Cardiac Physiology and ECG's Flashcards
what is depolarisation
the process by which the electrical charge of a cell becomes more positive (often the contraction phase)
what is repolarisation
the process by which the electrical charge of a cell becomes more negative, generally returning to it’s resting membrane potential (often the relaxation phase)
what are the four chambers of the heart
right atrium, left atrium, right ventricle, left ventricle
what is automaticity?
the property of a cardiac cell to produce it’s own action potential without relying on surrounding cells
where is the sinoatrial node
top right section of the right atrium
where is the atrioventricular node
located between the atrium and ventricles
what are internodal tracts?
connect the SA and AV nodes
what is an important role of the AV node?
to delay depolarisation between the atria and ventricles so that they are not contracting at the same time, allowing for adequate ventricular filling
explain the process of a cardiac myocyte action potential
positive ions leak through gap junctions to cell > increase membrane voltage from -90 to -70 (threshold potential) > fast sodium channels open > influx of positively charged Na ions > rise in voltage > slow calcium channels open > peaks at around +30 > potassium channels open/ Na channels close > efflux of K+ decreases charge of cell > influx of calcium and efflux of potassium causes plateau phase > calcium channels close and efflux of K+ causes depolarisation of cell
explain the process of a cardiac pacemaker action potential
RMP of pacemaker is roughly -60 > spontaneously increases to -40 (threshold potential) > calcium channels open > influx of positively charged calcium ions > cell depolarises until roughly +10 > calcium channels close and potassium channels open > efflux of positively charged potassium ions > cell voltage returns to -60 mV
*cell may hyper polarise and then return to normal via sodium/potassium pump
When is the absolute refractory period and relative refractory period and what do they mean?
what does the p-wave represent on an ECG?
atrial depolarisation
what does the p-r interval represent on an ECG?
begining of atrial contraction to the begining of ventricular contraction / the time taken for an impulse to reach the ventricles from the SA node
what does the PR segment represent on an ECG?
it signifies AV nodal delay, goes from the end of the p-wave (end of atrial contraction) to the begining of the QRS complex (ventricular contraction)
what does the QRS complex represent on an ECG?
ventricular depolarisation
