Structure of a gap junction, a. Electron micrograph showing the plasma membranes of two adjoining cells forming a gap junction. The unit membranes (arrows) approach one another, narrowing the intercellular space to produce a 2-nm-wide gap. x76,000. b. Drawing of a gap junction, showing the membranes of adjoining cells and the structural components of the membrane that form channels or passageways between the two cells. Each passageway is formed by a circular array of six subunits, dumbbell-shaped transmembrane proteins that span the plasma membrane of each cell. These complexes,
cell membrane ,_I
connexins closed open cell membrane ,_I
connexins closed connexons membranes of adjacent cells
extracellular space b
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.