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Phys Lect 15

Innervation of Smooth Muscle ANS. Parasymp, symp, and Enteric (controls the gut motility and integrity).
Single Unit Smooth Muscle Composed of several muscle cells, but functionally acts as one unit due to GAP JUNCTIONS. **Produces PHASIC acivity
Multi-unit Smooth Muscle Cells are independently controlled by specific nerves (Rarely gap junctions). **Produce constant/tonic activity. Seen in areas of fine control since stimulation can be increased or decreased.
Relationship between Size and electrical coupling in a functional unit of smooth muscle Size is directly dependent on how well coupled the smooth muscles cells are. **Ex: Bladder is one big functional unit(well coupled)
Dense bodies Serve as anchors for Actin and Myosin filaments in smooth muscle. They are connected to other dense bodies by INTERMEDIATE FILAMENTS. **The Actin & Myosin are obliquely arranged
Caveoli Invaginations of the smooth muscle cell membrane that contain a high density of membrane transporters. Responsible for activating SR in smooth muscle **Smooth muscle equivalent to T-tubules.
Fiber orientation in smooth muscle Oriented to suit its function. Examples: 1.Circumfrentially (BL vessels, airways): can alter the diameter. 2.Circumfrential & Longitudinal (GI): can mix the contractions to produce movement (peristalsis)
Tonic Contractions constant basal level of contractile activity that can be Inc/Dec occasionally. Can be independent to Em, in response to hormones.(see with multi-unit for fine control). **Ex: Sphincters, BL vessels.
Phasic Contractions Intermitten contractions with periods of no conractions. Very dependent on Em and APs. Summation is possible. (see with single-unit formed by gap junctions). **Ex: Intestines, Bladder
Electrical activity patterns: Phasic contractions Generated by APs from voltage-gated Ca channels.
Electrical activity patterns: Tonic contractions Generated by: 1.Graded changes in Em. 2.Independent of Em
What Ion current contributes to the upstroke APs in smooth muscle? Ca2+
Ca2+ Vs. Na+ voltage-gated channels Ca2+ channels open slower (slower activation) but stay open longer.
Dual role of Ca2+ channels in smooth muscle 1.Depolarization (since they are a + influx into the cell). 2.Contraction initiation (once the Ca2+ has rushed into the cell, it can activate MLCK).
Slow waves of phasic smooth muscle contraction Ca-activated K+ Channels: 1.APs are generated amidst slow waves by the opening of Ca-channels. 2.Depolar caused by Inc Intracellular Ca opens K+ channels. 3.Repolarization causes Ca-channels to close. 4.[Ca+] declines, closing K+ channels
Neurohormonal Agents Can induce tonic contractile changes independent of Em. They can cause a change in 'tone' which is modulated by graded Em changes. **Bind to G-protein and induce IP3 from Phospholipase C
3 ways to increase Intracellular Ca2+ in smooth muscle 1.Voltage-gated Ca-Channels. 2.Ligand-gated Ca-Channels. 3.Secondary messanger IP3 generation (release from SR).
Pharmacomechanical coupling Mechanisms that modulate contraction without changing Em (tonic contractions). 1.IP3 generation. 2.Modulation of MLCP. 3.Activation of store-operated Ca-Channels (allows an increase in Ca+ when SR stores are low).
Created by: WeeG



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