Once an SA Nodal Cell Reaches Threshold, the Depolarization Phase

Multiple Choice

Once an SA nodal cell reaches threshold, the depolarization phase occurs during which

A) potassium comes in through fast voltage-gated channels.
B) calcium comes in through fast voltage-gated channels.
C) potassium moves out through fast voltage-gated channels.
D) sodium moves out through slow voltage-gated channels.
E) calcium moves out through slow voltage-gated channels.