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Chapter 6
Contraction of Skeletal Muscle
Dr. Marko LjubkovićDepartment of Physiology
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Anatomy of Skeletal Muscle
• Muscle fibers
• Myofibrils
• Sarcomeres
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Sarcomere
Myofibrils
SR
Anatomy of Skeletal Muscle
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Actin and Myosin Filaments
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Cross-bridge Cycle
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Muscle Length-Force Relationship
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Velocity-Load Relationship
Determined by isotonic contraction
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Sources of Energy for Contraction1. ATP pool
2. Creatine phosphate
3. Carbohydrates
• Glycolysis
• Oxidative phosphorylation
4. Fatty acids
• β-oxidation
Oxygen debt• Strenuous ex. (mostly fast
motor units)• Endurance ex. (slow units)
Fatigue• Accumulation of lactic acid
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Types of Muscle Fibers
1. Fast twitch fibers• Thicker muscle fibers and nerves• Extensive SR• Abundance of glycolitic enzymes• Lower mitochondrial content• Different myosin isoform
2. Slow twitch fibers3. Both types found in individual muscle
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Mechanics of Muscle Contraction
1. Motor unit
• α-motor neuron + muscle fibers
• Small (100 to 500 fibers, slow twitch) and Large (1000 to 2000 fibers, fast twitch)
2. Recruitment
• Slow twitch units recruited first
• Spatial summation
• Temporal summation (frequency depends on muscle type)
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Muscle Growth