REVIEW GUIDE FOR EXAM 3 PHYSIOLOGY OF EXERCISE PET 3380 Structural Aspects of Skeletal Muscle o 660 skeletal muscles muscles constitute approx 45 body weight o Major site of energy transduction and storage o End organ for the primary support systems involved in exercise such as cardiovascular and pulmonary o Layer of Skeletal Muscle Epimysium outermost layer Perimysium middle layer wraps around the fascicles connective tissue Contain fasiculli major site of blood vessels and nerves Endomysium between fibers innermost layer Endomysium is around muscle fiber cell within a fascicle Contain muscle fibers major site of capillarization o Muscle organ Consists of hundreds to thousands of muscle cells plus connective tissue wrappings blood vessels and nerve fibers covered entirely with epimysium o Fascicle a portion of the muscle Discrete bundle of muscle cells segregated from the rest of the muscle by a connective tissue sheath surround by a perimysium o The Skeletal Myofiber muscle cell Multinucleated peripheral Terminally differentiated Highly plastic Load driven size alterations o Increase hypertrophy o Decrease atrophy Activity determined phenotype e g I IIa IIx o Myofiber proteins Contractile proteins myosin and actin Regulatory proteins Structural proteins tropomyosin and troponin together produce muscle contraction C protein part of the thick filament involved in holding the tails of myosin in a correct spatial arrangement Titin links the end of the thick filament to the Z disk Know what general proteins that comprise the thick and thin filaments o Two types of myofilaments thick filaments composed of bundles of myosin and thin filaments composed of strands of actin o Tropomyosin and troponin are regulatory proteins present in thin filaments Know what the sarcolemma and sarcoplasm are o Sarcolemma Plasma membrane basement membrane fuses with tendon bone A thin elastic membrane that encloses the fiber s cellular contents o Sarcoplasm Cytoplasm contains proteins minerals fats organelles glycogen myoglobin o Cytoplasm Cytosol Interior to the plasma membrane Rich in soluble proteins myofilaments and true myonuclei as well as store high energy intermediates ATP PC substrates glycogen and lipids enzymes of metabolism mitochondrial proteins ribosomes for protein synthesis cytosolic proteins and so on o Plasma Membrane true cell boundary An additional elastic membrane found just beneath the basement membrane At a muscle fiber s resting length the plasma membrane has the morphological characteristic of small indentations termed caveolae provide additional length during fiber stretching Know what the t tubules and sarcoplasmic reticulum are o Transverse Tubules transport system deep into fiber allows rapid conduction of impulse T tubules are infoldings of the sarcolemma that conduct electrical impulses from the surface of the cell to the terminal cisternae T tubules system runs perpendicular to the myofibril o Sarcoplasmic reticulum is a smooth endoplasmic reticulum surrounding each myofibril SR is an extensive longitudinal laticelike network of tubular channels and vesicles SR membranous channel parallel to myofibril and storage site for Calcium Ca2 What is a sarcomere and what are its boundaries o Sarcomere the smallest contractile unit of skeletal myofiber Sarcomere consists of the basic repeating unit between two Z lines This structural entity comprises the functional unit of a muscle fiber Optimal sarcomere length in mammalian muscle 2 4 to 2 5 um Sarcomere has a striated appearance I band A band Z line o Represents the lighter area Isotrophic band o Represents the darker area o Bisects the I band and adheres to the sarcolemma it provides stability to the entire structure most dense Each sarcomere contains 2 triads A triad is the repeating pattern of two vesicles and a T tubule in each Z line region Functional importance of muscle fiber to muscle length ratio o Ratio of individual fiber length to a muscle s total length usually varies between 0 2 and 0 6 This means that individual fibers in the longest muscles such as the upper and lower limbs remain significantly shorter than the muscle s overall length How do endurance and resistance training affect the size of a muscle fiber and why is this case in terms of diffusion of O2 and other nutrients to the center of the muscle Know the differences between muscle fiber types I IIA IIX in terms of myosin ATPase activity shortening velocity mitochondrial and capillary density cross sectional area and in general what sports and activities fast IIA IIX and slow I fibers support Also know general rates of fatigue of each fiber o Muscle Fiber Types Type I slow Low Myosin ATPase activity Slow calcium handling ability and shortening speed Less well developed glycolytic capacity than fast twitch fibers o Glycolytic capacity LOW Capillary Mitochondrial Density HIGH Activity used for Aerobic hours Type IIA fast fatigue resistance Exhibit fast shortening speed and a moderately well developed capacity for energy transfer from both aerobic SDH and anaerobic PFK Contraction time moderately fast High myosin ATPase activity Rapid CA2 release and uptake by an efficient SR Capillary Density INTERMEDIATE mitochondrial HIGH Glycolytic capacity HIGH Activity used for long term anaerobic less than 30 minutes Type IIX fast fatigable Contraction time FAST Activity used for Short term anaerobic less than 5 minutes Mitochondrial Density MEDIUM Capillary Density Intermediate Glycolytic capacity HIGH o On average most people contain 45 55 slow twitch fibers in their limb muscles Know any exercise induced adaptations o Endurance athletes Possess predominantly slow twitch fibers in the major muscles activated in their sport o While weightlifters ice hockey players and sprinters have more fast twitch fibers and relatively lower aerobic capacities Muscular Contraction What mineral is the key to muscular contraction o Intracellular Calicum Know the role of troponin and tropomyosin in muscular contraction o Tropomyosin inhibits actin and myosin interaction tropoinin plus Ca2 trigger the myofibrils to interact and slide past each other Describe the chemical and mechanical steps in the cross bridge cycle and explain how the cross bridge cycle results in shortening of the muscle Sliding Filament Hypothesis and Hypothetical scheme of cross bridge cycle etc o The Sliding Filament Model The theory proposes that a muscle shortens or lengthens because the thick and thin
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