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CHAPTER 8 Excitation and Contraction of Smooth Muscle CONTRACTION OF SMOOTH MUSCLE...

CHAPTER 8 Excitation and Contraction of Smooth Muscle CONTRACTION OF SMOOTH MUSCLE Unitalj Smooth Muscle. Unitary smooth muscle is also Smoo uscle is composed of small fibers that are usu- called syncytial smooth muscle or visceral smooth muscle. ally to micrometers in diameter and onlY.~ The term unitary n single muscle fibers. In- micrometers in len th. In contrast, skeletal mu~ stead, it means mass of hundreds thousands of smooth are as much a O tim reater in diameter and hundreds muscle fibers that con rac o ether a a sin le unit. The of times as long. any of the same principles of contrac- fibers usually are arr; mge in s eets or un es, and their tion apply to smooth muscle as to skeletal muscle. Most cell membranes are adherent to one another at multiple important, essentially the same attractjye forces between points so that force generated in one muscle fiber can be myosin and actin filaments cause contraction in smooth transmitted to the next. In addition, the cell membranes muscle as in skeletal muscle, but t e internal h sical are joined by many gap junctiQfls through which ions can ( 1frangem3 'f smooth muscle fibe '-.. :~===Y flow freely from gne muscle cell to the next so that ac- tion potentials, or iau 001:Y uritho11t action potentials, can TYPES OF SMOOTH MUSCLE rcaxe)from one fiber tg the next and cause the wusc;le fib- -