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25 Cards in this Set

  • Front
  • Back
What does cellular contraction depend on?
Action potentials
Cardiac contraction depends on
Coordinated excitation.
Coordinated excitation depends on
A pacemaker and conduction systems.
What is special about APs in the heart?
They vary in shape in diff. regions of heart.
What is the absolute refractory period?
No response to any further stimulus.It is from fast upstroke to end of plateau(Na+ channels close for 100 ms)
What is the relative refractory period?
If stimulate cardiomyocyte hard enough-from end of plateau to after of repolarisation.
What is the physiological purpose of refractory period?
Ensures period of relaxation(filling)
What is the cardiac pacemaker?
SA node in the right atrium.
-specialised muscle cells
-UNSTABLE resting mb potential.
-diff. ionic channels conformation than in ventr. cardiomyocytes.
What is special about cardiac pacemaker cell?
No electrical impulses needed to generate AP.(but input from brain via ANS can alter rate)
What are the 3 ways to alter rate of firing of AP?
-Increase slope
-lower threshold
-move lower mb potential upwards.
WHat occurs first?
Atrial contraction(just before ventricular contraction)
What is the atrial kick?
Extra kick of blood by atria into ventricles at end of ventricular diastole.
What happens if ventricle contract before atrium contracts?
No kick.
What slows down conduction of AP?
AV node
Why does AV node slow conduction of AP?
Ensures sufficient time for atrial contraction before ventricular contraction.(allows no more than 200 beats per min thru to ventricles)
What is AF ?
Jelly atrium which beats 400-600 time per min.(if >150 ,not good)
WHat happens during ventricular depol. ?
Cells depolarize and become activated.
How does the wave spread?
Quickly from BASE to APEX and from ENDOcardial to EPIcardial regions.
What is the first thing to contract?
Septum.It becomes rigid and acts as a solid foundation for contraction of ventricular walls.
Heart consists of 2 layers of muscle and inside muscle contracts first,then outside.
What happens during ventr. repolarization?
Activated cells return to resting state.
How does the wave spread during ventr. repolarization?
Less quickly from apex to base and from EPIcardial to ENDOcardial regions.(longer AP in septum)
What does an ECG do?
Record surface electrical voltages from voltage differences generated within heart.
In an ECG,the magnitude of voltages depend on the mass of tissues involved(no. of cells)
True-greater in ventricles than in atria.
The direction of voltages is the sum of the depol. and repol. waves.