Electrical activity of the heart

Question 1

Which channels are responsible for the entry of extracellular Ca into the cell following depolarisation through the t-tubules?

Answer 1

L-type voltage gated calcium channels

Question 2

What detects an increase in intracellular calcium to initiate the release of calcium from the sarcoplasmic reticulum?

Answer 2

Ryanodine receptors

Question 3

How does calcium allow contraction of muscles?

Answer 3

Binds to troponin C, which removes tropomyosin from the actin binding site on myosin, allowing the head to bind actin

Question 4

How do intracellular calcium levels return to normal?

Answer 4

ATPase pump on SR/ER
Ejected from cell via Na-Ca exchanger
Plasma membrane calcium ATPase
Taken up by mitochondria

Question 5

What enzyme acts as a “brake” for the ATPase?

Answer 5

Phospholamban

Question 6

What structures are vital for the cardiac muscles to act as a “functional syncytium”?

Answer 6

Intercalated discs, made up of gap junctions and desmosomes so cardiac muscle cells are linked electrically and physically

Question 7

How long is a cardiac muscle action potential?

Answer 7

250msec

Question 8

How long is a skeletal muscle action potential?

Answer 8

2msec

Question 9

What is another name for the pacemaker potential?

Answer 9

Diastolic depolarisation, as the pacemaker potential represents the non-contracting time between heart beats during diastole

Question 10

What do cardiac glycosides do to electrical activity?

Answer 10

Increase calcium release, increasing the force of muscle contraction

Question 11

Give an example of an cardiac glycoside

Answer 11

Digoxin

Question 12

What affect does temperature have on electrical activity of the heart?

Answer 12

Increases ~10 beats per min per degree difference

Question 13

What is responsible for the early increase in Na in the pacemaker potential?

Answer 13

PF, funny current, opens Na upon repolarisation to allow pacemaking

Question 14

What affect does hyperkalaemia have on electrical activity?

Answer 14

Fibrillation and heart block

Question 15

What affect does hypokalaemia have on electrical activity?

Answer 15

Fibrillation and heart block (anomalous)

Question 16

What affect does hypercalcaemia have on electrical activity?

Answer 16

Increased HR and force of contraction

Question 17

What affect does hypocalcaemia have on electrical activity?

Answer 17

Descreased HR and force of contraction

Question 18

What speed are the electrical impulses in the SA node?

Answer 18

0.5m/sec

Question 19

What is the function of the annulus fibrosus?

Answer 19

Non-conducting, prevent the exit of electrical currents except at the AV nodes

Question 20

What speed are the electrical impulses in the AV node?

Answer 20

0.05m/sec (delayed to allow complete emptying of the atria before ventricle contracts)

Question 21

What speed are the electrical impulses in the bundle of His?

Answer 21

5m/sec (rapid for ventricular depolarisation)

Question 22

What does the P wave correspond to in the cardiac cycle?

Answer 22

Atrial depolarisation

Question 23

What does the QRS complex correspond to in the cardiac cycle?

Answer 23

Ventricular depolarisation

Question 24

What does the T wave correspond to in the cardiac cycle?

Answer 24

Ventricular repolarisation

Question 25

What are some common causes of heart block?

Answer 25

Coronary heart disease
Cardiomyopathy
Fibrosis of conducting system (particularly in elderly)

Question 26

Whats the most common type of arrhythmia?

Answer 26

Atrial fibrillation (no P waves, only f waves, fine oscillations)

Question 27

What % of those over 65yo have atrial fibrillation?

Answer 27

5-10%

Question 28

Which arrhythmia has the characteristic “sawtooth” appearance on ECGs?

Answer 28

Atrial flutter, F waves

Question 29

What causes atrial flutter?

Answer 29

IHD
Cardiomyopathy
Atrial septal defects

Question 30

Describe ventricular tachyarrhythmia

Answer 30

Ectopic electrical activity is not conducted to ventricles through normal conducting system, thus the QRS complexes are widened with a bizarre configuration