Cardiac Cycle and Electrical Activity

Question 1

cardiac cycle

Answer 1

•period of time that begins with contraction (systole) of the atria and ends with ventricular relaxation (diastole)

Question 2

P wave

Answer 2

•depolarization of the atria •contraction of the atria

Question 3

QRS complex

Answer 3

•depolarization of the ventricles •contraction of the ventricles

Question 4

T wave

Answer 4

•repolarization of the ventricles

Question 5

EDV

Answer 5

•end diastolic volume •volume of blood in the ventricles at the end of atrial systole and before ventricular contraction

Question 6

S1

Answer 6

•mitral and tricuspid valves closing •”LUB”

Question 7

S2

Answer 7

•pulmonary and aortic valves closing •”DUB”

Question 8

atrioventricular valves

Answer 8

•tricuspid •mitral (bicuspid)

Question 9

semilunar valves

Answer 9

•aortic •pulmonary

Question 10

SV

Answer 10

•stroke volume •amount of blood pumped by the ventricles

Question 11

ESV

Answer 11

•volume of blood remaining in the ventricle following ventricular contraction

Question 12

autorhythmicity

Answer 12

•the ability to initiate an electrical potential at a fixed rate that spreads rapidly from cell to cell to trigger the contractile mechanism

Question 13

two types of cardiac cells

Answer 13

•myocardial contractile cells •myocardial conducting cells

Question 14

myocardial contractile cells

Answer 14

•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

Question 15

myocardial conducting cells

Answer 15

•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

Question 16

4 major areas of pacemaker cells

Answer 16

•sinoatrial node (SA node) •atrioventricular node (AV node) •the bundle of HIS (right and left branches) •Purkinje fibers

Question 17

SA node

Answer 17

•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

Question 18

overdrive suppression

Answer 18

•the SA node depolarizes faster than the other pacemaker cells, and the SA node forces them to go

Question 19

AV node

Answer 19

•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

Question 20

bundle of His

Answer 20

•interventricular septum •divides into two branches - right and left (two fascicles, larger)

Question 21

Purkinje fibers

Answer 21

•spread the impulse to the myocardial contractile cells in the ventricles

Question 22

action potential at the SA node

Answer 22

•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

Question 23

action potential of a ventricular cardiac myocyte

Answer 23

•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

Question 24

Absolute Refractory Period

Answer 24

•cannot be another depolarization

Question 25

Effective Refractory Period

Answer 25

•period of time that’s very hard to depolarize, but might allow non-propagated depolarization (by altering ion movement in or out of the cell)

Question 26

Relative Refractory Period

Answer 26

•when the cell can depolarize again, but it takes a larger than normal stimulus

Question 27

Supranormal Period

Answer 27

•a very short time when the cell is hyperexcitable (a smaller than normal stimulus can cause depolarization)