Excitation Contraction Coupling in Smooth Muscles

As in striated muscles, the contraction of smooth muscles is triggered by a sharp rise in the Ca2+ concentration within the cytoplasm of the muscle cells. However, the sarcoplasmic reticu-lum of smooth muscles is less developed than that of skeletal muscles, and Ca2+ released from this organelle may account for

(a)

Thick filament Thin filament

Dense bodies

Intermediate filament

Thick filament Thin filament

Dense bodies

Intermediate filament

Actin (thin filament) Myosin head

Myosin (thick filament) Actin (thin filament)

■ Figure 12.33 Smooth muscle and its contractile apparatus.

(a) A photomicrograph of smooth muscle cells in the wall of a blood vessel.

(b) Arrangement of thick and thin filaments in smooth muscles. Note that dense bodies are also interconnected by intermediate fibers. (c) The myosin proteins are stacked in a different arrangement in smooth muscles than in striated muscles.

Fox: Human Physiology, I 12. Muscle: Mechanisms of I Text I © The McGraw-Hill

Eighth Edition Contraction and Neural Companies, 2003

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