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TYPES OF MUSCLE. SKELETAL MUSCLE. Skeletal Muscle. They are used in locomotion and all other voluntary movement. They are fastened to the bones of the skeleton.
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TYPESOF MUSCLE SKELETAL MUSCLE
Skeletal Muscle • They are used in locomotion and all other voluntary movement. • They are fastened to the bones of the skeleton. • It is not made up of clearly defined, seperate cells. Instead, during development, cells fuse together forming individual muscle fibers. • A skeletal muscle is made up of bundles of muscle fibers bound together by connective tissue.
@ Muscle fiber show alternating bands of light and dark. Each fiber is actually a bundle of smaller and smaller fibers called myofibrils. Each myofibril is madeup of still finer protein filaments one thick and one thin. myosin actin
The actin and myosin filaments are arranged in an overlapping pattern that makes the whole muscle fiber looked striped
SLIDING FILAMENT THEORY @ According to the sliding filament theory of muscle contraction the muscle fibers shortenwhen the actin slides over the myosin. As the overlap increases, the fibers shorten.
In the sliding filament model of muscle contraction, the (thin) actin myofilaments [red] (attached to the Z-line) slide (actually, are pulled) inward along the (thick) myosin myofilaments [blue], and the sarcomere (measured from one Z line to the next) is shortened. Note on the measuring scale that as contraction is occuring, both the sarcomere length and the I band (area where thin filaments do not overlap with thick filaments) length decrease, but the A band (area containing thick filaments) length remains constant.
The actin and myosin filaments are arranged in an overlapping pattern that makes the whole muscle fiber looked striped
Crossbridges between actin and myosin filaments allow the fibers to exert a pull. Energy for the sliding of the filaments is supplied by ATP
DURING CONTRACTION • Length of A band does not change • I bands get shorter • H bands disappear • Myosin filaments get closer to the I and Z bands, so length of the muscle fibers shorten • Cross bridges between actin and myosin causes the sliding
VOLUNTARY MOVEMENT • All voluntary movement is started and coordinated by impulse from the brain and spinal cord. • Skeletal muscles are fastened to the bones by strong fibers of connective tissue called tendons. • Muscle can pull when they contract, but they cannot push when they relax. They must always work in antagonistic pairs.
When the biceps muscle in the front of the upper arm contracts, the arm bends. Because the biceps mucsle flexes, the joint is called a flexor. • Wherever the biceps contracts, the triceps muscle in the back of the arm relaxes, making it possible for the arm to bend. When the triceps muscle contracts, the biceps muscle relaxes, and the arm is extended. Because the triceps muscle extends the joint, it is called an extensor.
As long as we are conscious, our skeletal muscles are never completely relaxed. Instead, our brain keeps all our muscles partly contracted. This is called muscle tone. Muscle tone keeps the muscles ready for the powerful contractions and also maintains posture.
Phosphagen System A muscle cell has some amount of ATP floating around that it can use immediately, but not very much -- only enough to last for about three seconds. To replenish the ATP levels quickly, muscle cells contain a high-energy phosphate compound called creatine phosphate. The phosphate group is removed from creatine phosphate by an enzyme called creatine kinase, and is transferred to ADP to form ATP. The cell turns ATP into ADP, and the phosphagen rapidly turns the ADP back into ATP. As the muscle continues to work, the creatine phosphate levels begin to decrease. Together, the ATP levels and creatine phosphate levels are called the phosphagen system. The phosphagen system can supply the energy needs of working muscle at a high rate, but only for 8 to 10 seconds.
Glycogen-Lactic Acid System Muscles also have big reserves of a complex carbohydrate called glycogen. Glycogen is a chain of glucose molecules. A cell splits glycogen into glucose. Then the cell uses anaerobic metabolism (anaerobic means "without oxygen") to make ATP and a byproduct called lactic acid from the glucose. About 12 chemical reactions take place to make ATP under this process, so it supplies ATP at a slower rate than the phosphagen system. The system can still act rapidly and produce enough ATP to last about 90 seconds. This system does not need oxygen, which is handy because it takes the heart and lungs some time to get their act together. It is also handy because the rapidly contracting muscle squeezes off its own blood vessels, depriving itself of oxygen-rich blood. There is a definite limit to anerobic respiration because of the lactic acid. The acid is what makes your muscles hurt. Lactic acid builds up in the muscle tissue and causes the fatigue and soreness you feel in your exercising muscles
Aerobic Respiration Aerobic Respiration • By two minutes of exercise, the body responds to supply working muscles with oxygen. When oxygen is present, glucose can be completely broken down into carbon dioxide and water in a process called aerobic respiration. The glucose can come from three different places: • remaining glycogen supplies in the muscles • breakdown of the liver's glycogen into glucose, which gets to working muscle through the bloodstream • absorption of glucose from food in the intestine, which gets to working muscle through the bloodstream • Aerobic respiration can also use fatty acids from fat reserves in muscle and the body to produce ATP. In extreme cases (like starvation), proteins can also be broken down into amino acids and used to make ATP. Aerobic respiration would use carbohydrates first, then fats and finally proteins, if necessary. Aerobic respiration takes even more chemical reactions to produce ATP than either of the above systems. Aerobic respiration produces ATP at the slowest rate of the three systems, but it can continue to supply ATP for several hours or longer, so long as the fuel supply lasts.
