Chapter 6 Contraction of Skeletal Muscle Dr. Marko Ljubković Department of Physiology

Anatomy of Skeletal Muscle Muscle fibers Myofibrils Sarcomeres

Sarcomere Myofibrils SR Anatomy of Skeletal Muscle

Actin and Myosin Filaments

Cross-bridge Cycle

Muscle Length-Force Relationship

Velocity-Load Relationship Determined by isotonic contraction

Sources of Energy for Contraction 1.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

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 fibers 3.Both types found in individual muscle

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)

Muscle Growth