Cardiac Cycle and Electrical Activity Flashcards
cardiac cycle
•period of time that begins with contraction (systole) of the atria and ends with ventricular relaxation (diastole)
P wave
•depolarization of the atria •contraction of the atria
QRS complex
•depolarization of the ventricles •contraction of the ventricles
T wave
•repolarization of the ventricles
EDV
•end diastolic volume •volume of blood in the ventricles at the end of atrial systole and before ventricular contraction
S1
•mitral and tricuspid valves closing •”LUB”
S2
•pulmonary and aortic valves closing •”DUB”
atrioventricular valves
•tricuspid •mitral (bicuspid)
semilunar valves
•aortic •pulmonary
SV
•stroke volume •amount of blood pumped by the ventricles
ESV
•volume of blood remaining in the ventricle following ventricular contraction
autorhythmicity
•the ability to initiate an electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger the contractile mechanism
two types of cardiac cells
•myocardial contractile cells •myocardial conducting cells
myocardial contractile cells
•constitute the bulk (99%) of the cells in the atria and ventricles •conduct impulses and are responsible for contractions that pump blood through the body
myocardial conducting cells
•1% of the cells •form the conduction system of the heart •except for Purkinje cells. they are generally much smaller than the contractile cells and have few of the myofibrils or filaments needed for contraction •initiate and propagate the action potential that travels throughout the heart and triggers the contractions that propel the blood •pacemaker cells
4 major areas of pacemaker cells
•sinoatrial node (SA node) •atrioventricular node (AV node) •the bundle of HIS (right and left branches) •Purkinje fibers
SA node
•near superior and posterior walls of right atrium •highest inherent rate of depolarization, known as the pacemaker of the heart, initiates sinus rhythm •without nervous or endocrine control, would initiate a heart impulse approx. 80-100/ min
overdrive suppression
•the SA node depolarizes faster than the other pacemaker cells, and the SA node forces them to go
AV node
•inferior portion of the right atrium within the atrioventricular septum • the septum prevents the impulse from going straight to the ventricles, allowing for the AV nodal delay - allows atrial cardiomyocytes to complete their contraction before transmitting the impulse to the ventricles
bundle of His
•interventricular septum •divides into two branches - right and left (two fascicles, larger)
Purkinje fibers
•spread the impulse to the myocardial contractile cells in the ventricles
action potential at the SA node
•Phase 0: upstroke (depolarization) result of an increase in Ca++ conductance and an inward Ca++ current, T type Ca++ channel •Phase 1-2: not found in autorhythmic cells •Phase 3: repolarization in the SA node due to an increase in K+ conductance, K+ leaves the cell •Phase 4: spontaneous depolarization, K+ stops leaving and a “Funny” inward channel opens due to repolarization (can carry any + charged ion into the cell, but tends to move Na+) – ensures that each action potential in the SA node will be followed by another
action potential of a ventricular cardiac myocyte
•Phase 0: fast depolarization due to sudden increase in permeability to Na+, closes quickly due to change in membrane potential •Phase 1: short, rapid repolarization that is caused by the combination of the Na+ channels inactivating and an outward K+ current •Phase 2: plateau, long, relatively stable, depolarized membrane potential due to an increase in Ca++ inward (different than in nodal cells!) L type channels, outward K+ channel to balance Ca++ current, net current is 0 •Phase 3: repolarization due to decrease in Ca++ conductance and increase in K+ conductance •Phase 4: stable resting potential, closure of all channels, no action potential until a signal comes in from the nodal cells
Absolute Refractory Period
•cannot be another depolarization
