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6b. The Muscular System

6b. The Muscular System. Contraction of a Skeletal Muscle. Muscle fiber contraction is “all or none” Within a skeletal muscle, not all fibers may be stimulated during the same interval Different combinations of muscle fiber contractions may give differing responses

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6b. The Muscular System

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  1. 6b. The Muscular System

  2. Contraction of a Skeletal Muscle • Muscle fiber contraction is “all or none” • Within a skeletal muscle, not all fibers may be stimulated during the same interval • Different combinations of muscle fiber contractions may give differing responses • Graded responses – different degrees of skeletal muscle shortening

  3. Contraction of Skeletal Muscle • Graded responses can be produced by changing • The frequency of muscle stimulation • The number of muscle cells being stimulated at one time

  4. Types of Graded Responses • Twitch • Single, brief contraction • Not a normal muscle function Figure 6.9a–b

  5. Types of Graded Responses • Tetanus (summing of contractions) • One contraction is immediately followed by another • The muscle does not completely return to a resting state • The effects are added Figure 6.9a–b

  6. Types of Graded Responses

  7. Types of Graded Responses • Unfused (incomplete) tetanus • Some relaxation occurs between contractions • The results are summed Figure 6.9c–d

  8. Types of Graded Responses

  9. Types of Graded Responses • Fused (complete) tetanus • No evidence of relaxation before the following contractions • The result is a sustained muscle contraction Figure 6.9c–d

  10. Types of Graded Responses

  11. Muscle Response to Strong Stimuli • Muscle force depends upon the number of fibers stimulated • More fibers contracting results in greater muscle tension • Muscles can continue to contract unless they run out of energy

  12. Don’t you wish you were there?

  13. Energy for Muscle Contraction • Initially, muscles used stored ATP for energy • Bonds of ATP are broken to release energy • Only 4-6 seconds worth of ATP is stored by muscles • After this initial time, other pathways must be utilized to produce ATP

  14. Energy for Muscle Contraction • Direct phosphorylation OF ADP by creatine phosphate (CP) • Muscle cells store (CP) • CP is a high-energy molecule • After ATP is depleted, ADP is left • CP transfers energy to ADP, to regenerate ATP • CP supplies are exhausted in less than 15 seconds Figure 6.10a

  15. Energy for Muscle Contraction

  16. Energy for Muscle Contraction • Aerobic Respiration • Series of metabolic pathways that occur in the mitochondria • Glucose is broken down to carbon dioxide and water, releasing ATP • Energy captured in bonds of ATP  36 ATP/glucose • This is a slower reaction that requires continuous oxygen • A series of metabolic pathways occur in the mitochondria Figure 6.10b

  17. Energy for Muscle Contraction

  18. Energy for Muscle Contraction • Anaerobic glycolysis and lactic acid formation • Reaction that breaks down glucose without oxygen • Glucose is broken down to pyruvic acid to produce some ATP (2 ATP/glucose) • Pyruvic acid is converted to lactic acid; • This reaction is not as efficient, but is fast • Huge amounts of glucose are needed • Lactic acid produces muscle fatigue Figure 6.10c

  19. Energy for Muscle Contraction

  20. Muscle Fatigue and Oxygen Debt • When a muscle is fatigued, it is unable to contract even with a stimulus • The common reason for muscle fatigue is oxygen debt • Oxygen must be “repaid” to tissue to remove oxygen deficit • Oxygen is required to get rid of accumulated lactic acid • Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less

  21. Types of Muscle Contractions • Isotonic contractions = same tone or tension • Myofilaments are able to slide past each other during contractions • The muscle shortens • i.e. bending knee, rotating arm • Isometric contractions = same length • Tension in the muscles increases • The muscle is unable to shorten • i.e. pushing against a wall

  22. Muscle Tone • Some fibers are contracted even in a relaxed muscle • Different fibers contract at different times to provide muscle tone • Keeps muscles firm & healthy • The process of stimulating various fibers is under involuntary control

  23. Effect of Exercise on Muscles • Exercise increases muscle size, strength, and endurance • Aerobic (endurance) exercise (biking, jogging) results in stronger, more flexible muscles with greater resistance to fatigue • Makes body metabolism more efficient • Improves digestion, coordination • Resistance (isometric) exercise (weight lifting) increases muscle size and strength

  24. Effect of Exercise on Muscles

  25. Effects of Exercise on Muscle • Results of increased muscle use • Increase in muscle size • Increase in muscle strength • Increase in muscle efficiency • Muscle becomes more fatigue resistant

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