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skeletal muscle

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actin and myosin filaments interact to generate force

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actin

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participates in many important cellular processes including muscle contraction, cell division cell signalling, and the establishment and maintenance of cell junctions and cell shape

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myosins

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ATP-dependent motor proteins best known for their role in muscle contraction and their involvement in a wide range of other eukaryotic motility (movement) processes

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eukaryote [yoo-KAIR-ee-oht]

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an organism whose cells contain a nucleus and other structures enclosed within membranes

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muscle contraction

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transmission of the electrical impulse across the neuromuscular junction is mediated by the transmitter acetycholine [ah-see-ta-KOHL-een]

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the excitation of the motor nerve is transferred to excitation of the muscle membrane as well as the extension of the muscle membrane into the muscle, the T-tubule.

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calcium releases into the sarcoplasm (sarcoplasm is comparable to the cytoplasm of other cells, but it houses unusually large amounts of oxygen binding proteins). The calcium concentration in sarcoplasma is also a special element of the muscular fiber by means of which the contractions take place

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calcium binds with Troponin C which allows the interaction of actin and myosin which produces force

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Troponin C is part of the Troponin complex, three regulatory proteins (troponin C, troponin I and troponin T) which are integral to muscle contraction in skeletal and cardiac muscle, but not smooth muscle

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ATP (adenonsine triphosphate)

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high energy molecule

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utilized at various steps and very important in muscle contraction

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involves hydrolysis (cleavage of chemical bonds by the addition of water)

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many processes within muscle contraction dependent on ATP

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during relaxation, calcium is pumped back into the cytoplasmic reticulum

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cytoplasm: the gel-like substance enclosed within the cell membrane

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reticulum: compartment

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ATPase [ATP-ace]

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an enzyme that catalyzes the decomposition of ATP

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ATP during exercise

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exercise intensity is usually measured in maximal oxygen uptake, or VO2 max

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VO2 max

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V = volume

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O = oxygen

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max = maximum

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the maximum capacity of an individual's body to transport and use oxygen during incremental exercise, which reflects the physical fitness of the individual

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up to 100% of VO2 max is largely aerobic

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over 100% VO2 max, then non-aerobic energy systems are contributing to the power generation

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75% of VO2 max = moderate to intense exercise

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if you relied solely on the ATP within your muscle, you would only be able to exercise at this rate for about 15 seconds

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if you increase it to 140% VO2 max, you would last for about 6 seconds

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therefore, other metabolic pathways are activated to generate ATP to generate muscle contraction

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substrate level phosphorylation

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ATP is regenerated by the interactions and exchange of phosphate

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anaerobic glycolysis: transformation of glucose to pyruvate when limited amounts of oxygen (O2) are available

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Pyruvic acid: supplies energy to living cells through the citric acid cycle when oxygen is present, and alternatively ferments to produce lactic acid when oxygen is lacking

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oxidative phosphorylation

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the metabolic pathway in which the mitochondria in cells use their structure, enzymes, and energy released by the oxidation of nutrients to reform ATP.

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carbohydrate and fat drives the re-synthesis of ATP

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overview of skeletal muscle energy metabolism

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utilization of ATP

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creatine phosphate serves as a buffer during levels of intense exercise

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creatine phosphate

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facilitates transport of high energy phosphate from mitochondria

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carbohydrates are degraded through glycolisis and converted to lactate or into the mitochondria which generates ATP

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fat is another important fuel during exercise

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fatty acyl CoAs [koh-ayz] transfer into the mitochondria

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beta oxidation

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the process by which fatty acid molecules are broken down in the mitochondria to generate acetyl-coA, which enters the citric acid cycle, and NADH and FADH2, which are used by the electron transport chain