Question

Briefly describe how contraction and relaxation in smooth muscle differs from contraction and relaxation in skeletal and cardiac muscle.

Answer 1

• Unlike skeletal muscle, smooth muscle does not contain the calcium-binding protein troponin. Due to absence of troponin, cross-bridge formation is not regulated by the troponin-tropomyosin complex but instead by the regulatory protein calmodulin.
• Unlike skeletal muscles, smooth muscles lack myofibrils.
• Unlike skeletal muscles, smooth muscle fibres are resistant to fatigue.
• Smooth muscles have a slower contraction speed due to

1. Slower diffusion rate of calcium ions
2. Rate of action potential propagation
3. Slower cross-bridge forming.

• Smooth muscles can contract over a wider range of resting lengths because the actin and myosin filaments in smooth muscle are not as rigidly organized as those in skeletal muscle.