The Musculoskeletal System

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The musculoskeletal system has many functions to it because it is actually two systems that are put together; muscular and skeletal. The organs that are in these systems are skeletal muscles, bones (joints, tendons, and ligaments). By dividing the two systems into different sections, it will make it easier for you, the reader, to understand and make sense of the information.

The muscular system functions are to provide movement, protects organs, and production of heat. There are many muscles that do different functions. Before I go into all of the muscular functions, I will give an overview of all the muscle structure. Fascia, which is a fibrous connective tissue, separates an individual skeletal muscle from adjacent muscles and then holds it into position. Fascia surrounds each muscle and protects beyond the end of its muscle fibers to form a tendon. The aponeuroses tissues are the forms broad fibrous sheets that attach to the coverings of adjacent muscles. The epimysium lies beneath the fascia, the perimysium extends into the structure of the muscle, where muscle cells separate into fascicles. Endomysium separates individual muscles fibers. Skeletal muscle fibers contract in response to stimulation and then relax when the stimulation ends. Threadlike structures called myofibrils run lengthwise throughout the muscle fiber. The myofibrils are composed of two types of even tinier structure, the myofilaments. The thick myofilaments called myosin filaments consist mainly of the protein myosin. The actin filaments consist of the protein actin. Myosin and actin filaments are arranged lengthwise in the muscle fibers so that they overlap.

During muscle contaction, the actin filaments are pulled inward between the myosin filaments. As that occurs; a nerve cell that stimulates a muscle releases a compound known as acetylcholine. The acetylcholine goes across the muscle-nerve and combines with receptors on the surface of the muscle cell. Then the electrical current spreads over the sarcolemma (cell membrane). Excess acetylcholine is broken down by the enzyme cholinesterase. The electrical current spreads and stimulates the sarcoplasmic reticulum (endoplasmic reticulum) to release calcium ions. The calcium then processes the uncovers binding sites on the actin filaments. This process is powered by the energy from adenosine triphosphate (ATP) molecules. As this process continues, the actin filaments slide past the myosin filaments, shortening the muscle.

Muscle cells are needed to provide us with large amounts of energy. Sufficient ATP can be piled to store energy for only the first few seconds of activity. Creatine phosphate is muscle cells that have another energy storage compound. The supply of creatine phosphate does not last long during exercise. Stored glycogen is degraded while yielding glucose. When sufficient oxygen is available enough, energy is captures from the glucose to produce needed quantities of ATP. Oxygen many not always be available to meet the needs of rapid metabolizing muscle cells. Muscle cells are capable of breaking down fuel molecules without oxygen for short periods of time. Muscle tone is an unconscious process that helps to keep muscles prepared for action. Without knowing it, while you are lifting a heavy object, muscles are shortened and thicken as they contract. If you push against a locker, no movement occurs. Muscle length does not change but muscle tension may increase.

Skeletal muscles produce movements by pulling on tendons. Muscles can only pull, they cannot push. Synergists stabilize joints so that undesirable movement does not occur and fixators stabilize the origin of an agonist (a muscle that contracts to produce a particular action) so that its force is fully directs to the bone on which it inserts. Synergists and fixators are muscles that help the agonists by reducing unnecessary movement.

Heat is a necessary need for human bodies. About twenty-five percent of the energy released...
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