Excitation, Contraction, And Relaxation Of Muscular System

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Excitation, Contraction, and Relaxation of Muscular System

Skeletal Muscle contraction requires a great deal of energy. Energy is required to break the bond between the myosin head and the actin active sites as well as for removal of calcium from the cytoplasm by the use of a special pump within the sarcoplasmic reticulum. When the myosin head is tilted forward, after the power stroke, a binding site for ATP (the chief energy currency of the cell) is exposed. The breakdown of ATP to ADP releases the head from the actin filament and cocks it for the next ratchet power stroke

Energy is required for muscle contraction. At rest and during light exercise, muscles use lipids as their energy source. The use of carbohydrate becomes more important as the intensity of exercise increases. The breakdown of glucose to water and carbon dioxide generates energy that is transferred to regenerate phosphorylcreatine and ATP. When oxygen supplies are inadequate this process is short circuited and a metabolite (lactic acid) of one of the products builds up in the muscle. This is called anaerobic metabolism (glycolysis) and is a normal process that can occur prior to the oxidative breakdown of glucose. The lactate builds up in the muscles causing a change in pH that inhibits enzyme activity. After the exercise, an oxygen debt exists in that oxygen must be used to convert the lactate into carbon dioxide and water and replenish energy stores. Short intense exercise utilizes anaerobic metabolic mechanisms more than more sustained activities. For example, in a 100 m dash 85% of the energy is derived from anaerobic means while in a mile run only 20% is generated anaerobically.

Excitation-Contraction Coupling
Contraction in skeletal muscle begins with an action potential in the muscle fiber. This causes the release of calcium from the sacroplasmic reticulum. The action potential in the muscle fiber begins after it is excited by interaction with a large ...