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Muscles, The structure gets smaller this way (smallest<----largest) -…

- - - - myosin changes shape
        
        shape change causes the myosin head to swing
        
        a power stroke is produced
        
        the power stroke slides the actin past the myosin
        
        during contraction, the thin/thick filaments do not shorten
      - after excitation contraction coupling
    - - ATP is split into ADP and Pi, releasing energy to myosin and prepares the myosin head for activity
        
        Ca++ from SR binds to troponin C
        
        tropomyosin rolls off myosin binding sites found on actin
        
        powerstroke occurs when myosin head bends and the thin past the thick myofilament of myosin
        
        ADP and Pi are released from the myosin head
        
        A new ATP molecule binds to the myosin head
        
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        crossbridge forms
  - - - ac in NMJ spread over the sarcolemma down the T tubules into the core of the muscle cell
        
        because the ac is very close to the SR, Ca++ channels open
        
        Ca++ releases from the terminal cisternae of the SR
        
        Ca++ binds to troponin C on the thin myofilaments
        
        tropomyosin uncovers the myosin binding sites on actin
        
        myosin can now attach to the actin binding site to produce a power stroke
  - - - stiffness disappears after 24-48 hours hours
    - - myosin binds to actin forming the crossbridge between thin and thick filaments
        
        produces rigid condition of muscle
        
        cannot be broken without ATP or requires more cell degeneration to dissolve the linkage
- - - - one motor neuron can contract many muscle cells
        
        larger motor neurons can contact more muscle cells compared to smaller motor units which can only contact a few
        
        more muscle cells are required when performing more taxing action (i.e. hold a heavier object)
        
        results in a more forceful contraction
      - each muscle cell is activated by only 1 motor neuron
  - - - simplest and smallest muscle contraction
      - produced by 1 ac in the motor neuron
        
        causes release of just enough Ca++ in SR to cause a small contraction
      - lasts 10 to 100 ms
        
        latent period
        
        time delay from when ac occurs on the motor neuron and when the muscle actually contracts
        
        caused by events of the NMJ, generation of ac in the muscle cell and the interaction between thin/thick myofilaments
    - - causes the muscle tension to double
      - possible to add unlike ac because muscle twitches rely on protein interactions
      - high frequencies of ac produces a maximal tetanic contraction (tetanus)
        
        the plateau in muscle tension
        
        muscle contracts at faster rate
        
        causes stronger muscle contraction
- - - - muscle cells/fibers (Muscle cells and muscle fibers are the same
        
        myofibrils
        
        thin myofilaments
        
        contains globular protein actin(majority), troponin and tropomyosin
        
        each actin molecule has a special binding site for myosin
        
        actin
        
        similar structure to beads on a necklace and form the backbone of the thin myofilaments
        
        tropomyosin
        
        covers the binding sites of myosin when muscle is at rest
        
        troponin
        
        troponin A
        
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        troponin T
        
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        troponin C
        
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        at rest, this complex holds tropomyosin over the myosin binding sites
        
        how they work together
        
        thin/thick myofilament are in a alternating pattern along the myofibril
        
        they are also parallele to the myofibril and the muscle cell
        
        work together to perform a muscle contraction
        
        extends way from a central Z disk/line where they are attached
        
        one Z disk to another is a sarcomere
        
        smallest functional contractile unit of the muscle cell
        
        region with only thin filaments are called I bands
        
        thick myofilaments
        
        made up of the protein myosin(only)
        
        has 1 long bendable tail
        
        has 2 two heads
        
        can attach to myosin binding sites of actin
        
        has site that can split ATP which powers muscle contraction
        
        extends away from a central M line where they are attached
        
        region with only thick filaments are called A bands
- - - - surrounds the myofibrils
      - mesh-like network of tubes with Ca++ ions (These ions are required for contraction)
    - - found in the muscle cell
      - contains the thin/thick myofilaments
    - - small tube-like projections of the sarcolemma
      - extends down the cell to conduct ac deep into the cell where contractile proteins are found
    - - found at both ends of the SR and is close to the T tubules
      - is a continuation of the SR
    - - muscle cell membrane which the ac is trasmitted
- - - - special Ca++ pumps pump Ca++ back into the SR (active transport)
        
        with no Ca++, tropomyosin covers the myosin binding sites again, preventing myosin from binding to actin
        
        stops power stroke from occurring and muscle relaxes
      - as long as Ca++ is present, the muscle cannot relax and will contract