Smooth Muscle Physiology

As force is increased, what happens to the velocity of contraction in skeletal and smooth muscle?

1. Velocity increases in both skeletal and smooth muscle as force is increased.
2. Velocity increases in skeletal muscle, but decreases in smooth muscle when force is increased.
3. Velocity decreases in skeletal muscle, but increases in smooth muscle when force is increased.
4. Velocity decreases in both skeletal and smooth muscle as force is increased.
5. Velocity is independent of force in smooth muscle, but decreases in skeletal muscle when force is increased.
   
   Reveal Answer
   (Answer D)

Which of the following statements about smooth muscle contraction is correct?

1. A Ca2+-calmodulin complex activates the phosphatase that causes contraction of smooth muscle.
2. Unlike striated muscle, contraction of smooth muscle cells occurs when Ca2+ levels fall.
3. Phosphorylation of a myosin light chain allows actin-myosin binding in smooth muscle.
4. Dephosphorylation of a myosin light chain allows actin-myosin binding in smooth muscle.
5. Phosphorylation of an actin filament allows actin-myosin binding in smooth muscle.
   
   Reveal Answer
   (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?

1. Passive influx of calcium through Ca+2/Na+ exchangers
2. Active influx of calcium through Ca+2 ATPase
3. Active release of calcium stored in the sarcoplasmic reticulum through Ca+2 ATPase
4. Calcium-induced release of calcium stored in the sarcoplasmic reticulum
5. Direct entry of calcium through gap junctions with neighboring cells
   
   Reveal Answer
   (Answer D)

In smooth muscle cells, the modulation of strength for contraction is most directly related to which cellular mechanism?

1. The efficiency of the ATPase on the myosin head
2. The ratio of MLCK to MLCP in the cytosol
3. The amount of calmodulin available for troponin binding
4. The inherently high velocity of smooth muscle contraction
5. The ATP efficiency of the “latching” mechanism of myosin head
   
   Reveal Answer
   (Answer B)

The following best describe which type of muscle: contain sarcomeres, sarcoplasmic reticulum, and T-tubules?

1. Skeletal muscle only
2. Smooth muscle only
3. Cardiac muscle only
4. Cardiac and smooth muscle
5. Skeletal and smooth muscle
   
   Reveal Answer
   (Answer D)

An inhibitor of myosin light chain phosphatase has which effect in smooth muscle?

1. Increased sensitivity of myosin and decreased response to calcium
2. Increased sensitivity of myosin and increased response to calcium
3. Decreased sensitivity of myosin and decreased response to calcium
4. Decreased sensitivity of actin and increased response to calcium
5. Increased sensitivity of actin and decreased response to calcium
   
   Reveal Answer
   (Answer A)

Phase 2 of the diagram indicates which cardiac process?

1. Ca2+ channels are open only
2. Slow/Fast K+ channels and fast Na+ channels are open only
3. Fast Na+ channels are open and Slow/Fast K+ channels are closed
4. Slow/Fast K+ channels, Ca2+ channels, and fast Na+ channels are open
5. Slow/Fast K+ channels are open only
   
   Reveal Answer
   (Answer D)