Electro/Muscle physiology - Zachow

Question 1

Hyperkalemia

Answer 1

Initialy: increased excitability

Progresses to have Vm clamped at less neg V, so as voltage gated NA+ channels close over time, the Na+ resting levels become inactive Na+ channels, which decreases the excitability overall

Question 2

Pacemaker Potential

Answer 2

1. SLOW DEPOL: begins every time we reach a (-) membrane potential, due to 3 currents, which allow a little more + out than in
   T-type Ca2+ channels allow slow inward Ca2+ current
   HCN channels allow slow inward Na+ current
   Outward flow of K+
2. RAPID DEPOL: threshold reached from slow depol
   Inward Ca2+ current due to opening voltage gated Ca2+ channels
3. REPOL/HYPERPOL: voltage gaged K+ channels open

Question 3

Plateau Potentials

Answer 3

• Phase 0: RAPID DEPOL dependent on opening of Na+ channels (which is dependent on current from atria)
• Phase 1: TRANSIENT REPOL stimulated by special K+ channels, which are responding to + membrane pot
• Phase 2: PLATEAU PHASE due to change in membrane pot Ca2+, Na+ & another type of K+ open
• Phase 3: REPOL COMPLETED by opeing of another K+ channel
• Phase 4: Resting