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Muscle III. Smooth Muscle.

Muscle III. Smooth Muscle. Smooth Muscle. Not striated. Lack sarcomeres. Found in the walls of hollow organs. Not under voluntary control. Each cells is spindle shape. Diameter 2-10 um. Single nucleus. Capacity to divide through life. Thick filament: Myosin. Thin filament: actin.

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Muscle III. Smooth Muscle.

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  1. Muscle III.Smooth Muscle.

  2. Smooth Muscle. • Not striated. • Lack sarcomeres. • Found in the walls of hollow organs. • Not under voluntary control.

  3. Each cells is spindle shape. • Diameter 2-10 um. • Single nucleus. • Capacity to divide through life.

  4. Thick filament: Myosin. • Thin filament: actin. • Thin filaments attach to dense bodies and to the membrane. • Dense bodies linked by fibers that form cytoskeleton.

  5. Poorly developed or no SR. • No T-tube system. • Innervated by autonomic neurons. • Neurons make multiple or minimal contact with smooth muscle cells.

  6. Multi-unit: each cell receives synaptic input from one or more neurons. Each cell may contract independently. • Neurogenic.

  7. Single-unit (unitary): gap junctions permit electrical communication between cells. • Automatic (myogenic)

  8. Regulation of Smooth Muscle Contraction. • Cyclic binding and unbinding of thick and thin filaments regulated by Ca++. • Contraction and relaxation are slow and reflects changes in [Ca++]I.

  9. Electro Physiology in Smooth Muscle. • Vm in smooth muscle can change in response to neural, mechanical or hormonal stimulation. • Some develop APs that can be: • a spike. • a spike followed by a plateau.

  10. APs in Smooth Muscle. • Upstroke of AP reflects the opening of voltage gated Ca++ channels. • Ca++ not only depolarizes the fiber but also contributes to the Ca++ necessary for contraction.

  11. Some smooth muscle cells can initiate spontaneous electrical activity. • Automatic: Show pacemaker potential. • Changes in permeability of the membrane to Ca++, K+ (?)

  12. If the upstoke of the slow wave reaches threshold APs can result. • APs are not necessary to generate contraction in smooth muscle cells.

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