Which current is mainly responsible for the spontaneous phase 4 depolarization of the sinoatrial node?
Answer and explanation
Correct answer: C. The 'funny' current (If), a slow inward sodium current
- Step 1: SA node cells have no stable resting potential. Step 2. The hyperpolarization-activated funny current slowly depolarizes the cell to threshold. Answer: the funny current. Why not the others: the fast sodium channel is absent in nodal cells, and outward potassium current would hyperpolarize the cell.
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