Action Potential

1. MYOCYTIC POTENTIAL

• Phase 0: Upstroke or Rapid Depolarization

• Phase 1: Early Rapid Depolarization

• Phase 2: Plateau

• Phase 3: Final Rapid Repolarization

• Phase 4: RMP & Diastolic Depolarization

Phase 0: Upstroke or Rapid Depolarization

• Rapid inward rush of Na+ thru the fast channels

• Slow influx of Na+ and Ca+ thru slow channels

till it reaches -90 mv

inside of cell, more positive

Phase 1: Early Rapid Depolarization

Sudden closure of fast Na+ channels

Potassium deflux (as K+ is inside)

• Phase 2: Plateau

Balance between influx of Ca+ and outflow of K+

Potassium deflux but Ca+ influx so there is balance

• Phase 3: Final Rapid Repolarization

• Closure of Ca+ channels, continued K+ outflow (K+ Deflux)

• Phase 4: RMP & Diastolic Depolarization

Na+ and Ca+ channels close

K+ slowly leaks to the outside of the cell causing the inside of the cells to be (-) relative to the outside, which is (+)

(PISO) Potassium IN Sodium OUT

1. PACEMAKER POTENTIAL

• Phase 4: Unstable RMP

• Phase 0: Depolarization

• Phase 3: Repolarization

• Phase 4: Unstable RMP

(Na+ in) to Funny Na+ channel (Slow depolarization due to Na and Ca leak through Funny Na+ and Ca+ channel, if it hit membrane potential of -40 it will have depolarization

Slow depolarization because of leak (influx) of Ca+

(not RMP) - because (slow Na+ in (Funny Na+ channels are open)) (K+ channels close) due to Na+ and K+ Leak till it reaches - 40mV

Transient Calcium funny channels, push membrane potential to threshold, giving to action potential

• Phase 0: Depolarization

meet -40 (threshold)

Ca+ channel /L-type channel open (influx of Ca+)

Opening of Ca+ channel is responsible for rapid depolarization of SA node action potential

• Phase 3. Repolarization

Open potassium, close L-type Ca+ channel

Phase 4 - Na+ in through funny Na channel plus L type Ca+ channel till it reaches -40mV (Upstroke potential)

Slow depolarization

Phase 0- Ca+ channel open

Phase 3- Ca+ channel close, K+ Open