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10 Cards in this Set
- Front
- Back
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Muscle Metabolism: Energy for Contraction
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• ATP is the only source used directly forcontractile activities
• During maximal physical activity, availablestores of ATP are depleted in 4–6 seconds • ATP is regenerated by: 1. Direct phosphorylation of ADP by creatine phosphate (CP) 2. Anaerobic pathway (glycolysis) 3. Aerobic respiration |
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Anaerobic Pathway
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• Oxygen delivery is impaired
• Pyruvic acid is converted into lactic acid • Lactic acid: • Diffuses into the bloodstream • Used as fuel by the liver, kidneys, and heart • Converted back into pyruvic acid by the liver |
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Aerobic Pathway
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• Produces 95% of ATP during rest and lightto moderate exercise
• Fuels: stored glycogen, then bloodborneglucose, pyruvic acid from glycolysis, andfree fatty acids |
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Smooth Muscle
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• Found in walls of most hollow organs(except heart)
• Usually in two layers (longitudinal andcircular) -Spindle-shaped fibers: thin and shortcompared with skeletal muscle fibers - Connective tissue: endomysium only - SR: less developed than in skeletal muscle -Pouchlike infoldings (caveolae) ofsarcolemma sequester Ca2+ - No sarcomeres, myofibrils, or T tubulesCopyright © 2010 Pearson Education, Inc. |
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Peristalsis
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• Alternating contractions and relaxations ofsmooth muscle layers that mix andsqueeze substances through the lumen ofhollow organs
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Innervation of Smooth Muscle
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• Autonomic nerve fibers innervate smoothmuscle at diffuse junctions
• Varicosities (bulbous swellings) of nervefibers store and release neurotransmitters |
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Contraction of Smooth Muscle
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-Slow, synchronized contractions
-Cells are electrically coupled by gap junctions -Some cells are self-excitatory (depolarizewithout external stimuli); act aspacemakers for sheets of muscle -Rate and intensity of contraction may bemodified by neural and chemical stimuli • Sliding filament mechanism • Final trigger is intracellular Ca2+ • Ca2+ is obtained from the SR andextracellular space |
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Role of Calcium Ions
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-Ca2+ binds to and activates calmodulin
- Activated calmodulin activates myosin (light chain) kinase - Activated kinase phosphorylates andactivates myosin - Cross bridges interact with actin |
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Muscular Dystrophy
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• Group of inherited muscle-destroyingdiseases • Muscles enlarge due to fat and connectivetissue deposits
• Muscle fibers atrophy |
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Duchenne Muscular Dystrophy (DMD)
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• Most common and severe type
• Inherited, sex-linked, carried by females andexpressed in males (1/3500) as lack of dystrophin (a very large protein involved in stabilizing theactin-myosin filment structure of striated muscle) • Victims become clumsy and fall frequently; usuallydie of respiratory failure in their 20s • No cure, but viral gene therapy or infusion of stemcells with correct dystrophin genes show promise |
