Physiology

Physiology

1. Structure and function of exercising muscle

   • Skeletal muscle
     • Structural adaptations in skeletal muscle
       • Happen withing 6 weeks of concentric and eccentric training
       • Eccentric training: ↑ muscle fascicle length; ↓ pennation* angle (i.e. the fascicles align better with the direction of the muscle
       • Concentric training: ↓ muscle fascicle length; ↑ pennation angle (i.e. fascicles angled more away from the full muscle’s direction)
       • 4 weeks detraining: o Eccentric training induced adaptations are reversed. oConcentric adaptations are maintained.
       • Thus, structural adaptations to strength training is highly specific to the mode of training.
       • Has effect on injury prevention and development of rehabilitation programs
     • Function of skeletal muscle
       • Force production for locomotion and breathing
       • Force production for postural support
       • Heat production during cold stress
     • Anatomy of skeletal muscle
       • Entire muscle surrounded by epimysium and consists of many bundles (Fasciculi)
       • Fasciculi surrounded by perimysium and consists of individual muscle cell (muscle fiber)
       • Each muscle fiber is a muscle cell with multiple nuclei, surrounded by endomysium, consists of myofibrils divided into sarcomers
         • Structure of muscle fiber
           • Plasmalemma (cell membrane) fuses with tendon, conducts AP from motor neuron to muscle fiber, maintains pH, transports nutrients into muscle fiber
           • Sarcolemma consists of plasmalemma and the basement membrane
           • Satellite cells are between the plasmalemma and the basement membrane, there for muscle growth and development, assists with injury, immobilization, training.
           • Sarcoplasm is cytoplasm of muscle cell, glycogen storage, myoglobin
           • Transverse tubules are extensions of plasmalemma, carry action potential and other substances deep into muscle fiber, waste products out of cell.
           • Sarcoplasmic Reticulum (SR) is longitudinal network of tubules and Ca2+ storage
           • Sarcomeres
             • • Skeletal muscle – striated muscle o A-bands: dark stripes o I-bands: light stripes o H-zone: middle of A-band o M-line: middle of H-zone • Common boundary structure: Z-disk
             • Used for muscle contraction. Made up of actin and myosin
               • Myosin two intertwined filaments with myosin heads. Myosin heads composed of compactly folded polypeptide chains. Stabilized by titin
                 • Titin is a regulatory protein. Located in space between two filaments, attached at various points to the myosin and runs all the way to the Z-disk. Acts as spring mechanism that keeps myosin filaments centred.
               • Actin composed of actin, tropomyosin and troponin. Anchored at Z-disk.

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