L 2 & 3 , Cardiac properties , Physiology

L2 Cardiac properties

 Lecture video

L3 Heart as a pump

Lecture video

الرسمة اللى اتشرح عليها


The phase indicated by the arrow is characterized by which of the following:

1- At which membrane potential is zero

A.   There is small inflow of Ca+2 and Na+

B.    It’s large and fast repolarization phase

C.    It is caused by increase in K+ outflow 

D.    B and C

E.     C and D

2- During which phase the Cl- ions inflow is increased:

A. 1

B.  2

C.  3

D. 4

3- The action potential of the cardiac muscle is characterized by the presence of plateau which

A. It results from an inflow of Cl- and outflow of bicarbonate ions

B.  It results from a balance between Ca++ influx and K+ efflux

C.  In the atrial muscle it reached 300msec

D. In the ventricular muscle it reached 100msec


4- One of the characteristics of cardiac muscle is that it has excitability which of the following best describes this characteristic

A. Contracts when stimulated

B.  Has local electrical charges that move along the muscle fiber

C.  Only pull; they cannot push

D. Can stretch when needed

E.  None of the above


5-About the absolute refractory period of the heart which is incorrect

A. It’s the phase of cardiac cycle when the heart cannot respond to any stimulus however strong

B.  Is shorter than the absolute refractory period in skeletal muscle

C.  Corresponds approximately in time withthe duration of plateau

D. Lasts approximately as long as the cardiac contraction


 6-In the second half of diastole

A. The excitability of the cardiac muscle is zero

B.  The cardiac muscle needs more than threshold stimulus

C.  The cardiac muscle can be stimulated by a sub threshold stimulus

D. Stimulation of cardiac muscle during this period causes tetanization


7-Repolarization of the SAN fibers is caused mainly by

A. Activation of Ca+2/Na+ channels

B.  Opening of K+ ion channels which allow K+ ions to diffuse out of the membrane

C.  Continues leakage of SAN fibers to Na+ ion

D. Decrease permeability of the automatic cells to K+ ion


8-Which of the following are trueabout pacemaker of the heart:

A. They are automatic cells of most rapid rate of diastolic depolarization

B.  They are responsible for determine the heart rate

C.  The normal pacemaker of the heart is the SAN

D. All of the above


9-The SAN is the heart’s normal pacemaker because:

A. It has the fastest rate of rhythmicity

B.  It has both sympathetic and parasympathetic innervation

C.  It lies in the right atrium

D. Activation of K+ channels occurs more rapidly in this region than elsewhere in the heart


10-The ability of the cardiac muscle to initiate its beat is considered asneurogenic

A.             True

B.              False


11-All of the following are true about RMP of automatic cells except:

A.             It’s called diastolic depolarization

B.              It’s caused due to increase permeability to Na+ ions

C.              It coincides with ventricular systole

D.             All of the above are true


12-The phase indicated by the arrow is characterized by which of the following:


A.             It’s caused by decrese permeability of K+ ion

B.              It’s slow upstroke that reaches +10 mv

C.              Ca+2 / Na+ channels become inactivated

D.             None of the above

 13-Digitalis is a drug increasing myocardial contractility. Which of the following is true about mechanism of action of digitalis: 

A.             Increasing number of Beta adrenergic receptors

B.              Blocking Na+/K+ ATPase

C.              Increase formation of CAMP

D.             Blocking Na+/Ca++ exchanger


14-Which of the following occurs in the sympathetic stimulation:

A.             Stimulation of Gi Ptn

B.              Phosphorylation of Ca++ channels

C.              Dephosphorylation of Ca++ channels

D.             Inhibition of CAMP

E.              None of the above


15-Sympathetic stimulation depend on presence of which of the following receptors:

A.             Muscarinic receptors

B.              Beta 1 receptors

C.              Beta 2 receptors

D.             None of the above


16-Which of the following chemicals factors affecting the number of Beta receptors:

A.             Adrenaline

B.              Digitalis

C.              Thyroxin

D.             Xanthines


17-Contractile response of cardiac muscle

A.             Obey all or none law

B.              Starts at the same time of electric excitation

C.              Is triggered by the release of Ca++ from SR as in skeletal muscle

D.             Last for the same time as its action potential


18-Contractile response of cardiac muscle

A.             Starts at the same time of electric excitation 

B.              Is triggered by the ionic Calcium from SR as in skletal muscle

C.              Reaches its peak tension during the last third of the plateau of AP

D.             Lasts for the same time as its action potential and not obey the all or none law


19-Myocardial contractility is best correlated with the Intracellular concentration of:

A.             Na+

B.              K+

C.              Ca++

D.             KCI

NB : Increase in cardiac contractility “+ve inotropic”

       Decrease in cardiac contractility “-ve inotropic”


20-The following agents have +ve inotropic on the heart except

A.             Nor epinephrine    

B.              Digitalis

C.              Glucagon     

D.             Acetylcholine 


21-The important function of cardiac purkinje system is to

A.             Slow the conduction of impulses

B.              Increase the conduction of impulses inatria

C.              Amplify the cardiac impulses

D.             Increase the force of ventricular contraction


22-Chronotropism refers to:

A. Rhythmicity

B. Conductivity

C. Excitability

D. Contractility


23- Slowest conduction occurs in:

A. Atrium

B. AV node

C. Bundle of His

D. Purkinje fibers

E. Ventricular muscle


24-Parasympathetic produce all  of the following except: 

A. decrease heart rate

B. Decrease atrial contractility

C. Increase ventricular contractility

D. Decrease rate of discharge from SAN


  1. F                                                     
  2. B                                                     
  3. B
  4. A
  5. B
  6. C
  7. B
  8. D
  9. A
  10. B
  11. C
  12. B
  13. B
  14. B
  15. B
  16. C
  17. A
  18. C
  19. C
  20. D
  21. D
  22. D
  23. B
  24. C