Excitation across the heart Flashcards
Where is heart conduction initiated?
In pacemaker cells of SA node of the atrium - AP spread across the atria via gap junctions of intercalated discs of atrial myocytes
What does heart conduction stimulate?
AV node, passing along Bundle of His and spreads across purkinje system to apex of ventricles triggering contraction to arteries
What are 5 steps to conduction system in the heart?
SA node AV node Bundle of His Right and Left bundle branches Purkinje fibres
What does SA pacemaker cells have a RMP of?
-60mV
What is the RMP?
electrical potential difference that exist across the cell membrane under resting conditions
What is the funny current?
Membrane has a leakage curren in sodium
What raises the RMP?
steady rise inhibits efflux of potassium ions further raising RMP
What is a steady raising RMP called?
-40mV - this is threshold and triggers the pacemaker cell AP
Where are the SA pacemaker cells positioned?
Right atrial wall inferior to the opening of the superior vena cava
At what threshold does voltage gated calcium channels open?
-40mV triggers opening of slow membrane L-type which slowly depolarises the cells to +10mV
What does depolarising of pacemaker cells lead to?
followed by repolarisation mediated by opening of potassium channel and activates sodium potassium pump for exchange
What are the cardiac myocyte AP phases?
4 main - depolarisation, plateau, repolarisation phase
What happens in the depolarisation phase?
cardiac myocytes RMP of -90mV when voltage sodium channels open cell depolarises to +20 mv - then sodium channel inactivated for a while
What happens in the Plateau phase?
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
What happens in the repolarisation phase?
potassium channels open and pump is activated and the cell repolarises
Where is the AV node and what does it conduct?
Anterior to opening of coronary sinus and only point of electrical contact between atria and ventricles firing rate of 40-60 potentials
Where is bundle of his and what does it conduct?
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
Where is the Purkinje fibres?
Large diameter extensions of bundle of his extend from apex of heart into ventricular walls
what machine measures cardiac potentials as they propagate through heart (AP produced by all heart muscle cells)?
ECG or EKG - electrocardiagram - Einhovens triangle, 10 electrodes for 12 lead ecg
What are the 3 recognisable waves in an ECG?
P - depolarisation of atria
QRS - depolarisation of ventricles
T - repolarisation of ventricles
What are the 3 intervals in ECG?
P-Q - conduction time between SA node and ventricular depolarisation
S-T - ventricular cells depolarised in plateua
Q-T - ventricular depolarisation to repolarisation
What is the correlation of ECG waves and Systole?
Cardiac AP - p wave atrial contraction AP enters AV - QRS Contraction of ventricles S-T Repolarisation - T wave Diastole
What is a Junctional rhythm?
Non-functional SA node,absence of P wave, paced by AV node
What is a heart block?
some P waves not conducted through av, 2 P waves
What is ventricular fibrillation?
Chaotic, irregular trace, acute heart attacks, ventricles no long pump blood
