How Muscles Contract

How Muscles Contract

A & P

Other Facts about Twitch Fibers

• Humans have both types of fibers
• Distribution of fibers is genetically determined
• Neither type can be converted but capacity can be increased through intense exercise

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Fast Twitch Fibers

• Contract quickly
• Fatigue quickly
• Sprinters
• Use anaerobic respiration
• Energy from glycogen
• White meat

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
• Anaerobic glycolysis
• Reaction that breaks down glucose without oxygen
• Glucose is broken down to pyruvic acid to produce some ATP
• Pyruvic acid is converted to lactic acid

The Sliding Filament Theory of Muscle Contraction

Slow Twitch Fibers

• Contract slowly
• Fatigue slowly
• Long distance runners
• Use aerobic respiration
• Energy from fat
• Dark meat
• Red or dark because of myoglobin
• Myoglobin: helps O2 bind in muscle

• Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament
• Myosin heads then bind to the next site of the thin filament
• This continued action causes a sliding of the myosin along the actin
• The result is that the muscle is shortened (contracted)
• 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

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