Exercise Physiology Test 3 I Structural Aspects of Skeletal Muscle a Know what general proteins that comprise the thick and thin filaments i Thick Filament Proteins 1 Myosin 2 C Protein structural protein that holds the myosin tails in a correct contractile protein that splits ATP and is responsible for the power stroke of the myosin head spatial arrangement may hold H protein of an adjacent thick filament at an even distance during force generation may also control the number of myosin molecules in a thick filament myosin heads part of the M line helps hold the thick filament in place part of M line provides strong anchoring point for the protein Titin provides ATP from phosphocreatine located proximal to the 3 M protein 4 Myomesin 5 M CK 6 actin attaches actin filaments together at the Z disk 7 Desmin vimentin synemin link Z disks of adjacent myofibrils have structural and functional roles as together sarcolemma proteins 8 Spectral and dystrophin 9 Titin Helps keep the thick filament centered between the two Z lines during contraction by linking them ii Thin Filament Proteins 1 Actin 2 Tropomyosin main contractile protein interacting with myosin during excitation contraction coupling Regulatory rope like protein that extends over the entire length of F actin Under resting conditions it blocks the myosin binding sites on actin 3 Troponin subunits Found in every 7th G actin along the thin filament Three 1 TnI inhibitory subunit inhibits movement of tropomyosin by positioning tropomyosin on the actin binding site 2 TnT tropomyosin binding subunit binds loosely onto tropomyosin to prevent it from moving off of actin 3 TnC calcium binding subunit contains four binding sites for calcium two of them have high affinity and at rest Mg2 binds to them Two of the binding sites have low affinity for Ca2 and they are empty at rest Cardiac muscle only has 3 total ions Activation when the intracellular calcium level rises to a critical level four calcium ions bind to the TnC thereby causing the entire subunit configuration to change TnT then binds tightly to tropomyosin and the entire troponin protein physically moves tropomyosin to expose the myosin binding sites on actin Once the myosin binding site is exposed S 1 sub fragment of myosin can insert creating cross bridge b Know what the sarcolemma and sarcoplasm are i The sarcolemma surrounds the muscle fiber beneath the endomysium and encloses the fiber s cellular contents It is comprised of both the plasma and basement membranes 1 The basement membrane is the outermost covering collection of 2 glycoproteins and collagen network that is freely permeable to proteins solutes and other metabolites The plasma membrane is the true cell boundary that is found just beneath the basement membrane The plasma membrane is made up of a lipid bilayer and is much more selective to ions solutes and substrates Functions Maintains the proper acid base balance allowing it to contract repeatedly during exercise Involved in propagating an action potential that will lead to muscle contraction conducts wave of depolarization over each muscle fiber Transports metabolites from the blood in the capillaries to the center cytosol of the muscle fiber Serves as an elaborate region of functional folds at the neuromuscular junction Contains caveolae which provide additional length during fiber stretching allows lengthening to occur without damaging the plasma membrane Insulates the fibers ii The sarcoplasm interior of the plasma membrane rich in soluble proteins myofilaments and true myonuclei as well as high energy intermediates ATP PC substrates glycogen and lipids enzymes of metabolism mitochondrial proteins ribosomes for protein synthesis cytosolic proteins and so on c Know what the t tubules and sarcoplasmic reticulum are ii T Tubule system i Sarcoplasmic reticulum network of tubular channels and vesicles that provide the structural integrity to the cell Allows for the depolarization waves to spread rapidly from outer cell to inner cell Stores calcium ions depolarization waves contains pumps that take up calcium from the fiber s sarcoplasm creating a calcium gradient between the SR higher and the sarcoplasm surrounding the filaments lower found within the SR provides for the spreading of d What is a sarcomere and what are its boundaries A sarcomere is the strongest contractile unit of a skeletal myofiber The sarcomere length is the distance from one Z disk to the next optimal length 2 5 m The optimal length is directly proportional to the capacity for force generation doesn t have high force capacity if it s too small or too large length tension relationship A band dark band I band isotropic band H zone central region of the A band where there is no thick and thin filament overlap H zone is bisected by the M line M line composed of proteins that keep the sarcomere in proper spatial orientation as it lengthens and shortens Z disks most dense e Functional importance of muscle fiber to muscle length ratio The ratio of different muscle type fibers will dictate the function of the muscle Long muscle fibers will produce a higher active muscle range because there are more sarcomeres in series it would have the same peak force as a short muscle fiber Additionally fiber length increases the muscle s absolute maximum contractile velocity and a longer range before muscle action is depleted Shorter fiber to muscle ratios correlate to muscles used for contractile force Longer fiber to muscle ratios correlate to muscles used for speed i Ex Medial gastrocnemius calf vs Sartorius muscle hamstring vs eye 1 Medial Gastronemius length of about 250mm with fiber lengths of 35mm 15 of muscle length The muscle fiber makes up a small percent of the muscle and it correlates to a high force capacity This is why calf muscles are used in exercises like jumping 2 Sartorius Muscle length of about 500 mm with fiber lengths of 450mm 90 of muscle length Increased muscle fiber length in long muscles correlates to increased velocity Intraocular muscles of eye 1 2mm fine movements that don t require a lot of force 3 f How do endurance and resistance training affect the size of a muscle fiber and why is the this case in terms of diffusion of oxygen and other nutrients to the center of the muscle i Endurance 1 Slow Twitch fiber size will either remain the same or increase which will allow for a significantly higher oxidative capacity either way Higher oxidative capacity will allow more oxygen to be
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