Question

Does an ECG tracing give us specific information about the change in membrane potential for the cardiomyocytes? Why not? ( Answer yes/no and then provide explanation based on what you know about the different waves/complexes)

Answer 1

ANSWER IS YES

Electrocardiography is the process of producing an electrocardiogram, a graph of voltage versus time – of the electrical activity of the heart .using electrodes placed on the skin. These electrodes detect the small electrical changes that are a consequence of cardiac muscle depolarization followed by repolarization during each cardiac cycle (heartbeat).

There are three main components to an ECG:

P wave,

The P wave represents

depolarization of the atria. Atrial depolarization spreads from the SA node towards the AV node, and from the right atrium to the left atrium.

QRS complex, which represents the depolarization of the ventricles

T wave, which represents the repolarization of the ventricles

P-R interval is the inetrval between the onset of p wave to the onset of QRS complex.In terms signal that means the time taken for the impulse to pass from the SAnode to atrium then into AV node then upto the upper part of Bundle of His.

SA node action potential has 4 phase

phase 1 is called the pacemaker potential it is due to the funny current (Na+) , T typre ca channel, transient outward potassium channel

phase 2 is depolarisation due to the opening of L type calcium channel

phase 3 is the repolarisation due to transient outward potassium channel

Ventricular action potential

phase 0 - resting membrane potential to peak action potential, it is by the opening of Na+ channel

phase 1 - is early repolarisation due to the transient outward k+ channel

phase 2 - plateau phase : due to the balance between L type calcium channel and delayed rectifying k+ channel

phase 3 - late repolarisation , due to the closure of L type ca+ channel and opening of delayed rectifying k+ channel