Electrical activity of the heart Flashcards
Where is action potential generated?
The SA node which sits on the rights atrium
Why is it the SA node that drives heart rate?
The SA node depolarises fastest = generates and AP quicker than anywhere else in the heart.
What happens after SA depolarisation?
The atria depolarises, we get calcium influx and the atria contracts and pushes blood into the relaxed ventricle.
Why is there a delay between atria and ventricular depolarisation?
The AV node - it delays ventricular depolarisation to allow it time to be filled.
What happens after the AV delays the AP?
The AP travels down the septum and into the ventricle. The ventricle depolarises and contracts.
What happens to the atria while the ventricle contracts/depolarises?
The atria re polarises.
What is the P wave on an ECG?
Atrial depolarisation
What is the gap between P and Q on an ECG?
the atria contracting. The delay is because of the AV node = ventricle is being filled and stretched to improve efficiency.
What is the QRS wave on an ECG?
Ventricular depolarisation
What is the gap between S and T on an ECG?
the ventricle contracting
What is the T wave on an ECG?
Ventricle re polarisation
At rest, are the Na channels open or closed and is the voltage of the membrane -ve or +ve?
Closed and -ve
How does depolarisation happen?
A stimulus will cause the membrane to become more +ve = the Na+ channels will open for a m/s. In this time, due to high conc gradient, Na will flood in and drive the membrane potential = membrane will become positive.
What is the refractory period?
Once the sodium channels have opened they become inactive (can’t generate a second AP until they are exposed to a -ve charge
How does the membrane return to its -ve resting state?
K+ channels open and leave the cells making the membrane more -ve
