so the myosin head cannot attatch.
    • 2. When the binding sites of actin are exposed, the byosin head attaches to a bind site
    • 3. The myosin head flexes, pulling the thin filament past the thick filament and shortening the sarcomere
    • 4. Using energy from ATP, the myosin head detaches from actin, extends, and then attaches to another actin binding site farther along on the thin filament

  11. All vertebrate neuromuscular junctions use the neurotransmitter acetylcholine
    • Each action potential in a motor neuron releases enough acetylcholine to produce a huge excitatory postsynaptic potential in the muscle fiber, bringing its membrane potential above threshold and triggering an action potential

    • Axons stimulate muscle fibers at neuromuscular junctions (synapse)

    Acetylcholine is the neurotransmitter that triggers the action potential

    The action potential moves down the T tubules

    to the SR

    where it causes calcium ions (Ca2+) to be released from the SR

    Ca2+ binds to troponin, causing it to pull tropomyosin, off the actin binding sites

    • myosin heads can bind to actin

  12. What makes the fiber stop contracting?
    • When the action potential in the muscle fiber is over, the SR stops releasing Ca2+

    Active transport (req ATP) pump Ca2+ back into the SR

    Ca2+ leaves the accessory proteins, which move back over the active binding sites

    • Therefore, the myosin head can no longer attach to actin, and contraction stops within a few hundredths of a second

  13. Muscle Contractions
    • motor unit : A motor neuron and all the muscle fibers that it innervates
    • Strength: varies in both the number of muscle fibers stimulated and the frequency of action potentials in each fiber
    • Slow twitch: less power, lasts longer, lots of mitochondria, good blood supply, more ATP, less fatigue. Thin fibers, fewer myofibrils (marathon runner)
    • Fast twitch: more powerful, smaller blood supply, few mitochondria, uses mostly glycolysis. Thick fibers, more myofibrils. (sprinter)

  14. 40.4 How Do Cardiac and Smooth Muscles Differ From Skeletal Muscle?
    • Cardiac muscle powers the heart
    • Single nucleus, striated, intercalated disks
    • contract around 70 times each minute, enormous numbers of mitochondria
    • Action potentials from the pacemaker spread rapidly through gap junctions in the intercalated discs, help together by desmosomes
  15. Smooth Muscle
    • surrounds blood vessels and most hollow organs, including the uterus and bladder
    • not striated because the thin and thick filaments are scattered throughout the cells
    • single nucleus
    • stretches easily, (bladder, stomach, uterus)
    • can be initiated by stretching, by hormones, by signals from the autonomic nervous system, or by a combination of these stimuli
    • produces slow, involuntary contraction

  16. 40.5 What Are the Functions and Structures of Vertebrate Skeletons?
    • The skeleton provides a rigid framework that supports the body and protects its internal organs
    • brain and spinal cord are almost completely enclosed
    • rib cage protects the lungs and the heart
    • pelvic girdle supports and protects abdominal organs
  17. Vertebrae Skeleton
    • allows locomotion: adapted for walking, running, jumping, etc
    • Sensory function: bones of the middle ear transmit sound
    • Blood production: red blood cells, white blood cells, and platelets in red bone marrow (sternum ribs, upper arms and legs, and hips)
    • Stores calcium and phosphorus: maintaining a constant concentration in the blood






  18. 2 types of skeleton
    • The axial skeleton: includes the bones of head, vertebral column, and rib cage
    • The appendicular skeleton: includes the pectoral and pelvic girdles, and the appendages attached to them

  19. 3 types of ct in bone
    cartilage, bone, ligaments
  20. Cartilage
    • During the embryonic development of the skeleton, except for the skull and collarbone, is first formed from cartilage
    • also covers the ends of bones at joints
    • nose ears, larynx, trachea, and bronchi
    • tough, shock-absorbing intervertebral discs
    • The living cells of cartilage: chondrocytes
    • Blood vessels do not penetrate, therefore very slow to repair if at all
  21. Bone
    • hard outer shell of compact bone that encloses spongy bone in its interior
    • Compact bone is dense and strong and provides an attachment site for muscle
    • Spongy bone consists of an open network of bony fibers
    • It is porous, lightweight, rich in blood vessels
    • Contains bone marrow, where blood cells form


  22. There are three types of bone cells:
    • Osteoblasts—bone-forming cells
    • Osteocytes—mature bone cells
    • Osteoclasts—bone-dissolving cell

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