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An in-depth exploration of the structure and function of skeletal muscles, focusing on motor units, muscle fibers, myofibrils, thick and thin filaments, actin, myosin, tropomyosin, troponin, excitation-contraction coupling, and muscle contractions. It also covers the differences between type 1, 2A, and 2B muscle fibers.
Typology: Study notes
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The Skeletal Muscle - Organization
Thick filament (myosin)
Thin filament (f-actin, tropomyosin, troponin)
50-100 um 2-6 cm
The Skeletal Muscle - Organization
Excitation – Contraction Coupling I: The t-tubules and the SR
Excitation – Contraction Coupling II: The cross-bridge cycle
Attached (rest)
Head rotation and force generation
ATP-binding
ATP hydrolysis and Recock of myosin head
Cross bridge formation
Excitation – Contraction Coupling II: The cross-bridge cycle
Three types of muscle units
Type 1 Type 2A Type 2B
40 pps for 0.33 s, repeated every second
13 pps
20 pps 25 pps
large (but maybe not as large as type IIB)
fatigue resistant (though less than type I)
fast-fatigue resistant (type IIA)
Slow –twitch fibers fast-fatigable (type IIB) (type I)
The MN that innervates fast-twitch muscle fibers usually innervates many large fibers. These MN have relatively large cell bodies and large axon diameters, so they can conduce action potentials fast. (the opposite is true for those MN that innervate the small fibers)
Types of Striated Muscle/ Types of Muscle Fibers:
The Motor Units are Recruited in a fixed order
∆V = ∆I x R
The Motor Units are Recruited in a fixed order
