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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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smooth muscle
Smooth Muscle.
  • Not striated.
  • Lack sarcomeres.
  • Found in the walls of hollow organs.
  • Not under voluntary control.
slide3
Each cells is spindle shape.
  • Diameter 2-10 um.
  • Single nucleus.
  • Capacity to divide through life.
slide4
Thick filament: Myosin.
  • Thin filament: actin.
  • Thin filaments attach to dense bodies and to the membrane.
  • Dense bodies linked by fibers that form cytoskeleton.
slide6
Poorly developed or no SR.
  • No T-tube system.
  • Innervated by autonomic neurons.
  • Neurons make multiple or minimal contact with smooth muscle cells.
slide7
Multi-unit: each cell receives synaptic input from one or more neurons. Each cell may contract independently.
  • Neurogenic.
slide8
Single-unit (unitary): gap junctions permit electrical communication between cells.
  • Automatic (myogenic)
regulation of smooth muscle contraction
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.
electro physiology in smooth muscle
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.
aps in smooth muscle
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.
slide14
Some smooth muscle cells can initiate spontaneous electrical activity.
  • Automatic: Show pacemaker potential.
  • Changes in permeability of the membrane to Ca++, K+ (?)
slide15
If the upstoke of the slow wave reaches threshold APs can result.
  • APs are not necessary to generate contraction in smooth muscle cells.