Electrical Physiology

Question 1

resting muscle cell: what can or can’t move

Answer 1

only K+ can easily enter cell; all other ions and protiens and DNA can’t

Question 2

concentration gradients for Ca, Na, K

Answer 2

lots of Ca and Na outside; lots of K inside

Question 3

myocardial AP: phase 0

Answer 3

rapid upstroke: cell voltage rises above threshold = Na channels opening, Na influx = increase in voltage

Question 4

myocardial AP: phase 1

Answer 4

brief repolarization: small drop in voltage caused by transient K+ channel opening = outward current

Question 5

myocardial AP: phase 2

Answer 5

plateau phase: balanced K+ out with Ca+ in

Question 6

myocardial AP: phase 3

Answer 6

repolarization: K+ efflux to restore negative membrane voltage; Ca channels have closed

Question 7

myocardial AP: phase 4

Answer 7

slow depolarization: slow inward leak of Na (maybe Ca) –> eventually will trigger next systole

Question 8

basis for ECG:

Answer 8

difference in voltage when part of heart de/repolarizes before another –> drives current through wires attached to body = ECG signal

Question 9

ECG: amplitude of deflection varies with?

Answer 9

number of cells different, and distance from electrode (most signal comes from closest part)

Question 10

ECG positive/negative conventions

Answer 10

wave of positive cell depolarization going towards electrode (or negative going away) = positive deflection. positive going away, or negative going towards electrode = negative deflection

Question 11

ECG: perpendicular depol? if all cells are - or +?

Answer 11

no deflection

Question 12

ECG: positive signal going towards electrode, when is is max?

Answer 12

maximum signal when half muscle is positive, half is negative = peak of spike –> then it starts to go down

Question 13

direction of de and repolarization and what ECG looks like

Answer 13

depol: from inside to out = fast spike of positive deflection. repol = outside to in so a slow broad positive deflection

Question 14

2 main groups of electrodes/leads

Answer 14

6 limb leads and 6 chest leads

Question 15

Einthoven’s triangles: what are the three leads?

Answer 15

1: RA to LA. 2: RA to LL. 3: LA to LL. (RL = grounding electrode)

Question 16

vector of leads: what sums to what?

Answer 16

I + III = II (right arm to left arm plus left arm to left leg = right arm to left leg)

Question 17

what is assumed to be the origin of all electrical leads?

Answer 17

center of heart

Question 18

three augmented leads?

Answer 18

aVF straight down. aVL to the left and up. aVR to the right and up.

Question 19

what angles are the 6 leads at?

Answer 19

I at 0. II at 60. aVF 90. III 120. aVR -150. aVL -30.

Question 20

placement of precordial leads

Answer 20

V1 right 4 IC. V2 left. 3 down and to the left. 4 down and to the left; under nipple. 5 to the left. 6 to the left; near anterior axillary line.