Cardiac APs

Question 1

name the channels involved in each phase

Answer 1

• phase 0: inward Na current
• phase 1: outward K current through “outward rectifier channel”
• phase 2: plateu phase caused by inward Ca channel
• phase 3: rapid repolarization by outward K channel through delayed rectifier K channel
• phase 4: resting, stable potential at -85 mV

Question 2

name channels involved in each phase of the SA node AP

Answer 2

• phase 4: i_f and i_Ca open to partially depolarize cell
  
  • if = Na channels
  • iCa = T-type (transient)
• phase 0: inward Ca current causing the upstroke depolarization
  
  • Ca channels = L-type Ca channels (long)
• phase 3: outward K current
  
  • Ca channels close and K channels open

Question 3

describe the path of depolarization in heart

Answer 3

• AP initiated in the SA node trave to AV node where conduction is slowed (holds it for .09 sec)
  
  • this delay allows time for the atria to complete contraction
• wave depolarizes bundle of His (L + R branches)
• wave then travels to Purkinje fibers; depolarized fastest

Question 4

describe the effect of ACh on heart rate

Answer 4

Question 5

describe the effect of NE and Epi on HR

Answer 5