Download excitation contraction coupling

EXCITATION CONTRACTION COUPLING
Summary of Mechanics
Muscles pull; they don’t push
Muscle lengthen by being yanked on by antagonists or gravity
Muscle force can be graded by recruitment of motor units
You activate small motor units first: the size principle
Muscle force can be graded by repetitive stimulation
Muscle force can be graded by changing length, but who cares
Muscle velocity is inversely related to muscle force: you can
be strong or fast but not both at the same time
8 Muscle power peaks at 1/3 maximum force
9 Pinnate muscle fibers develop more force at lower velocity
because of the angle
10 Muscles fatigue: they drop force on continued use
11 Muscles are heterogeneous based on contractile properties
1 Slow twitch (S)
2 Fast fatigue resistant (FR)
3 Fast Intermediate (FI)
4 Fast fatiguable (FF)
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Summary of contractile mechanisms
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Muscle cells are highly organized
Myofibrils consists of interdigitating hexagonal arrays of filaments
Thick filaments are mainly myosin: A bands
Thin filaments are actin + tropomyosin + TnI + TnC + TnT: I bands
Sliding filaments explains the length-tension curve
Cross-Bridge cycling couples ATP hydrolysis to force or shortening
Myosin isoforms have different turnover numbers
Muscles can be classified by their myosin isoforms
Type I (slow twitch)
Type IIa (fast twitch oxidative)
Type Iib (fast twitch glycolytic)
Costameres may transmit force from myofilaments to muscle
exterior through the cytoskeleton
The Ca transient trails the muscle action potential
and precedes force development
SR release and uptake activities are separate
SR Ca release produces a Ca transient and A-M activation
SR Ca reuptake shuts down A-M interaction
The Ca transient is a switch for A-M activity
Tropomyosin spreads TnC control of A-M
interaction along the actin filament
Occupancy of TnC by Ca trails the Ca transient
but precedes force development
The series-elastic model explains twitch time and tetany
Summation of Ca transients allows force
to catch up with TnC-Ca saturation