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PHYSIOLOGY OF EXERCISE – PET 3380- REVIEW GUIDE FOR EXAM 3 - Structural Aspects of Skeletal Muscle o 660 skeletal muscles; muscles constitute approx. 45% body weighto Major site of energy transduction and storageo 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 capillarizationo 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 alterationso Increase= hypertrophyo Decrease= atrophy- Activity-determined phenotype (e.g. I, IIa, IIx)o Myofiber proteins: Contractile proteins: - myosin and actin Regulatory proteins:- tropomyosin and troponin (together produce muscle contraction) Structural proteins: - 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 contentso Sarcoplasm- Cytoplasm: contains proteins, minerals, fats, organelles, glycogen, myoglobino 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: An additional elastic membrane found just beneath the basement membrane= true cell boundary At a muscle fiber’s resting length, the plasma membrane has the morphologicalcharacteristic 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 bando Represents the lighter area (Isotrophic band) - A bando Represents the darker area- Z lineo 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 casein 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 fiberso 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 capacityfor 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- HIGHo 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


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FSU PET 3380C - REVIEW GUIDE FOR EXAM 3

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