ECG

Question 1

What is the SAN?

Answer 1

• Autorythmic cells
• Initiate & conduct AP
• Slowly ‘drift’ to threshold

Question 2

How does the SAN node produce its action potential?

Answer 2

With the SAN there is no resting potential.
* Sodium slowly leaks out via the funny channels until depolarisation
* As you approach the threshold pot Ca2+ goes in via the transient-type channels.
* Once the threshold has been reached these channels close. And the long lasting channels open.
* At the peak of the potential the the L-type channel close and the K+ channel open letting potassium out. Which allows for quick repolarisation.

Question 3

Describe how cardiomyocytes carry an AP?

Answer 3

• Rapid influx of Na in which causes rapid depolarisation
• Potassium channels open briefly to cause repolarisation.
• Plateau phase there’s Ca2+ slowly entering the cell
• At the end of the plateau theres rapid repolarisation where the K+ ions are pumped out.

Question 4

What occurs during the P-Wave?

Answer 4

Depolarisation of atria in response to SA node triggering.

Question 5

What occurs during the PR interval?

Answer 5

Delay of AV node to allow filling of ventricles.

Question 6

What occurs during the QRS complex?

Answer 6

Depolarisation of the ventricles, triggers main pumping contractions.

Question 7

What is the ST segment?

Answer 7

Beginning of the ventricle repolarisation, should be flat.