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KIN 3600

lec 20

Excitation – contraction Excitation of muscle coupled with concentration by regulation of sarcoplasmic Ca++ concentration
Coupling agent Calcium
Since the release of calcium is faster than the reuptake muscle shortening is faster than the relaxation
Rate of increase calcium comes in the cell faster than the rate of decrease calcium leaving the cell
High calcium = Continuous contraction
Recycle contractions cycle Resting state -Cocked & Energy used (Ca++) Stimulation -Ca++ release from SR Formation - Strong bond Power stroke - Release ADP Cross bridge completion - ATP binds to bridge & Form weak bond Resting state - Re-cocked & Ca++ back to SR
Muscle Twitch - 1 twitch = 1 single contraction - Short stimulation
3 phases of muscle twitch 1. latent period 2. contraction phase 3. relaxation phase
PHASE 1 - Latent Period (Electromechanical delay) - 5ms - Stimulated but did not respond
PHASE 2 - Contraction phase - (40ms)
PHASE 3 - Relaxation phase - (50ms) - Longer
Refractory period - 5ms - Muscle does not respond to simulation
Why do muscles contract faster than the relaxation phase? Ca++ influx is faster than the outflux
Muscles responsible for fast movements Short twitch time
Muscles responsible for slow movements Long twitch time
Twitch Summation stimulation of muscle fiber before the completion of previous twitch results in a stronger contraction - Ca++ is being pumped & pumped
Underlying mechanism of Twitch Summation - Pre-stretching of SEC by the first twitch - Not enough time available to pump all Ca++ back to SR & Out of the cell – resulting progressive increase in sarcoplasmic Ca++ concentration
Wave summation Progressive ^ sarcoplasmic Ca++ without all getting pumped back into SR
Fused tetanus - Continuous contraction with no relation - No change in sarcoplasmic & Ca++ concentration
All in-vivo muscular contractions are tetanic contraction
Treppe Effect Stimulate muscle with low energy frequencies not to cause tetanic contraction (5Hz)
Treppe Effect responds by - Progressive increment in tension for up to 30-40 contractions - Failure to relax completely
Treppe Effect caused by - ^ Na+ & K+ concentration or sarcoplasm, ^ rate of ca++ release of SR - Progressive influx of Ca++ into the cell - Lack of time available to pump the Ca++ back into the SR & out of the cell
Types of muscle fibers -Slow Twitch Oxidative (ST, SO, R) or Type I -Fast twitch oxidative – Glycolytic (FOG) or Type IIA -Fast twitch glycolytic (FT, FG) or Type IIX or Type IIB (rats)
The main characteristics of Type IIX fibers -High contractile speed (2-3 times faster than ST) -High activity of myosin (ATPase, CPK, & Anaerobic Glycolytic enzymes) -Larger diameter -High maximal tension (2-3x higher than ST) -High capacity for anaerobic glycogenolysis -SR network
Calculation of Specific Tension cross-sectional area / Force produced
Created by: rmart11