Electrophysiology

Question 1

what is the resting membrane potential for the ventricular action potential

Answer 1

-90mV

Question 2

what creates a plateau on the ventricular conduction system

Answer 2

sustained period of depolarisation when there are equal influx and efflux of postivie and negative ions

Question 3

what are the L type calcium channels

Answer 3

those that are slow to open and slow to close

Question 4

when does potassium leave the cell

Answer 4

during action potential

Question 5

describe depolarisation of ventricles

Answer 5

sodium enters the cell to give 20mV potential
calcium channels contribute toward the end of the upstroke
sodium channels are inactivated quickly

Question 6

describe phase one of the ventricular action potential

Answer 6

small repolarisation because the sodium channels are inactivated but there are potassium ions leaving the cell

Question 7

describe phase two of ventricular action potential

Answer 7

the plateau - calcium ions are continuing to enter the cell at the same time as the potassium ions leaving which balances out the current to allow for sustained depolarisation

Question 8

describe phase three of ventricular action potential

Answer 8

calcium ions closed at the end phase two, but potassium ions are continuing to leave the cell, and there is repolarisation

Question 9

describe phase four of ventricular action potential

Answer 9

resting membrane potential

Question 10

what is the relative refractory period

Answer 10

the period near the end of action potential whereby if there is a strong stimulus it would be possible for there to be another action potential generated

Question 11

do the nodal cells of the heart need nerves to generate their action potential

Answer 11

no, they can spontaneously depolarise and generate action potentials without the help of the nervous system

Question 12

why can cardiac conduction cells generate their own action potentials

Answer 12

their resting potentials naturally drift toward the threshold to fire action potentials because their membrane is leaky

Question 13

describe upstroke in conducting cells

Answer 13

calcium ions enter the cell slowly, making upstroke slower and less steep than in the contractile cells

Question 14

describe phase 0 of the sino atrial node conduction

Answer 14

calcium ions enter the cell

Question 15

describe phase 3 of the sino atrial node conduction

Answer 15

calcium channels have closed, but potassium ions continue to leave the cell

Question 16

describe the funny current

Answer 16

the sino atrial node membrane is leaky and allows sodium to leak into the cell, which causes slow upstrake during phase four to allow for spontaneous depolarisation

Question 17

what causes spontaneous depolarisation in the sino atrial node

Answer 17

the funny current

Question 18

why does the sino atrial node set the rhthym rather than the other nodal cells

Answer 18

it has the fastest discharge rate of action potential so it sends the action potentials to the others before they have time to generate their own

Question 19

describe the effect of the nervous system on the cardiac conduction system

Answer 19

it does not initiate the conduction, but it can change the rate of it

Question 20

what are the five waves on an ECG

Answer 20

P
Q
R
S
T

Question 21

how can the waves above the baseline be described as

Answer 21

positive deflections

Question 22

what is the baseline of the ECG

Answer 22

isoelectric

Question 23

which waves are positive deflections

Answer 23

P R and T

Question 24

which waves are negative deflections

Answer 24

Q and S

Question 25

what is the P wave

Answer 25

atrial depolarisation, just before the contraction of the atria

Question 26

what is the QRS complex

Answer 26

ventricular depolarisation

Question 27

where can atrial repolarisation be found on the ECG

Answer 27

buried in the QRS complex

Question 28

what is the T wave

Answer 28

ventricular repolarisation

Question 29

what are the two segments found on an ECG

Answer 29

PQ and ST

Question 30

describe the PQ segment

Answer 30

end of atrial depolarisation to the start of ventricular depolarisation

Question 31

describe the ST segment

Answer 31

plateau of the ventricular action potential

Question 32

what is the J point

Answer 32

the junction between the end of the S wave and the beginning of the ST segment

Question 33

what is the PQ interval

Answer 33

the interval from the start of the P to the beginning of the Q wave. the start of atrial depolarisation to the onset of the ventricular depolarisation

Question 34

what is the QT interval

Answer 34

the onset of the Q wave to the end of the T wave

Question 35

what is the RR interval

Answer 35

one cycle to the next, and it used to calculate heart rate

Question 36

what is represented by the end of the T wave

Answer 36

the end of ventricular repolarisation

Question 37

how long is each small square on ECG paper

Answer 37

0.04 seconds

Question 38

how long is represented by larger boxes

Answer 38

0.2 seconds

Question 39

how many mV in every ten small boxes

Answer 39

1 mV

Question 40

what is the rate of the ECG paper

Answer 40

25mm recorded a second