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Skeletal Muscle Tissue Contraction by v84g8v

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									Skeletal Muscle Tissue
     Contraction

         Chapter 10
  Anatomy and Physiology
        Mr. Knowles
 Liberty Senior High School
  A Brief Review of Skeletal
        Muscle Tissue
  Connective Tissue        Structures
• Epimysium           Entire muscle from
  separates the…       other tissue.

• Perimysium divides Bundles of muscle
  the muscle into…    fibers- fascicles.

• Endomysium          Individual skeletal
  surrounds the…        muscle fibers.
 How does a skeletal
muscle cell differ from
most other eukaryotic
        cells?
              A Comparison
         Most Cells             Skeletal Muscle
•   Small; < 100 μm long •    Large; 12 inches long
•   One Nucleus           •   Multiple Nuclei
•   Normal metabolism- •      High metabolism-
    needs normal enzymes;     needs more enzymes;
    one copy of genes.        more genes.
•   100’s of mitochondria •   1,000’s of mitochond.
•   Endoplasmic Reticulum •   Sarcoplasmic
•   No myofibrils             Reticulum
                          •   Myofibrils
          Sarcolemma

           Sarcoplasm




Nucleus
 Special Terms for Muscle Fibers
• Sarcoplasm- cytoplasm of a muscle
  fiber.
• Sarcolemma- unique cell membrane
  of a muscle fiber.
• The sarcolemma forms tubes that
  travel into sarcoplasm at right angles-
  Transverse Tubules (T tubules).
• Action Potentials (unequal charges)
  travel down these T tubules.
    Inside a Muscle Fiber…
• Each T tubule encircles cylindrical
  structures- myofibrils.
• Myofibrils- 1-2 μm in diameter and as
  long as entire cell. 100’s – 1,000’s of
  myofibrils/cell.
• Myofibrils – are bundles of
  myofilaments – 2 kinds of protein
  filaments called actin (thin filaments)
  and myosin (thick filaments).
   Inside the muscle fiber…
• Myofibrils can shorten and contract the
  muscle fiber.
• Myofibrils are attached to the
  sarcolemma on its inner surface.
• Collagen fibers are attached to the
  sarcolemma on its outer surface. These
  fibers extend into the tendon.
• Myofibrils  pull on sarcolemma 
  pulls on tendon  muscle contraction.
Muscle Fiber
                  Sarcolemma
                        Tendon
     Myofibrils


                  Collagen


Intracellular      Extracellular
Triad
        Terminal
        Cisternae




  T Tubule
    Sarcoplasmic Reticulum
• Pumps Ca+2 out of the sarcoplasm and
  stores it.
• The resting cell has very little Ca+2 in the
  sarcoplasm. 1000X more Ca+2 in the SR
  than in the sarcoplasm.
• The SR is made up of terminal cisternae
  that lie on above the junction of thin and
  thick filaments in the sarcomeres.
    The Organization of the
          Myofibril
• Myofilaments are organized into
  repeating functional units-
  Sarcomere- smallest functional unit
  of the fiber.
• Sarcomere = myosin + actin + other
  stabilizing proteins.
Fig. 10-3.
P. 282
     Inside the Sarcomere…
• Have two regions or Bands:
  1. A Bands- are dArk bands and have
  three parts.
      a. M line- a protein that connects
  neighboring thick filaments, keeps their
  position.
      b. H zone- a region with only thick
  filaments.
      c. Zone of Overlap- thin and thick
  filaments overlap.
     Inside the Sarcomere…
• Have two Bands:
     2. I Bands- are lIght bands; only find
  thin filaments.
     a. Z lines- mark the boundaries
  between the adjacent sarcomeres on the
  myofibril; have connectin – a connecting
  protein that interconnects thin filaments.
     b. Titin- a protein that aligns thick and
  thin filaments; resist extreme stretching.
     Z Line




A Band    I Band
Z lines
    Thin Filaments (Actin)
Contains three proteins:
• F actin- a twisted strand of 300-400
  globular (G) actin molecules.
  – Each G actin has an active site- a
    region where thick filaments can
    bind.
• Tropomyosin are strands of protein
  that wrap around F actin. They cover
  the active site. This prevents actin-
  myosin interaction.
    Thin Filaments (Actin)
• Troponin- three globular subunits (parts).
  – One subunit binds to tropomyosin and
    locks the two together.
  – Another subunit binds to a G actin
    molecule, holding troponin and
    tropomyosin to the actin.
  – The third subunit binds to a Ca+2 ion.
    Resting cells have low Ca+2 and so this
    subunit is empty in the resting cell.
  Thick Filaments (Myosin)
• Made of 500 myosin molecules.
• Each myosin – two subunits twisted
  around each other.
• Myosin has a long, attached tail
  bound to other myosin molecules in
  the thick filament.
   Thick Filaments (Myosin)
• The free head projects outward, toward
  the nearest thin filament. Head can bind
  to the active site on the G actin.
• Between the head and the tail there is a
  flexible hinge that lets the head swing
  back and forth.
• All myosin molecules are arranged with
  their tails pointing toward the M line.
   Supporting the Myofibrils
• Desmin- is a complex network of
  protein that twists around each Z line
  and connects adjacent myofibrils.
• Vertical bands of desmin can be seen
  with a light microscope and give the
  fiber a banded appearance-striated
  muscle.
      The
Sliding Filament
     Theory
An explanation of how
 skeletal muscle cells
       contract.

								
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