Structural Aspects of Skeletal Muscle Know what general proteins that comprise the thick and thin filaments o Thick o Thin Myosin Actin filaments tropomyosin troponin complex Know what the sarcolemma and sarcoplasm are o Sarcolemma o Sarcoplasm Plasma membrane basement membrane Fuses with tendon bone Cytoplasm Contains proteins minerals fats organelles glycogen myoglobin Know what the t tubules and sarcoplasmic reticulum are o Transverse tubules Infoldings of sarcolemma that conduct electrical impulses from surface of cell to deep within cell Allows rapid conduction of impulses o Sarcoplasmic reticulum Smooth endoplasmic reticulum surrounding each myofibril Membranous channel parallel to myofibril Storage site for calcium Ca2 What is a sarcomere and what are its boundaries o Sarcomere Smallest contractile unit of skeletal myofiber Functional importance of muscle fiber to muscle length ratio o Fiber Length Muscle Length Ratio Long muscle fibers high velocity low force output Short muscle fibers low velocity high force output 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 o Endurance Relatively normal sized muscle fibers However tendency for enlargement of slow twitch fibers Have mostly slow twitch fibers which possess more mitochondria than fast twitch meaning greater O2 diffusion Slow twitch receive the largest quantity of blood which means more nutrients o Resistance Definite enlargement of both fiber types particularly fast twitch Enlargement of muscle s contractile apparatus Lower O2 diffusion because less mitochondria less need to diffuse O2 Utilize Creatine Phosphate which regenerates rather quickly and doesn t need many nutrients 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 Type I Myosin ATPase activity Low Shortening velocity slow Mitochondrial density high Capillary density high Cross sectional area small Rate of fatigue can last for hours Sports Distance runners cross country skiers o Type IIA o TYPE IIX Myosin ATPase activity high Shortening velocity moderately fast Mitochondrial density high Capillary density intermediate Cross sectional area high Rate of fatigue about 30 mins Sports weightlifting sprinters Myosin ATPase activity high Shortening velocity fast Mitochondrial density medium Capillary density low Cross sectional area high Rate of fatigue about 5 mins Sports Basketball soccer lacrosse Know any exercise induced adaptations o Endurance athletes possess predominately slow twitch muscle fibers o Power athletes and elite sprint athletes possess mainly fast twitch muscle fibers Muscular Contraction What mineral is the key to muscular contraction o Ca2 is the key mineral to muscular contraction Calcium interacts with the troponin complex to move the tropomyosin away from binding sites on actin filaments Creates a binding site for the myosin cross bridges to attach to the actin filaments Know the role of troponin and tropomyosin in muscular contraction o Tromomyosin Distributes along the length of the actin filament in a groove formed by the double helix Inhibits actin and myosin interaction when covering myosin binding sites o Troponin Three subunit protein complex that are embedded at fairly regular intervals along actin strands Exhibit a high affinity attraction for Ca2 Ca2 causes a conformational change in troponin causing it to move tropomyosin During muscle contraction when troponin complexes are stimulated by Ca2 they move tropomyosin strands away from myosin binding sites and allow muscle contraction to proceed 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 1 Myosin crossbridge attaches to the actin myofilament 2 The myosin head pivots and bends as it pulls on the actin filament sliding it toward the M line Working Stroke 3 As new ATP attaches to the myosin head the crossbridge detaches 4 As ATP is split int ADP and Pi cocking of the myosin head occurs Principles theories and relationships e g size principle length tension relationship and etc o Size principle Upon stimulation smaller Type I motor units contract first followed by larger Type IIa and larger Type IIx motor units as neuronal stimulation intensifies o Length tension relationship Tension developed is proportional to the degree of overlap between the actin and myosin filaments Optimum length is 2 05 2 2 micrometers No tension between actin and myosin when fibers are stretched past 3 75 micrometers When the sarcomere if fully contracted the developed o All or None principle force is 0 unit contract fully With the activation of a motor unit all of the muscle fibers in the Know Excitation Contraction EC coupling Be able to describe the sequences involved in EC Coupling muscle contraction from release of ACH from the motor neuron all the way until relaxation o See page 370 in textbook for detailed diagram 1 Generation of action potential in motor neuron causes vesicles within the terminal axon to release ACh acetylcholine ACh diffuses across synaptic cleft and attaches to specialized ACh receptors on sarcolemma 2 Muscle action potential depolarizes the transverse tubules T tubule at the the sarcomere s A I junction 3 Depolarization of T tubule system causes Ca2 release from sarcoplasmic reticulum s lateral sacs 4 Ca2 binds to troponin in the actin filaments a This releases the inhibition that prevented actin from combining with myosin 5 During muscle action actin combines with myosin ATPase to split ATP and cause energy release Tension created from the energy release produces myosin crossbridge movement 6 ATP bind to myosin crossbridge breaking the actin myosin bond allowing the crossbridge to dissociate from actin This leads to sliding of thick and thin filaments causing muscle shortening a This is where the Sliding Filament Hypothesis is derived from 7 Crossbridge activation continues when the concentration of Ca2 remains high from depolarization to inhibit action of the troponin tropomyosin complex 8 When muscle stimulation ceases Ca2 moves back
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