Action Potentials in Autorhythmic Cells

Pacemaker potential

a pacemaker cell membrane’s slow drift to threshold after an AP just occurred

What is the threshold in Action Potentials in Autorhythmic Cells?

-40 mv

What does Action Potentials in Autorhythmic Cells never do?

They are never at rest

Action Potential

all-or-non synchronized depolarization and repolarization of the cell caused the movement of ions

What are the four channels of Action Potentials in Autorhythmic Cells?

If channel, Transient Ca2+ channels (T-type), Long-lasting Ca2+ (L-type), and K+ channel

Which channels are the Pacemaker Potential?

If channels & Transient Ca2+ channels (T-type)

Which channels are the Action Potential?

Long-lasting Ca2+ (L-type) & K+ channel

If channels

open upon membrane hyperpolarization (voltage at -60 mv)

The If channel will have…

Na+ influx

What is the result of If channel

Inward Na+ current potential depolarizes closer to threshold

Transient Ca2+ channels (T-type)

Voltage-gated & open for a short amount of time

The Transient Ca2+ channels (T-type) will have…

Ca2+ influx

What is the result of Transient Ca2+ channels (T-type)

Brief, Inward Ca2+ current

Long-lasting Ca2+ (L-type)

Voltage-gated & open for a longer period of time

The Long-lasting Ca2+ (L-type) will have

Ca2+ influx

What is the result of Long-lasting Ca2+ (L-type)

Large influx of Ca2+

K+ channel

Voltage-gated, open at the peak of the AP

The K+ channel will have

K+ efflux

What is the result of K+ channel

K+ efflux

Which channels of Action Potentials in Autorhythmic Cells are responsible for the falling phase of AP

K+ channel

What causes the If channels to open? Phase 1

Negative membrane potential (-60mV)

Which channel opens? And What does it allowed? Phase 1

If channels opens allowing an influx of Na+

What is the effect of Na⁺ influx through If channels? Phase 1

Depolarization

What happens to voltage-gated K⁺ channels at Phase 1?

They are closing

What is the result of K⁺ channel closure? Phase 1

Decreased outward K+ current

During Phase 2 of action potentials in autorhythmic cells, what happens as the membrane depolarizes toward threshold?

If channels close

Why do the If channels close during phase 2?

They only open at -50mV

What does the depolarizing membrane towards the threshold stimulate to open? Phase 2

Transient Ca2+ channels (T-type)

Phase 2 will have…

Na+ influx & Ca2+ influx

At what membrane potential does Phase 3 begin in autorhythmic cells?

-40mV

What happens to Transient Ca2+ channels (T-type) when threshold is reached? Phase 3

They close

Which channels open at threshold potential during Phase 3?

Long-lasting Ca2+ (L-type)

What is the effect of opening Long-lasting Ca2+ (L-type) channels? Phase 3

Rapid depolarization

What does the electrical propagation of the action potential lead to? Phase 3

depolarization of SA node

Phase 3 will have….

Ca2+ influx

What happens to Long-lasting Ca2+ (L-type) as the membrane potential peaks in Phase 4?

They begin to close

Which channels begin to open during Phase 4?

voltage-gated K+ channels

How do voltage-gated K+ channels open in Phase 4?

slowly

Phase 4 will have….

K+ efflux

What is the main event during Phase 5 of autorhythmic cell action potentials?

Rapid repolarization

What causes the membrane to repolarize during Phase 5?

K+ leaves the cell through voltage-gated K+ channels

At approximately what membrane potential do If channels open again? Phase 6

-60 mV

What happens when the membrane potential becomes very negative in Phase 6?

If channels open