Cardiac Action Potentials (E1)

Question 1

What is the resting membrane potential of a cardiac muscle cell?

Answer 1

-80 mV

Question 2

Discuss the Action potential of a cardiac muscle cell?

Answer 2

1. L-type Calcium channels open in CM
2. Small amount of Ca enters cell.
3. Triggers more Ca release from SR
4. Ca concentration increases by 1000
5. Activation of troponin
6. Cross-bridge cycling (Contraction)

Question 3

Discuss the Repolarization of a cardiac muscle cell.

Answer 3

1. Ca pumped back into SR or out of cell
2. Ca concentration drops
3. Deactivation of troponin (Relaxation)

Question 4

Describe how an AP spreads across the heart.

Answer 4

1. Pacemaker cells in SA node spontaneosly depolarize
2. AP spreads across atria (Atria contract)
3. AP slowly goes through AV node ( AV delay)
4. AP spreads quickly through both ventricles (Ventricles contract)

Question 5

How does the length of an AP in cardiac muscle compare to skeletal muscle APs?

Answer 5

Both Atrial and Ventricular APs are longer than skeletal APs.

Question 6

What causes the refractory period in cardiac muscle?

Answer 6

Inactivation of Na channels; RP is 250ms

Question 7

Why is the refractory period and AP in cardiac muscle so important?

Answer 7

Guarantees time for relaxation and prevents tetanus.

Question 8

Discuss ion permeability in APs of cardiac muscle.

Answer 8

Rest: K permeability is high, Na and Ca permeability is low.
Depolarization: Na permeability is high
Partial Repolarization: Na permeability is low
Plateau: K permeability is low, Ca permeability is high
Repolarization: K permeability is high, Ca permeability is low.