A&P

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List, Describe and Compare the excitation, contraction and relaxation of the skeletal, cardiac and smooth muscles.

Skeletal Muscle
Skeletal Muscle contraction requires a massive deal of energy. This 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. Once the myosin head is tilted forward, after the stroke, a binding site for ATP is exposed. The breakdown of ATP to ADP releases the head from the actin filament and gets it ready for the next stroke. Energy is required for muscle contraction.

At rest and during light exercise, muscles use lipids as their energy source this is the relaxation process. 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 of one of the products builds up in the muscle. This is called anaerobic metabolism and is a normal process that can occur prior to the oxidative breakdown of glucose.

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 insulated (myelinated) nerve fiber. The point of contact of the nerve and muscle is called the neuromuscular junction which is normally located in the middle of the muscle fiber. Therefore an action potential initiated here spreads toward the ends of the fiber making it possible for all sarcomeres to contract at the same time. Skeletal muscle has an adaptation that allows the action potential to spread deep within the fiber. The T or transverse tubules are internal extensions...