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Phys Lect 15
| Question | Answer |
|---|---|
| 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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