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Skeletal Muscle - Tension

Skeletal Muscle - Tension. (2) active tension (muscle activation) Excitation-contraction coupling Ca 2+ , ATP Muscle size (cross-sectional area) Muscle length (stretch) Rate coding (frequency modulation) & motor unit recruitment Shortening velocity Temperature Fiber-type Reflexes.

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Skeletal Muscle - Tension

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  1. Skeletal Muscle - Tension • (2) active tension (muscle activation) • Excitation-contraction coupling • Ca2+, ATP • Muscle size (cross-sectional area) • Muscle length (stretch) • Rate coding (frequency modulation) & motor unit recruitment • Shortening velocity • Temperature • Fiber-type • Reflexes

  2. Motor Units • Contains the motor neuron • And all the muscle fibers it innervates • The same muscle within a single motor unit have the same: • Histology • Biochemistry • Slow-twitch, • Fast twitch motor units • motor end plate

  3. Motor Unit

  4. Illustration of the Neuromuscular Junction

  5. Motor Units (continued) • Each axon will split up to contact individual muscle fibers • Motor End Plate (neuromuscular junction) • contact between a motor neuron and muscle cells (fibers) • In humans there is one motor end plate per skeletal muscle fiber

  6. Motor Units (continued) • There may be 10-2000 muscle fibers in a motor unit • Fine movements (eyes, fingers, etc.) • Small number of muscle fibers • Increase # of motor units • Gross movements (quads, gastroc, etc.) • Large # of fibers

  7. Rate coding and motor unit recruitment • Need to control force generation of muscle to perform movement correctly and safely • Ex. Lifting a 50lb bag of sand vs. lifting a pencil • To increase tension generation we can: • (1) increase recruitment of motor units • (2) increase the frequency of APs down the motor neuron: • Frequency modulation (FM) • Efficient, reduces noise (errors) • digital • Summation • Increase Ca++ levels

  8. Rate coding (FM) and control of muscle force • increase the frequency of APs down the motor neuron: All APs in muscle and motor neuron look alike

  9. Rate coding (FM) and control of muscle force • increase the frequency of APs down the motor neuron: • Summation - increase Ca++ levels • Tetanus ~ 4 x twitch force

  10. FM & control of muscle force • Summation - increase Ca++ levels • Fatigue alters response to increasing freq. of APs

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