Skeletal muscle

Skeletal muscle

1. Anatomy

   • Histology
     • Connective tissue(1)
       • Epimysium - surrounds muscle
         • dense irregular connective tissue
         • Perimysium - surrounds fascicle
           • dense irregular connective tissue
           • Endomysium - surrounds muscle fiber
             • areolar connective tissue
     • Muscle tissue(6)
       • Skeletal muscle tissue (voluntary & striated)
         • Myofiber (cell)
           • Myofibrils
             • Sacromere (contractile unit)
               • Myofilaments
                 • thick (myosin molecules)
                   • attached to elastic protein titin
                 • thin (actin + regulatory proteins)
                   • tropomyosin
                   • troponin
                 • between 2 Z-lines
           • Sarcoplasm (cytoplasm)
             • glycosomes
               • stores glycogen
             • myoglobin
               • stores oxygen
           • Sarcolemma (plasma membrane)
           • Sarcoplasmic reticulum
             • regulates Ca ions
   • Muscle
     • Fascicle
   • Orbicularis oris
     • Origin
       • Maxilla (upper jaw and palate) and mandible (lower jaw) bones
     • Insertion
       • Muscle fibres from the opposite sides meet each other along the midline between nose and lips and merge with the skin.
     • Action
       • Comresses/puckers the lips
       • modifies movement of other facial muscles attached to it
     • Classification
       • Believed to be a sphincter
         • Group of 4 muscles in circular arrangement

2. Physiology

   • Somatic motor unit (1)
     • motor neuron and all the muscle fibres it supplies
       • Acetylcholine released
         • Na+ channel opens
           • Depolarization
     • Excitation-contraction coupling(1)
       • Sliding Filament Model(1)
         • Formation of cross bridges between myosin head & actin
           • Cross bridges form & break for several times
             • Tension propels thin filaments toward the centre of the sacromere
               • Muscle cell contracts (Z discs & I bands shorten)
         • Contractions(1)
           • Twitch
             • Isotonic
               • Isometric
                 • Tetanic
                   • frequent stimulations at maximum tension and no relaxation period
                 • no change in length
               • change in muscle length
                 • Concentric - shorten
                 • Eccentric - lenghten
             • rapid & brief contraction due to one action potential
       • Action potential starts in propagates
         • AP travels trough sarcolemma and T Tubules
           • Ca2+ is released and binds to troponin, allowing myosin to bind to actin

3. Pathology

   • Muscle dystrophy
     • Group of genetic conditions causing progressive muscle weakness and atrophy
       • Caused by mutations of the dystrophin protein complex in sarcolemma
         • Lack of dystrophin leads to membrane destabilization & changes handling of intracellular Ca2+
     • Symptoms(5)
       • -trouble walking & standing -loss of reflexes -swallowing & breathing problems -lung & heart weakness
     • Diagnostic(3)
       • Blood test for the genetic markers of MD
       • Muscle biopsy
       • electromyography test
     • Treatment(4)
       • no cure, only ways to slow down
         • physiotherapy
           • maintains muscle strength & flexibility
         • corticosteroid medication
           • improves muscle strength for 6 months - 2 years
         • creatine supplements
           • supplies muscle and nerve cells with energy

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