Lecture 12 (Electrical activity of the heart)

Question 1

Describe the movement of heart beat through the heart? (4)

Answer 1

1. Initiated at sino-atrial node (pacemaker)
2. Conduction to atria and atrioventricular node.
   Then atrioventricular ring
3. Passage through bundle of His
4. Purkinje system distribution to ventricular muscle cells

Question 2

Where is heart beat imitated?
and what direction does it move?

Answer 2

Heart-beat initiated at sino-atrial node (which is pacemaker)
Spread from right to left, movement from atria to ventricles

Question 3

What are the 3 sub zones of the AV node? (3)

Answer 3

Atrial nodal transition section
Nodal area
Nodal ventricle transition section

Question 4

What is the speed of conduction like at the Sino-atrial node and AV node?

Answer 4

Slow (0.05m/s)

Question 5

Describe the sub nodal conduction in the heart? (6)

Answer 5

1) Depolarise atria
2) Depolarise septum left to right
3) Depolarise anteroseptal region of the myocardium towards the apex
4) The ventricles are now depolarised
5) Depolarise posterior portion of base of the left ventricle
6) Depolarise bulk of ventricular myocardium. from endocardium to pericardium

Question 6

How fast is sub-nodal conduction?

Answer 6

Fast via His (1m/s)
Purkinje fibres (4m/s)
ventricular muscle (1m/s)

Question 7

What are the types of cardiac AP? (5)

Answer 7

-SA Node
-Atrial muscle
-AV Node
-Purkinje fibres
-Ventricular muscle

Question 8

What is the difference in length of AP in cardiac and skeletal muscle?

Answer 8

Longer Aps in cardiac muscle vs skeletal muscle

Question 9

Which cells act as pacemakers? (3)

Answer 9

Sa node
If doesn’t work then Av node and Purkinje fibres can act as pacemakers

Question 10

What is pacemaker Ap regulated by? (3)

Answer 10

Regulated by innervation, temp, other pacemakers

Question 11

What does Sympathetic system do in regards to pacemaker cells? (3)

Answer 11

-Sympathetic system increase firing rate of pacemaker cells
-Regulates size of funny current through cyclic amp which is regulated by noradrenaline
-This means a faster depolarization to threshold

Question 12

What do vagal fibres do?

Answer 12

Control hyper-polarisation & decreased pre-potential slope

Question 13

What do calcium clock oscillations do?

Answer 13

(rhythmic alterations of SR Ca2+ release – actn NCX - depolarisation)

Question 14

When can cardiac muscle fire AP?

Answer 14

When triggered to do so my myocyte next to them

Question 15

Describe Cardiac muscle AP? (4)

Answer 15

-No automaticity
-Long plateau phase
-Propagated and prolonged action potential
-Fast depolarisation and overshoot

Question 16

Describe the ion channels in cardia muscle AP?

Answer 16

1) Voltage gated Na+ channels open
2) Na+ inflow depolarises membrane and more channels open
3) Na+ channels close when depolarised
4) Ca2+ enters through slow Ca2+ channels and prolongs depolarisation (creates plateau), some K+ leak
5) Ca2+ channels close and Ca2+ moves out, K+ channels open, membrane returns to resting potential