__solution__________________ Name PHYSIOLOGY 42-202 Homework-3 problems 1 October 2008 20 points Homework is due by 5 pm Wednesday 8 October as a typewritten hardcopy ONLY (NO HANDWRITTEN DOCUMENTS PLEASE) Please turn in either in class or drop off in my mailslot at ICES, Hamburg Hall. DIRECTIONS: Answer questions using notes, textbook, or other sources. YOU MUST IDENTIFY and REFERENCE YOUR SOURCES. Provide answers on attached sheets. Please resist the urge to copy paste, please put the answers in your own words AND limit your answers to no more that 2-3 pages. For homework turned in with anything over and points maybe taken away. Reviewing Concepts (2 point) 1. Describe how oxidative muscle fibers differ from glycolytic fibers, and explain how each of these factors relates to the ability of a fiber to resist fatigue. (2 point) 2. Explain the size principle and how it relates to the amount of tension developed by a skeletal muscle. (2 point) 3. Describe the relationship between contractile force and action potential frequency in skeletal muscle. (2 point) 4. Glycolysis under anaerobic conditions provides approximately 5% of the energy that could be produced under aerobic conditions. Thus, one might assume that anaerobic exercises (such as weight training) would be a better way to lose weight than aerobic exercise. Explain why this is not true. (2 point) 5. Describe the sliding filament model of contraction. Critical Thinking and Clinical Applications (2 points) 6. Jim does research on calcium signaling. One day, while in the lab, Jim carelessly
left a syringe full of highly concentrated thapsigargin on a bench, and while working later, accidentally stabbed himself with it. The thapsigargin went directly into a vein. A short time later, Jim was lying on the floor, dead. What organ failed (first)? Describe what probably happened to Jim on a subcellular level.
(2 points) 7. What is the functional reason why the muscle group on the dorsal leg (calf) is so much larger than the muscle group in the ventral region of the leg? (2 points) 8. Julie Jumpsohigh is waiting impatiently for the physician to finish removing the cast from his leg, which she broke the last day of school six weeks ago at the track and field meet. Summer vacation is half over, and she hasn't been able to swim, high jump, or participate in any of her favorite sports. When the cast is finally off, Julie's excitement is replaces with concern when she sees that the injured limb is noticeably smaller in diameter than her normal leg. What is the explanation for this reduction in size? How can the leg be restored to its normal size and functional ability?
(2 points) 9. What type of off-the-snow training would you recommend for a competitive downhill skier versus a competitive cross-country skier? What adaptive skeletal muscle changes would you hope to accomplish in the athletes in each case? (2 points) 10. You're setting around the tellie one night watching CSI (the original one, not the Miami or New York knock-offs) with your mates. One of your mates notes the stiffness in one of the many morgue "subjects." You show your physiological prowess by explaining the process of rigor mortis. So tell me how you described it, in detail please. 1. Oxidative fibers are smaller in diameter, have more myoglobin, less sarcoplasmic reticulum, fewer glycolytic enzymes, more mitochondria, and a greater capillary density than glycolytic fibers. This enables them to be much more resistant to fatigue than glycolytic fibers because they have a greater supply of oxygen (increased capillary) and fuel to the cells, as well as a greater ability to use cellular respiration (more mitochondria) as opposed to glycolysis (fewer glycolytic enzymes) as their primary metabolic pathway. This decrease the amount of lactic acid produced. Lactic acid accumulations associated with development of fatigue by a muscle cell. 2. The size principle is a description of motor unit recruitment in skeletal muscle. It says that the smallest motor units are recruited first, followed by successively larger motor units a more force is required by the muscle as a whole. When maximum force is require, all available motor units are recruited. 3. In skeletal muscle, as action potential frequency increases, successive twitches begin to fuse with each other and contractile force rises. Eventually, when action potentials are delivered in very close succession, fused tetanus occurs and maximum occurs and maximum isometric force is reach3ed (seen as a plateau region in the graph). In contrast, action potentials in cardiac muscle have very long refractory periods. Because of this, tension falls to near zero before another action potential can be received by the muscle cells. This prevents titanic contractions from occurring in cardiac muscle. 