Skeletal Muscle

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Skeletal Muscle

• Classification of muscle fiber types
• Sarcomeres length and muscle tension during
  contraction

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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

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Fast-twitch fibers

• Fast speed of contraction
• Fast myosin ATPase isoform

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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).

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Slow-twitch fibers

• For posture, standing, walking
• Lift heavy loads
• Contractions last a long time

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Fast glycolytic fibers

• Fatigue quickly
• Anaerobic glycolysis to generate ATP
• acidosis

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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

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Fast-twitch glycolytic fibers

• Fewer blood vessels
• Larger muscle fibers
• Quickly run out of oxygen

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Fast twitch oxidative

• Have some myoglobin
• Intermediate size
• Use oxidative and glycolytic metabolism

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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

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