Excitation across the heart

Question 1

Where is heart conduction initiated?

Answer 1

In pacemaker cells of SA node of the atrium - AP spread across the atria via gap junctions of intercalated discs of atrial myocytes

Question 2

What does heart conduction stimulate?

Answer 2

AV node, passing along Bundle of His and spreads across purkinje system to apex of ventricles triggering contraction to arteries

Question 3

What are 5 steps to conduction system in the heart?

Answer 3

SA node
AV node
Bundle of His
Right and Left bundle branches
Purkinje fibres

Question 4

What does SA pacemaker cells have a RMP of?

Answer 4

-60mV

Question 5

What is the RMP?

Answer 5

electrical potential difference that exist across the cell membrane under resting conditions

Question 6

What is the funny current?

Answer 6

Membrane has a leakage curren in sodium

Question 7

What raises the RMP?

Answer 7

steady rise inhibits efflux of potassium ions further raising RMP

Question 8

What is a steady raising RMP called?

Answer 8

-40mV - this is threshold and triggers the pacemaker cell AP

Question 9

Where are the SA pacemaker cells positioned?

Answer 9

Right atrial wall inferior to the opening of the superior vena cava

Question 10

At what threshold does voltage gated calcium channels open?

Answer 10

-40mV triggers opening of slow membrane L-type which slowly depolarises the cells to +10mV

Question 11

What does depolarising of pacemaker cells lead to?

Answer 11

followed by repolarisation mediated by opening of potassium channel and activates sodium potassium pump for exchange

Question 12

What are the cardiac myocyte AP phases?

Answer 12

4 main - depolarisation, plateau, repolarisation phase

Question 13

What happens in the depolarisation phase?

Answer 13

cardiac myocytes RMP of -90mV when voltage sodium channels open cell depolarises to +20 mv - then sodium channel inactivated for a while

Question 14

What happens in the Plateau phase?

Answer 14

sodium current triggers opening of slow membrane calcium ion channels allowing small influx of calcium into cells - triggers calcium from SR uses 250ms decreased permeability to potassium

Question 15

What happens in the repolarisation phase?

Answer 15

potassium channels open and pump is activated and the cell repolarises

Question 16

Where is the AV node and what does it conduct?

Answer 16

Anterior to opening of coronary sinus and only point of electrical contact between atria and ventricles firing rate of 40-60 potentials

Question 17

Where is bundle of his and what does it conduct?

Answer 17

extends from av node down to ventricular septum where it divides into 2 bunds left and right - extend to apex of heart and firing rate of 20-36 potentials

Question 18

Where is the Purkinje fibres?

Answer 18

Large diameter extensions of bundle of his extend from apex of heart into ventricular walls

Question 19

what machine measures cardiac potentials as they propagate through heart (AP produced by all heart muscle cells)?

Answer 19

ECG or EKG - electrocardiagram - Einhovens triangle, 10 electrodes for 12 lead ecg

Question 20

What are the 3 recognisable waves in an ECG?

Answer 20

P - depolarisation of atria
QRS - depolarisation of ventricles
T - repolarisation of ventricles

Question 21

What are the 3 intervals in ECG?

Answer 21

P-Q - conduction time between SA node and ventricular depolarisation
S-T - ventricular cells depolarised in plateua
Q-T - ventricular depolarisation to repolarisation

Question 22

What is the correlation of ECG waves and Systole?

Answer 22

Cardiac AP - p wave
atrial contraction
AP enters AV - QRS
Contraction of ventricles S-T
Repolarisation - T wave
Diastole

Question 23

What is a Junctional rhythm?

Answer 23

Non-functional SA node,absence of P wave, paced by AV node

Question 24

What is a heart block?

Answer 24

some P waves not conducted through av, 2 P waves

Question 25

What is ventricular fibrillation?

Answer 25

Chaotic, irregular trace, acute heart attacks, ventricles no long pump blood