Muscle Cells

Muscle Cells

Characteristics of muscles
1. responsiveness/excitability
  1. Conductivity
    1. Contractility
      1. Extensibility
        elasticity
        returns to original resting length after being stretched.
        can be stretched between contractions
      2. shortens when stimulated
    2. local electrical change triggers a wave of excitation, travels along muscle fiber.
  2. responds to chemical signals, stretch and electrical changes across plasma membrane
Connective Tissue Elements
1. Tendons
  1. Endomysium
    1. Perimysium
      1. epimysium
        con tissue surrounds entire muscle.
        continuous with collagen fibers of tendon
      2. connec tissue around muscle fascicles
    2. connec tissue AROUND muscle cells
  2. tendons are attachments between muscle and bone matrix
The Muscle Fiber
1. Sarcolemma
  1. Sarcoplasm
    1. Myofibrils
      1. Multiple nuclei
        mitochondria
        SR sarcoplasmic reticulum
        tubules
        triad
        a T tubule and two terminal cisterns
        tubular infoldings of sarcolemma penetrates through the cell and exists other side
        release of Ca2+ into cell
        smooth ER forms network around each myofibril
        calcium reservoir needed to contract
        packed in between myofibrils to produce ATP
        flat nuclei pressed against inside of sarcolemma
      2. long protein bundles occupies the main portion of sarcoplam
        Glycogen
        stored in abudance, long chain of glucsoe, provides energy with heightened exercise.
        myoglobin
        red pigment, stores oxygen to produce ATP
    2. cytoplasm of m. fiber
  2. plasma membrane of m. fiber.
Myofiliments
1. each myofibril is a bundle of parallel protein microfilaments called myofilaments
2. 3 kinds of Myofilaments
  1. Thick filament= Myosin
    1. hundreds of myosin molecules
      1. shaped like a golf club 2 chains intertwined forms a shaft like tail, double globular head
        myosin heads are cross bridges attaches to actin and pulls it with regular movement.
  2. Thin filament= Actin
    1. Fibrous (F) actin; two intertwined strands. string of globular (G) actin submunits
      1. string of globular (G) actin subunits each with an active site, binds to head of myosin molecule.
      2. like a double strand of pearls.
      3. Tropomyosin molecules each blocking 6-7 active sites on G actin subunits
        Troponin molecule- small, calcium-binding protein , a calcium receptor on each tropomyosin molecule
        needs calcium or it wont bind.
  3. Elastic Myofilaments
    1. Titin
      1. made of protien (connectin)
        Huge springy protein
        helps stabilize thick filament=myosin
        prevents over stretchin
3. contractile proteins
  1. myosin and actin are called contractile proteins they shorten the muscle fiber.
4. Regulatory Proteins
  1. troponin and topomyosin act like a switch to determine when fiber can contract and when it can't
    1. contraction activated by rels of calcium into sarcoplasm and its binding to troponin
      1. troponin changes shape and move topomyosin off the active sites on actin
Striations
1. myosin and actin are proteins that occur in all cells
  1. function in cellular motility, mitosis, transport of intracellular material
    1. organized in a precise way in skeletal and cardiac muscles.
      1. A band= anisotropic. protein is myosin
        part of A band where thick and thin filaments overlap
        H band in the middle of A band, these are thick filaments
        M line is in the middle of the H band
      2. I band= isotropic. protein is actin.
        alternating lighter band the way the bands reflect polarized light
      3. Z Disc
        provides anchorage for thin filaments and elastic filaments
        Sarcomere
        the segment of the myofibril one z disc to the next is one sarcomere

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	Created by dancedrill over 11 years ago

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