Smooth Muscle Physiology
As force is increased, what happens to the velocity of contraction in skeletal and smooth muscle?
- Velocity increases in both skeletal and smooth muscle as force is increased.
- Velocity increases in skeletal muscle, but decreases in smooth muscle when force is increased.
- Velocity decreases in skeletal muscle, but increases in smooth muscle when force is increased.
- Velocity decreases in both skeletal and smooth muscle as force is increased.
- Velocity is independent of force in smooth muscle, but decreases in skeletal muscle when force is increased.(Answer D)
Which of the following statements about smooth muscle contraction is correct?
- A Ca2+-calmodulin complex activates the phosphatase that causes contraction of smooth muscle.
- Unlike striated muscle, contraction of smooth muscle cells occurs when Ca2+ levels fall.
- Phosphorylation of a myosin light chain allows actin-myosin binding in smooth muscle.
- Dephosphorylation of a myosin light chain allows actin-myosin binding in smooth muscle.
- Phosphorylation of an actin filament allows actin-myosin binding in smooth muscle.(Answer C: Nerve impulses cause Ca2+ gates in the plasma membrane to open allowing Ca2+ to enter the cell. Ca2+ activates a myosin light chain kinase, via a protein called calmodulin. The kinase phosphorylates the myosin light chain abolishing the inhibitory effect of myosin binding to actin. Contraction occurs.)
Edelfosine, a PLC antagonist, inhibits the release of stored cellular calcium via the IP3 pathway. In a multi-unit smooth muscle cell exposed to a similar agent, by what mechanism would the muscle cell rely on to increase cytosolic calcium levels?
- Passive influx of calcium through Ca+2/Na+ exchangers
- Active influx of calcium through Ca+2 ATPase
- Active release of calcium stored in the sarcoplasmic reticulum through Ca+2 ATPase
- Calcium-induced release of calcium stored in the sarcoplasmic reticulum
- Direct entry of calcium through gap junctions with neighboring cells(Answer D)
In smooth muscle cells, the modulation of strength for contraction is most directly related to which cellular mechanism?
- The efficiency of the ATPase on the myosin head
- The ratio of MLCK to MLCP in the cytosol
- The amount of calmodulin available for troponin binding
- The inherently high velocity of smooth muscle contraction
- The ATP efficiency of the “latching” mechanism of myosin head(Answer B)
The following best describe which type of muscle: contain sarcomeres, sarcoplasmic reticulum, and T-tubules?
- Skeletal muscle only
- Smooth muscle only
- Cardiac muscle only
- Cardiac and smooth muscle
- Skeletal and smooth muscle(Answer D)
An inhibitor of myosin light chain phosphatase has which effect in smooth muscle?
- Increased sensitivity of myosin and decreased response to calcium
- Increased sensitivity of myosin and increased response to calcium
- Decreased sensitivity of myosin and decreased response to calcium
- Decreased sensitivity of actin and increased response to calcium
- Increased sensitivity of actin and decreased response to calcium(Answer A)
Phase 2 of the diagram indicates which cardiac process?
- Ca2+ channels are open only
- Slow/Fast K+ channels and fast Na+ channels are open only
- Fast Na+ channels are open and Slow/Fast K+ channels are closed
- Slow/Fast K+ channels, Ca2+ channels, and fast Na+ channels are open
- Slow/Fast K+ channels are open only(Answer D)