Karius: Cardiac Cycle and Normal ECG ibook notes Flashcards Preview

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Fast action potentials are found where

atrial and ventricular


Slow action potentials are found

in the SA and AV nodes


Fast action potential phase 0:

rapid upsweep (depolarization)

voltage gated Na channels open and the cell is rapidly depolarizing

same as skeletal muscle


Fast action potential phase 1:

occurs around +20 mV

Initial repolarization

sodium channels inactivate so no more sodium enters; voltage gated potassium channels open


Fast action potential phase 2:


"slow voltage gated calcium channels opening" AND "special voltage gated K channels closing"


Fast action potential phase 3:

Repolarization, Slow Ca channels closing and special K channels opening


Fast action potential phase 4:

resting potential sustained by high potassium conductance

around -85 mV


SA node and AV node AP: phase 4

resting membrane potential is NOT isotonic, gradually increases (depolarizes) until threshold value achieved and SA first; this is due to the funny Na voltage gated channels. (Na channels open during repolarization)

this is an intrinsic spontaneous event

AV node has same thing but phase 4 is much slower, normally doesnt reach threshhold value before being stimulated by an action potential originating in the SA node


SA node and AV node AP: phase 0

due to opening of slow Ca gates and closing of special K gates

same for AV node


SA node and AV node AP: phase 3

remember: no 1 or 2 phase, goes from 0 to 3


Normal EKG: P wave

atrial contraction


Normal EKG: QRS wave

ventricular contraction


Normal EKG: T wave

ventricular repolarization


PR interval

starts at beginning of P wave and ends at beginning of QRS complex

AV nodal delay time.

represents time it takes to pass from atria to the ventricles via the AV node: this is incorrect I believe


ST wave

begins at end of QRS, ends at beginning of T


QR interval:

begins with beginning of the QRS complex and ends at the end of the T wave, so it includes two waves

QRS and T wave

represents total time any ventricular myocite is depolarized


beginning of P wave and the cardiac cycle

both atria and ventricles are in diastole
all voltage gated channels are closed except for leaky K and Na/K ATPase

SA and AV nodes in P4, with funny Na channels operating (pre-potential)

AV has fewer funny channels so its pre-potential is slower to develop

Tricuspid and Bicuspid are open

Aortic and pulmonic are closed


pressure of left and right atrium during diastole

diastolic mmHG is usually 4 mmHg


pressure in left and right ventricles during diastole

0 mmHg

pressure in ventricle must be less than in atria for blood to flow


Pulmonary artery pressure diastole

15 mmHg


Aorta pressure diastole

80 mmHg


how will diastole pressure be effected if resistance in the arteries is high?

diastolic pressure will be higher


how will diastole pressure be effected if resistance in the arteries is low?

diastolic pressure will be lower


Jugular Vein: why is this sensitive to blood flow changes?

there are no valves between the atria and the veins

changes in atria; pressure will effect venous return


Atrial contraction: wave, pressure direction, direction of blood, and ventricular pressure

P wave
from atria into ventricles
ventricular pressure increases as well


Why doesnt the ventricle contract before the atria?

the AV has a slow ventricular depolarization to allow for blood to fill


What is the normal pressure of the ventricles at their height of contraction?

around 120 mmHg, on the left side


During the ___ wave the left ventricular pressure begins to increase.

P wave


During the QR phase, the left ventricle pressure

decreases for a moment and then increases,


the mitral valves open at _____ wave

the pinnacle of the R wave