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Skeletal Muscle

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Skeletal Muscle

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  1. Skeletal Muscle • Classification of muscle fiber types • Sarcomere’s length and muscle tension during contraction

  2. Skeletal muscle fibers are classified • According to contraction speed and resistance to fatigue during repeated stimulation. • 1. Fast-twitch glycolytic fibers • 2. Fast-twitch oxidative fibers • 3. Slow-twitch (oxidative) fibers

  3. Fast-twitch fibers • Fast speed of contraction • Fast myosin ATPase isoform

  4. Fast-twitch fibers • Twitch has a short duration • Ca++ is quickly removed from the cytosol during relaxation • Fast Ca++ ATPase on SR • Where? Hands (typing, piano), Eyelids (blinking).

  5. Slow-twitch fibers • For posture, standing, walking • Lift heavy loads • Contractions last a long time

  6. Fast glycolytic fibers • Fatigue quickly • Anaerobic glycolysis to generate ATP • acidosis

  7. Slow-twitch fibers • Fatigue slowly • Oxidative phosphorylation for ATP production • Blood vessels bring oxygen • Myoglobin inside the fibers. It has a high binding affinity of oxygen. • Small diameter of fibers, short distance for oxygen diffusion

  8. Fast-twitch glycolytic fibers • Fewer blood vessels • Larger muscle fibers • Quickly run out of oxygen

  9. Fast twitch oxidative • Have some myoglobin • Intermediate size • Use oxidative and glycolytic metabolism

  10. Sarcomere resting length • The length of a sarcomere in the body • This is called the optimal length • A contraction of optimal force occurs when the sarcomere is at optimal length

  11. The sliding filament theory of contraction predicts optimal length for muscle tension.

  12. Skeletal muscle physiology • Muscle contraction in the body • Summation of muscle twitches • Motor units • Muscle contraction and loads • Friday: ch. 14 Cardiavascular Physiology (After ch. 14, we’ll cover smooth muscle located at the end of ch. 12)

  13. A twitch is a single contraction/relaxation cycle

  14. The muscle does not relax completely before the second stimulus occurs, resulting In a more powerful contraction: summation Stimulus Stimulus Stimulus

  15. Motor unit • One somatic motor unit and the muscle fibers that it innervates

  16. A muscle may have many motor units of many fiber types.

  17. Recruitment of motor unit activity during muscle activity • Each motor neuron has its own threshold potential for firing action potentials • Each motor unit has its own threshold • A muscle’s activity varies with the number of motor units that are recruited • Recruitment is controlled by the nervous system

  18. Recruitment • Weak stimulus activates low threshold neurons. These regulate slow fatigue resistant fibers. • Stronger stimuli  fatigue resistant oxidative fast twitch fibers • Very strong stimuli  glycolytic fast twitch fibers

  19. Isotonic contraction – any contraction that creates a force and moves a load

  20. Isometric contraction - Create force without movement

  21. How can a muscle generate force without changing its length? • Each muscle elastic elements: • Tendons • Intracellular cytoskeletal proteins with elastic properties • Contractile proteins themselves can stretch • These are included in the term: series elastic elements.