4. Although high intensity exercises burn energy faster than low intensity exercises burn energy faster than low intensity exercises, than can only be for sustained a short period of time before they fatigue. In addition, carbohydrates are the only energy source of anaerobic metabolism. Aerobic exercise, on the other hand, can be sustained for a considerably longer period of time before fatigue. During this time, carbohydrates and lipid can be catabolized for energy. 5. Sliding filament model is based on the contraction of sarcomeres within myofibrils via the sliding of actin filaments across myosin filaments thus shortening sarcomeric length. A sarcomere contracts when myosin heads bind to specific sites on actin resulting in the actin filament sliding along the myosin filament toward the M-line or center of the sarcomere. When a sarcomere shortensThe A band represents the myosin filament and does not change in length. The H zone represents the distance between actin filaments within a sarcomere and gets shorter as the actin filaments in the same plane get closer. The I band represents the distance between myosin filaments between two sarcomeres and gets shorter. The Z disc disk/line represents the connection point between actin filaments between sarcomeres and does not change. 6. The first organ to be encountered by any substance entering the body through a vein will be the heart. The thapsigargin will not have been distributed all over the body by the time it enters the heart, so it will still be at high concentration. Thapsigargin blocks the effect of SERCA (Sarco/Endoplasmic Reticulum Ca2+ ATPase). This protein allows the reuptake of calcium into the sarcoplasmic or endoplasmic reticulum. In the
heart, depolarization causes the SR to release Ca2+ and the drop in calcium levels in the SR causes the opening of the SOC (Store Operated Channel) which imports additional calcium from the extracellular space. This calcium causes the exposure of myosin head binding sites on the actin filaments, and muscular contraction occurs. As long as calcium is present, and ATP is available, contraction will continue. By stopping SERCA, calcium will not be taken back up into the SR, and the SOC will remain open (continuing importation of calcium into the cytosol). Despite the continued activity of Na+/Ca2+ channels and PMCA (Plasma Membrane Calcium ATPase), the level of calcium in the cytosol will remain too high to allow the muscle to relax, or allow the cell to repolarize. The cardiac muscle cells will remain in the contracted state, and the heart will cease pumping blood through the body. Jim will die very quickly as a result. Other possibilities for affected organs would be the liver or kidneys, both of which act as "filters" for the blood. Both organs would end up with very high levels of thapsigargin as well, and would have similar problems with calcium signaling (though no contractile issues, of course) and would fail rather quickly as well. Chances are, Jim would be dead from cardiac failure before this 7. The muscle group (triceps surae) on the dorsal leg (calf) is larger because it must lift you up against the pull of gravity. 8. The muscles in the immobilized leg have undergone disuse atrophy. The physician or physical therapist can prescribe regular resistance-type exercises that specifically use the atrophied muscles to help restore them to their normal size. 9. Regular bouts of anaerobic, short-duration, high-intensity resistance training would be recommended for competitive downhill skiing. By promoting hypertrophy of the fast glycolytic fibers, such exercise better adapts the muscles to activities that require intense strength for brief periods, such as a swift, powerful descent downhill. In contrast, regular aerobic exercise would be more beneficial for competitive cross-country skiers. Aerobic exercise induces metabolic changes within the oxidative fibers that enable the muscles to useO2 more efficiently. These changes, which include an increase in mitochondria and capillaries within the oxidative fibers, adapt the muscles to better endure the prolonged activity of cross-country skiing without fatiguing. 10. Rigor mortis is the phenomenon that occurs after death whereby an individual's muscles become fully contracted or "stiff." Once an individual dies, their cells can no longer generate new ATP. Because ATP is required to pump calcium into the sarcoplasmic reticulum (SR), calcium will diffuse into the sarcoplasm and not be returned to the SR. The increased intracellular calcium levels will cause troponin to pull tropomyosin off the myosin binding sites on actin. This will allow crossbridge cycling to occur. The crossbridges will have been "energized" by the splitting of the last intact ATP molecules inside the cell. Each energized crossbridge will undergo one last powerstroke. The resulting force production is what causes the muscles to "stiffen." The crossbridges cannot detach from actin without intact ATP molecules. Because the supply of ATP is depleted, the muscles remain in the contracted state.