PHYSIOLOGY OF EXERCISE – PET 3380 REVIEW GUIDE FOR EXAM 3 Structural Aspects of Skeletal Muscle 1. Know what general proteins that comprise the thick and thin filaments. a. Thick Filaments: i. Myosin – Splits ATP and is responsible for the “power stroke” of the myosin head ii. C protein – holds myosin thick filaments in a regular array & controls # of myosin molecules in a thick filament iii. M protein – helps hold thick filaments in a regular array iv. Myomesin – provides a strong anchoring point for the protein titin v. M-CK – provides ATP from phosphocreatine; located proximal to the myosin heads b. Thin Filaments: i. Actin – interacts with myosin during excitation-contraction coupling ii. Tropomyosin – transduces the conformational change of the troponin complex to actin iii. Troponin – Binds Ca2+ and affects tropomyosin; signal that induces crossbridge cycling iv. Nebulikn – control the number of actin monomers joined to each other in thin filament 2. Know what the sarcolemma and sarcoplasm are a. Sarcolemma – thin, elastic membrane that encloses the fiber’s cellular contents i. Plasma membrane - conducts electrochemical wave of depolarization over muscle fiber surface 1. Caveolae – allows for lengthening of plasma membrane 2. More selective to ions, solutes and substrates crossing it, and critical for cell function ii. Basement membrane: fuses with tendon bone iii. Satellite Cells – between Plasma and Basement membrane; myogenic stem cells b. Sarcoplasm – cytoplasm; contains proteins, minerals fats, organelles, glycogen and myoglobin 3. Know what the t-tubules and sarcoplasmic reticulum are a. Transverse Tubules (T-tubules) – Transport system deep into fiber, allows rapid conduction of impulse b. Sarcoplasmic Reticulum (SR) – membranous channel parallel to myofibril and storage site for calcium 4. What is a sarcomere and what are its boundaries? a. Sarcomere - smallest contractile unit of skeletal muscle fiber i. Boundaries: Z disc to Z disc5. Functional importance of muscle fiber to muscle length ratio a. Muscle Fiber to Muscle Length Ratio – varies between 0.2 and 0.6 b. Short Muscle Fiber and Short Muscle Length produces more force and velocity (low ratio) i. Quadriceps and plantar flexors c. Long Muscle Fiber and Long Muscle Length produces less force and velocity (high ratio) i. Hamstrings and dorsiflexor 6. 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? a. 7. 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. a. Fast-Twitch Fibers: i. High capability for electrochemical transmission of action potentials ii. High myosin ATPase activity iii. Rapid CA2 release and uptake by an efficient sarcoplasmic reticulum iv. High rate of crossbridge turnover v. Sports: “Stop and Go” – basketball, soccer, lacrosse or field hockey vi. Large cross sectional area vii. Quick to fatigue viii. Muscle Type: 1. IIA – fast shortening speed and moderately well-developed capacity for energy transfer from both aerobic and anaerobic sources 2. IIX – paid shortening velocity (true fast twitch fibers) b. Slow-Twitch Fibers: i. Low myosin ATPase activity ii. Slow calcium handling ability and shortening speed iii. Less well-developed glycolytic capacity than fast-twitch fibers iv. Large and numerous mitochondria, higher capillary density v. Sports: endurance sports vi. Smaller cross sectional area vii. Fatigue resistant viii. Muscle Type: 1. I – slow twitch fibers 8. Know any exercise-induced adaptations a. Type of exercises helps shift fiber type slightly to type of training i. Explosive/power training – builds more fast twitch fibers ii. Aerobic Training – builds more slow twitch fibersMuscular Contraction 1. What mineral is the key to muscular contraction? a. Calcium (Ca2+) – binds to troponin complex to open up the Actin active site 2. Know the role of troponin and tropomyosin in muscular contraction a. Troponin – a complex of three regulatory proteins (troponin C, troponin I and troponin T) that is integral to muscle contraction i. Contains binding site for calcium to open up the Actin active site b. Tropomyosin – protein attached to troponin that blocks the actin active site 3. 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. a. Sliding-Filament Theory – muscle shortens or lengthens because the thick and thin filaments slide past each other without changing length. The myosin crossbridges attach, rotate and detach from the actin filaments with energy from ATP hydrolysis to drive fiber shortening. i. Controversy – multiple cross-bridge cycles occur foe each ATP hydrolyzed b. Hypothetical scheme of cross-bridge cycle: i. Step 1 – Ca2+ is released from the SR and the myosin head attaches to actin ii. Step 2 – Tension is developed and movement occurs with the release of ADP and Pi iii. Step 3 – Actin and myosin dissociates in the presence of ATP iv. Step 4 – ATP is hydrolyzed and Myosin is energized and return to resting state. c. “working stroke” – cross-bridge moves an actin filament through 10nm in the space of 2ms while hydrolyzing 1 ATP molecule 4. Principles, theories, and relationships: e.g. size principle, length-tension relationship and etc. a. Length-tension – Optimum Length (2.05-2.2uM) i. Greatest overlap that allows for the highest active tension ii. Too long, there is no myosin/actin overlap or tension iii. Too Short – sarcomere interfere with each other b. Force – Velocity – inversely related i. More Force, less velocity ii. More Velocity, less force5. 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 a. Excitation-Contraction – physiological process of converting an electrical stimulus to
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