Lecture 9

Question 1

What is a cardiac conduction cell?

Answer 1

Has a pale and striated appearance with low actin and myosin

Question 2

How much of all cardiac cells do the conduction cells make up?

Answer 2

1%

Question 3

What is a cardiac contractile cell?

Answer 3

Had a striated appearance with high actin and mysin

Question 4

How much of all cardiac cells do the contractile cells make up?

Answer 4

99%

Question 5

Where does depolarisation begin?

Answer 5

At the sinoatrial node (SAN)

Question 6

How does depolarisation spread?

Answer 6

Through the gap junctions of the intercalated disks

Question 7

What is a gap junction?

Answer 7

Pores within the sides of the cells that has low ionic current resistance

Question 8

In what direction does depolarisation spread?

Answer 8

In all directions because it can spread through both cardiac and contractile cells

Question 9

What is a functional syncytium?

Answer 9

Many things behaving as one functional unit

Question 10

What is the pacemaker of the heart?

Answer 10

The sinoatrial node

Question 11

Where is the SA node located?

Answer 11

In the right atrium

Question 12

Once an electrical signal has been conducted in the SA node, where does it spread to first?

Answer 12

The left atrium via the interatrial bundle pathway of conduction cells

Question 13

Why does the electrical signal flow between atria first?

Answer 13

To allow simultaneous contraction of the two atria

Question 14

How does an electrical signal get to the AV node?

Answer 14

Via the internodal bundles

Question 15

Why does the electrical signal pause at the AV node?

Answer 15

To allow the atria to stop contracting before the ventricles contract

Question 16

Where does an electrical signal go after the AV node?

Answer 16

To the Purkinje fibres via the bundle branches

Question 17

Why does the electrical signal travel to the apex of the heart first?

Answer 17

For the highest efficiency contraction of the ventricles to push as much blood out of the heart as possible

Question 18

What is quiescence?

Answer 18

When there is no electrical signal, the heart is fully repolarised

Question 19

What are the steps of relaxation, depolarisation and repolarisation during heart contraction?

Answer 19

Initially at quiescence (all 4 chambers relaxed), excitation spreads from SA node, atria depolarise, atria repolarise and AV node sends excitation to ventricles, ventricles depolarise and contract, ventricles repolarise, heart fully relaxes again

Question 20

What does an ECG detect?

Answer 20

Changes in polarisation state within the heart

Question 21

What are the features of an ECG trace?

Answer 21

The P wave, QRS complex, T wave

Question 22

What is the P wave?

Answer 22

Detection of depolarisation in the atria

Question 23

What is the QRS complex?

Answer 23

Two things happening at once. Atria repolarising while ventricles depolarise

Question 24

What is the T wave?

Answer 24

Detection of the repolarisation in the ventricles

Question 25

What is the cause of the gap between the P wave and QRS complex?

Answer 25

The delay between atrial and ventricular depolarisation, caused by the AV node

Question 26

Why is the QRS complex the largest wave on the ECG trace?

Answer 26

The ventricles contain the greatest amount of muscle so create a greater depolarisation

Question 27

What part of an ECG trace is the lubb heart sound associated with?

Answer 27

The S wave - end of the QRS complex - ventricular depolarisation complete and isovolumetric phase begins so the atrioventricular valves close

Question 28

What part of an ECG trace is the dupp heart sound associated with?

Answer 28

At the end of the T wave - ventricular repolarisation complete and the semilunar valves close