Electrical System

Question 1

‘Intracellular charge is more negative than outside the cell’ - describes what potential state?

Answer 1

Resting membrane potential

Question 2

‘Intracellular charge is less negative than outside the cell’ - describes what potential state?

Answer 2

Depolarisation

Question 3

‘Ion exchange causing intracellular charge to reduce’ -describes what potential state?

Answer 3

Repolarisation

Question 4

Describe phase 0 of AP (Depolarisation)

Answer 4

Rapid Sodium influx
Slow Calcium influx

Intracellular charge changes from - to + and triggers myocardial contraction

Question 5

Describe phase 1 of AP

Answer 5

Sodium influx blocked
Slow Calcium influx continues

Intracellular charge becomes more negative

Question 6

Describe phase 2 of AP (plateau phase)

Answer 6

Sodium influx still blocked
Slow Calcium influx continues
Potassium efflux starts

Calcium influx is equal to Potassium efflux

Cell supersaturated with IONS - No Stim possible regardless of strength

Question 7

Describe phase 3 of AP (Rapid repolarisation)

Answer 7

Sodium influx blocked
Calcium influx blocked
Rapid Potassium efflux

These conditions lower intracellular voltage. Stim possible but only with high voltage

Question 8

Described phase 4 of AP (Resting phase)

Answer 8

Sodium efflux via pump
Potassium influx via pump

Concentrations returned to pre-depolarisation levels. Ready for Stim.

Question 9

What is the normal range for the SA node at rest

Answer 9

60-100 bpm

Question 10

Define automaticity

Answer 10

Ability to initiate an impulse

Question 11

Define excitability

Answer 11

Ability to respond to an impulse

Question 12

Define conductivity

Answer 12

Ability to transmit an impulse

Question 13

Where is the SA node located?

Answer 13

In the Right Atrium where the SVC enters

Question 14

What are the 3 internodal tracts in the RA?

Answer 14

Anterior
Middle
Posterior

Question 15

How does the impulse travel from the RA to the LA

Answer 15

Bachmann’s bundle - near simultaneous contraction

Question 16

Where is the AV node located?

Answer 16

Inferior RA near the Cs Os

Question 17

How long does the AV node delay the impulse?

Answer 17

0.04ms

Question 18

Why does the AV node delay the impulse?

Answer 18

To allow ventricular filling from atrial contraction

Question 19

Describe the bundle of HIS

Answer 19

Transports the impulse from the AV node. Bifurcates into the left and right bundle branches

Question 20

What is the firing rate of the bundle of HIS?

Answer 20

40-60bpm

Question 21

Which bundle branch is thicker and why?

Answer 21

The left due to thicker LV wall

Question 22

Which bundle branch is faster and why?

Answer 22

The left is faster as more muscle mass must be stimulated in the same amount of time, otherwise contraction between LV/RV will not be synchronous.

Question 23

Describe Purkinje fibres

Answer 23

Final part of the conduction system. They deliver the impulse from the endocardium to the ventricular myocardium and epicardium.

Question 24

What is the pacemaker speed of Purkinje Fibres?

Answer 24

15-40bpm