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Skeletal Muscle

Skeletal Muscle. Classification of muscle fiber types Sarcomere’s length and muscle tension during contraction. Skeletal muscle fibers are classified. According to contraction speed and resistance to fatigue during repeated stimulation. 1. Fast-twitch glycolytic fibers

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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.

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