Cardiac Membrane Potentials

Question 1

The conduction of electrical impulse from endocardium to epicardium is mainly through __________ cell.

Answer 1

Contractile muscle cells NOT specialized fibers

Question 2

At what voltage are the funny currents activated?

Answer 2

-50 mV

Question 3

Whata re the basic mechanisms of changes in sinus node automaticity?

Answer 3

• MDP
  
  • ​As the MDP becomes more negative it will take more time for the SDD to reach threshold and therefore increases the diastolic time (bradycardia)
• SDD slope
  
  • ​As the slope increases less time is needed to reach threshold, and therefore decreases the diastolic time (tachycardia)
• Threshold potential
  
  • as it becoems less negative, diastolic time is increased

Question 4

How can tachycardias produce AV block?

Answer 4

• The refractoryp period of AV node cells is much longer than the action potential duration.
• With substantial increase in heart rate, the interval between action potentials may shorten to a degree where they fall within the preceding refractory period.
• Thus, the AV conduction will be slowed down or blocked

Question 5

The APA is equivalent to the sum of the _________ and the _________.

Answer 5

Resting membrane potential

Overshoot