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Flashcards in Electrical System Deck (24)
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1
Q

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

A

Resting membrane potential

2
Q

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

A

Depolarisation

3
Q

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

A

Repolarisation

4
Q

Describe phase 0 of AP (Depolarisation)

A

Rapid Sodium influx
Slow Calcium influx

Intracellular charge changes from - to + and triggers myocardial contraction

5
Q

Describe phase 1 of AP

A

Sodium influx blocked
Slow Calcium influx continues

Intracellular charge becomes more negative

6
Q

Describe phase 2 of AP (plateau phase)

A

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

7
Q

Describe phase 3 of AP (Rapid repolarisation)

A

Sodium influx blocked
Calcium influx blocked
Rapid Potassium efflux

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

8
Q

Described phase 4 of AP (Resting phase)

A

Sodium efflux via pump
Potassium influx via pump

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

9
Q

What is the normal range for the SA node at rest

A

60-100 bpm

10
Q

Define automaticity

A

Ability to initiate an impulse

11
Q

Define excitability

A

Ability to respond to an impulse

12
Q

Define conductivity

A

Ability to transmit an impulse

13
Q

Where is the SA node located?

A

In the Right Atrium where the SVC enters

14
Q

What are the 3 internodal tracts in the RA?

A

Anterior
Middle
Posterior

15
Q

How does the impulse travel from the RA to the LA

A

Bachmann’s bundle - near simultaneous contraction

16
Q

Where is the AV node located?

A

Inferior RA near the Cs Os

17
Q

How long does the AV node delay the impulse?

A

0.04ms

18
Q

Why does the AV node delay the impulse?

A

To allow ventricular filling from atrial contraction

19
Q

Describe the bundle of HIS

A

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

20
Q

What is the firing rate of the bundle of HIS?

A

40-60bpm

21
Q

Which bundle branch is thicker and why?

A

The left due to thicker LV wall

22
Q

Which bundle branch is faster and why?

A

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.

23
Q

Describe Purkinje fibres

A

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

24
Q

What is the pacemaker speed of Purkinje Fibres?

A

15-40bpm