Electrical Activity Of Heart

Question 1

What is a functional syncytium?

Answer 1

When the cardiac muscle cells are independent of each other but still work together.
They are connected electrically by gap junctions and physically by desmosomes.
Together these form intercalated discs

Question 2

How long is the cardiac action potential?

Answer 2

200-250 milliseconds

Question 3

Can cardiac muscle exhibit tetanic contraction?

Answer 3

No

Question 4

Is contractile strength variable in cardiac muscle?

Answer 4

Yes, calcium does not saturate the troponin so regulation of its release can be used to vary strength of contraction, unlike in skeletal muscle.

Question 5

What is happening at phase 4 of the cardiac action potential?

Answer 5

K channel open, no net flow

Question 6

What happens at phase 0 of cardiac action potential?

Answer 6

Rapid depolarisation with Na flowing in and K out.

Question 7

What happens at phase 1 of cardiac action potential?

Answer 7

Na Channel shuts, K Channel open

Question 8

What happens at phase 2 of the cardiac action potential?

Answer 8

Calcium flows in, K closes
(Plateau)

Question 9

What happens at phase 3 of the cardiac action potential?

Answer 9

Calcium channel closes while K flows out (repolarisation)

Question 10

What happens in the pacemaker action potential?

Answer 10

Increase in calcium (depolarisation)

Before that: gradual decrease in Pk
Early increase in PNa
Late increase in PCa2+

Question 11

How long should the PR interval be?

Answer 11

0.2 seconds or less

Question 12

What does a long PR interval suggest?

Answer 12

1st degree heart block

Question 13

What does (mobitz type 1) 2nd degree heart block look like on an ECG?

Answer 13

Increasing PR interval followed by dropped QRS complex.

Question 14

What is 3rd degree heart block?

Answer 14

No relationship between P wave and QRS complex.

Question 15

How long should ECG segments be?

Answer 15

PR interval, 0.12-0.2 s
QRS complex, 0.12 s
QT interval, 0.42 s