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#muscle relaxation

3 public questions tagged with this topic.

Cytoskeleton

Which event leads to muscle relaxation?

Muscle relaxation requires rapid removal of activating calcium signal and restoration of inhibitory thin filament state to prevent ATP waste. During excitation depolarization opens dihydropyridine receptors coupled to ryanodine receptors of sarcoplasmic reticulum flooding sarcoplasm with calcium that binds troponin C or calmodulin initiating cross bridge cycling. For relaxation three mechanisms lower cytosolic calcium efficiently: sarcoplasmic reticulum Ca ATPase SERCA a P type pump hydrolyzing one ATP to transport two calcium ions into lumen against concentration gradient, plasma membrane Ca

Ref: Alberts et al., Molecular Biology of the Cell 7th ed., Chapter 16: SERCA calcium reuptake leading to muscle relaxation mechanism.

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Cytoskeleton

Which protein prevents actin-myosin interaction in relaxed muscle?

In relaxed skeletal and cardiac muscle actomyosin interaction is prevented not by direct myosin inhibition but by steric blocking of thin filament through tropomyosin troponin complex evolutionarily conserved. Tropomyosin is alpha helical coiled coil dimer about 40 nm long that polymerizes head to tail along major groove of filamentous actin spanning seven actin monomers and forming continuous cable. In low calcium near 100 nM troponin I holds tropomyosin in blocked B state covering myosin binding sites on outer domain of actin. Elevation of calcium to micromolar via ryanodine receptor release

Ref: Alberts et al., Molecular Biology of the Cell 7th ed., Chapter 16: Tropomyosin blocks myosin binding in relaxed muscle.

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