BSCI 201 Lecture 15: lecture 15- smooth muscle
6 Oct 2016
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Document Summary
Much smaller than skeletal fibers: skeletal: 10x wider and 1000x longer. Arranged in two sheets at right angles to each other. Alternating contraction/relaxation pushes stuff through lumen of smooth muscle tubes. Varicosities: bulbous swellings on nerve fibers, release nt with wide synaptic cleft. Relies on extracellular ca that comes through ca channels. Filaments run diagonally, crisscross each other, meet at dense bodies: has calmodulin instead of troponin. Mechanism of contraction: ap opens ca channels, ca goes into cell from extracellular fluid and sr, ca binds/activates calmodulin calmodulin activates myosin light chain kinase phosphorylates myosin with two phosphates and hydrolyzing atp, cross bridges cycling. Maintains same contractile force as skeletal muscle for much longer. Therefore, burns less atp for same amount of contraction. Makes atp by aerobic activity: enough to sustain smooth muscle tone constantly. Smooth muscle responds to stretch and shape change. Can generate contraction from 150% length: more than skeletal muscle (20%)
