551. Which of the following statement regarding skeletal muscle contraction is TRUE?
A. Tension of human skeletal muscle is about 3-4kg/cm2 cross sectional area.
B. Increased recruitment of motor units occur with increased voluntary movements
C. Asynchronous firing of adjacent motor units allows smooth contraction of the whole muscle
D. Tension developed in tetany is 4 times that of single muscle twitches.
E. All of the above

552. Which of the following statements regarding myocardial fibers is FALSE?
A. T system occurs at A-I Junction
B. Intercalated discs are found at Z lines
C. Intercalated discs function to transmit contractile force from 1 muscle fiber to the next
D. Gap junction between adjacent myocardial fiber gives low resistance bridges for spread of excitation from 1 muscle fiber to the next.
E. None of the above

553. Plateau & repolarization phase in myocardial AP conduction lasts:
A. 2ms
B. 20ms
C. 200ms
D. 2s
E. 20s

554. Which of the following pairing regarding myocardial conduction is INCORRECT?
A. Initial rapid depolarization -opening of voltage gated Na channels
B. Initial rapid repolarization -opening of fast K channels
C. Plateau phase -opening of slow Ca channel
D. Repolarization phase -closure of slow Ca channel & opening K channel
E. None of the above

555. Which of the following regarding myocardium is FALSE?
A. Repolarization time remains constant despite increase in heart rate.
B. Contractile response lasts 1.5 X duration of AP
C. There is no tetany in the myocardium as the relative refractory period lasts until the end of the repolarization phase.
D. Myocardium is dependent on oxidative metabolism
E. All of the above

556. Which of the following statement regarding Starling’s law of the heart is TRUE?
A. Diastolic filling of the heart determines the initial length of myocardial fiber
B. Systolic intraventricular pressure is an expression of myocardial fiber tension.
C. Systolic intraventricular pressure increases as diastolic filling of the heart increases to a critical point.
D. Overfilling of L V leads to reduction in systolic intraventricular pressure as there is disruption of myocardial fibers.
E. All of the above

557. Which of the following statements regarding myocardial metabolism is FALSE?
A. Myocardium has higher myoglobin content than skeletal muscle
B. Anaerobic metabolism in the myocardium increases from 1 to 10% during hypoxia
C. Energy produced by total anaerobic condition is enough to sustain ventricular contraction for a few hours
D. Under basal conditions, most of the caloric need of myocardium is provided by fat
E. All of the above

558. Which of the followings statements regarding smooth muscle is FALSE?
A. Smooth muscle has no troponin
B. Smooth muscle has poorly developed sarcoplasmic reticulum
C. Smooth muscle has no cross striations
D. Smooth muscle has abundant mitochondria as it is dependent on aerobic glycolysis
E. All of the above

559. The growth of smooth muscle is inhibited by:
A. Catecholamine
B. Glucocorticoid
C. Angiotensin II
D. All of the above
E. None of the above

560. The resting membrane potential of visceral smooth muscle is:
A. -5 0mV
B. -70mV
C. -90mV
D. -l lOmV
E. none of the above