Currents

Question 1

Explain how the pacemaker potential works?

Answer 1

At full hyperpolarisation the funny channel is activated - Decreases K+ Permeability and increases Na+

The Membrane potential slowly rises (aided by opening of some T-type Ca2+ channels) till it hits threshold (~-40mV)

At threshold L-type Ca2+ channels open and the cells rapidly depolarises firing an AP.

At full depolarisation Ca2+ channels close and K+ channels open, an efflux of K+ causes repolarisation.

Question 2

Explain how the non-pacemaker potential works?

Answer 2

Steady resting membrane potential is maintained by a high resting permeability to K+

Voltage gated Na+ channels open and Na+ floods the cell causes massive depolarisation.

Triggers opening of Ca2+ channels and closing of K+ channels which maintians plateu phase of depolarisation.

Ca2+ channels close and K+ open leading to repolarisation.

Question 3

How does Temp affect HR?

Answer 3

a rise of 1C = a rise of 10BPM

Question 4

How does Ivabradine work?

Answer 4

It inhibits the funny channel, slowing the pacemaker potential and so reducing HR

Question 5

How do CCBs work?

Answer 5

They reduce the amount of Ca2+ allowed into the cell thus reducing force of contraction

Question 6

How does hyperkalemia affect the heart?

Answer 6

Hyperkalemia

• > Loss of conc. gradient
• > K+ doesnt flow out of cell
• > Cell depolarises on its own
• > Random Contraction
• > Afib and AV block

(Hypokalemia does the same)

Question 7

How does hypercalcaemia affect the heart?

Answer 7

It increases Contraction strength by increasing calcium available to cell.
Also causes Ca2+ to flood the cell faster leading to a raised HR