A P II EXAM I Muscular System and Review Power point 1 mentioned in class that there will only be only 5 6 questions put extra emphasis on lever systems and sliding filament theory 9 25 1 Define and identify the anatomy of skeletal muscle and explain the sliding filament theory leading to muscle contraction a Gross anatomy i Nerve and blood supply each muscle is served by one nerve an artery and by one or more veins Each skeletal muscle is supplied with a nerve ending that controls its activity different from smooth muscle contractility which can contract in the absence of nerve stimulation 1 Rich blood supply to account for energy and oxygen delivery as well as for metabolic wastes that must be removed to maintain efficient contractility ii Connective tissue sheaths 1 Epimysium overcoat of dense irregular connective tissue 2 Perimysium muscle fibers grouped into fasciles that that surrounds the whole muscle resemble bundles of sticks each fascicle is surrounded by fibrous connective tissue called perimysium muscle fiber 3 Endomysium fine connective tissue surrounding each b Microscopic anatomy of a skeletal muscle fiber i Size 10 100 um large size and multinucleate system ii Organelles iii Sarcomere a Fuses with the tendon bone 1 Sarcolemma plasma membrane basement membrane 2 Sarcoplasm cytoplasm of a muscle cell containing myoglobin which transports oxygen in the blood contains myofibrils sarcoplasmic reticulum and T tubules 3 Myofibrils rodlike fibers 1 2um 1 A bands dark and I bands light giving striated 2 H zone midsection that shortens during contraction 3 Myofibrils made up of myofilaments account for roughly 80 of cellular volume contain the contractile elements of the muscle cell appearance 4 Contractile filaments a Actin thin filaments i Contains myosin binding sites covered by troponin and tropomyosin b Myosin thick filaments i Two globular heads associated with the light chains business end containing ATP binding sites and ATPase enzymes that split ATP to generate energy for muscle contraction 1 Exists as a multigene family encoding MHC isoforms 2 Isoforms have slight variations in their amino acid composition particularly in S 1 region where energy transduction processes occur 3 Type I SS 0 20 4 Type IIa SS 21 40 5 Type IIx SS 41 60 6 Type IIb SS 61 81 ii Tail containing two heavy chains 5 Regulatory filaments a Tropomyosin rod shaped protein arranged along the actin filaments blocking myosin binding sites on actin so that myosin heads on the thick filaments cannot bind to the thin filaments b Troponin i Troponin I inhibitory subunit that binds to ii Troponin T binds to tropomyosin and helps iii Troponin C binds calcium ions actin position it on actin 6 Structural filaments a Titin elastic protein holding thick filaments in place and helping the muscle spring back into shape after being stretched b C protein part of thick filament holding the tails of myosin in arrangement 7 Sarcoplasmic reticulum elaborate smooth ER with connecting tubules surrounding each myofibril a Regulates intracellular levels of ionic calcium It stores calcium and releases it on demand when the muscle fiber is stimulated to contract gives the final go signal 8 T tubules sarcolemma protrudes deep into the cell interior forming an elongated tube the T tubule a Analogous to the function of villi in the intestines increase surface area b Conduct impulses into the deepest regions of the muscle cell and to every sarcomere signaling the release of calcium c Ensures every myofibril contracts at the same time c Sliding filament model of contraction how muscles contract i Steps 1 Neural stimulus produces an action potential that travels into the muscle membrane From here it travels down to the t tubule where it reaches voltage gate receptors triads 1 t tubule and 2 SRs next to it 2 Action potential reaches the sarcoplasmic reticulum calcium storage receptor RyR which initiates the leave of calcium into muscle cell cytosol 3 Calcium then binds to troponin C which stimulates the a Inhibits troponin I allowing troponin T to bind to conformational change of all three subunits tropomyosin moving the complex out of the myosin binding site b Myosin is already energized as it contains ATP pocket broken down into ADP and Pi and ATPase 4 As myosin binding occurs on the actin filament activation of myosin s cross bridges the force generating sites occurs a Myosin releases ADP and Pi allowing it to change conformation and bind to actin contraction 5 Relaxation must be coupled with contraction so ATP binds to myosin which allows for it to move back to its relaxed state a Calcium has to pump back into the sarcoplasm so that the muscle can relax and continue this contraction relaxation cycle ADP Pi b Myosin is energized again at the end of the cycle ii During contraction the thin filaments slide past the thick filaments so that the actin and myosin filaments overlap to a greater degree 1 In a relaxed state the thick and thin filaments overlap only at the ends of the A band iii The cross bridge attachments act like ratchets to propel the thin iv This collective movement throughout the sarcomere allows for filaments towards the center of the sarcomere the muscle cell to shorten 1 H zone disappears 2 I bands shorten 3 Distance between Z discs is reduced 2 Define and distinguish between the types of muscle fibers and explain the possibilities or lack thereof of fiber type morphology a Type I MHC I MHC I 1 Fibers per motor unit 10 180 2 Motor neuron size small 3 Recruitability easy 1st 4 ATPase activity low 5 Contraction speed slow 6 Relative force production low 7 Number of mitochondria high 8 Resistance to fatigue high 9 Efficiency high 10 Predominant energy system aerobic ii Myosin ATPase is the slowest in these fibers which causes the shortening velocity to be slower as well This basically means Type I fibers contract slowly Mitochondrial and capillary densities are very high in these fibers which allow them to have b Type IIA MHC IIa MHC IIa high oxidative capacity Cross sectional area is small so its contractile force is small iii The oxidative capacity of Type I fibers allows oxygen to be readily available to the muscle cells which makes them ideal for long term aerobic endurance activities Their high oxidative capacity also makes them very fatigue resistant which accounts for why marathon runners can run so long 1 Fibers per motor unit 300 800 2 Motor neuron size large 3 Recruitability moderate 2nd 4 ATPase
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