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Muscles - part 4

Muscles - part 4. Muscle Contraction. Providing Energy for Muscle Contraction. Muscles store very limited supplies of ATP - 4 to 6 sec ATP is the only energy source used directly to power muscle activity ATP is regenerated continuously for continuous muscle contraction .

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Muscles - part 4

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  1. Muscles - part 4 Muscle Contraction

  2. Providing Energy for Muscle Contraction • Muscles store very limited supplies of ATP - 4 to 6 sec • ATP is the only energy source used directly to power muscle activity • ATP is regenerated continuously for continuous muscle contraction

  3. ATP Regeneration • Working Muscles Use Three Pathways for ATP Regeneration: • Direct phosphorylation of ADP by creatine phosphate • Aerobic respiration • Anaerobic glycolysis and lactic acid formation

  4. Direct Phosphorylation of ADP by Creatine Phosphate • creatine phosphate (CP) a unique high-energy molecule is found in muscle fibers but not other cell types. • CP transfers a high-energy phosphate group to ADP, regenerating more ATP in a fraction of a second. • CP supplies are exhausted in about 20 seconds.

  5. Aerobic Respiration • Occurs in the mitochondria • a series of metabolic pathways that use oxygen. • Glucose is broken down completely to CO2and H2O • Some energy that is released as bonds are broken is captured in the bonds of ATP molecules.

  6. Aerobic Respiration • Provides a rich ATP harvest • It requires continuous delivery of O2 and nutrient fuels to the muscle to keep it going • It is fairly slow • At rest and during light exercise, ~95% of the ATP used for muscle activity comes from aerobic respiration.

  7. Anaerobic Glycolysis and Lactic Acid Formation • The sluggish aerobic mechanisms cannot keep up with the demands for ATP when: • Muscle activity is intense or • Oxygen and glucose delivery is inadequate to meet the needs of working muscles • Under these conditions, the pyruvic acid generated during glycolysis is converted to lactic acid, and the overall process is referred to as anaerobic glycolysis.

  8. Anerobic Glycolysis and Lactic Acid Formation • Produces about 5% as much ATP from each glucose molecule as aerobic respiration. • It is ~ 2 ½ times faster than aerobic respiration. • It can provide most of the ATP needed for 30 to 60 seconds of strenuous muscle activity.

  9. Shortcomings of Anaerobic Glycolysis • It uses huge amounts of glucose for a small ATP harvest. • Accumulating lactic acid promotes muscle fatigue and muscle soreness.

  10. Muscle Fatigue • occurs when a muscle is unable to contract even though it is still being stimulated. • exercise muscles strenuously for a long time • Without rest, an active or working muscle begins to tire and contracts more weakly until it finally ceases reacting and stops contracting.

  11. Muscle Fatigue • True muscle fatigue rarely occurs in most of us • we feel fatigued long before it happens and slow down or stop activity. • More common in marathon runners • Many have literally collapsed when their muscles became fatigued and could no longer work.

  12. Oxygen Debt • Muscle fatigue is believed to result from O2 debt during prolonged exercise • A person is not able to take in O2 fast enough to keep the muscles supplied with all the O2 they need when they are working vigorously.

  13. Oxygen Debt • The work that a muscle can do and how long it can work without becoming fatigued depends on how good its blood supply is.

  14. Results of Oxygen Debt • Lack of O2 to muscles---> lactic acid begins to accumulate in the muscle. • the muscle ATP supply starts to run low. • The increasing acidity and the lack of ATP cause the muscle to contract less and less effectively and finally stop contracting altogether.

  15. Oxygen Debt • Must be paid back whether or not muscle is fatigued • During the recovery period after exercise, a person breathes rapidly and deeply. • This continues until the muscles have received the amount of O2 needed to get rid of the accumulated lactic acid and make ATP and CP reserves.

  16. Discussion break • Discuss – tell about a time when you pushed your muscles too far. Have you experience true muscle fatigue? • What exercise has given you the most muscle soreness? How long did it take to heal?

  17. Types of Muscle Contractions • Isotonic Contractions • The myofilaments are successful in their sliding movements, the muscle shortens, and movements occurs. • Examples: Bending the knee, smiling, rotating the arm • 2. Isometric Contractions • Contractions in which the muscles do not shorten. • Tension develops in the muscle and it attempts to slide the filaments filaments • Example: When you push against a wall

  18. Muscle Tone • Muscle Tone – The state of continuous partial contractions. • Is the result of different motor units (which are scattered through the muscle) being stimulated by the nervous system in a systematic way.

  19. Muscle Tone • Even when a muscle is voluntarily relaxed some of its fibers are contracting – first one group and then another. • contraction is not visible, as a result the muscle remains firm, healthy, and constantly ready for action.

  20. Flaccid • If the nerve supply to a muscle is destroyed, the muscle is no longer stimulated and it loses tone and becomes paralyzed. • Soon after it becomes flaccid (soft and flabby) and begins to atrophy (waste away).

  21. Use It or Lose It • Muscle inactivity (due to loss of nerve supply immobilization, or whatever the cause) always leads to muscle weakness and wasting! • Regular exercise increases muscle size, strength, and endurance.

  22. Aerobic (Endurance) Exercise • Examples: Walking, jogging, cycling, swimming • Result: Stronger, more flexible muscles with greater resistance to fatigue. • These changes come about because the blood supply to the muscles increases and more mitochondria form in the individual muscle cells and can store more oxygen. • Does not cause the muscles to increase much in size

  23. Other Adaptations from Aerobic Exercise • Makes overall body metabolism more efficient • Improves digestion • Enhances neuromuscular coordination • Makes the skeleton stronger • The heart enlarges (hypertrophies) so that more blood is pumped out with each beat • Fat deposits are cleared from the blood vessel walls • Lungs become more efficient in gas exchange

  24. Resistance • Isometric exercises in which the muscles are pitted against some immoveable object (or nearly so). • Require very little time and little or no special equipment • The key is forcing the muscles to contract with as much force as possible.

  25. Results of Resistance Training • Results in increased muscle size and strength. • Due to enlargement of individual muscle cells (they make more contractile filaments) • Not due to an increase in their number.

  26. Know Your Exercise Goals • Lifting weights will not improve endurance for a marathon. • Jogging will do little to improve your muscle definition for competing in Mr. Muscle contest. • The best exercise program is one that includes both types of exercise.

  27. Discussion break • Do you exercise regularly? Are you involved in sports? • What is your favorite kind of exercise? • If you don’t exercise, why not?

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