Which phase of cardiac action potential is caused by closure of the fast sodium channels? phase 0 phase 1 phase 2 phase 3?

phase 1

A cardiac action potential can be divided into phase 0-4. In phase 0, the sodium channel is opened and sodium will come into the cell which causes a rapid depolarization. In phase 1, the fast sodium channel is closed and K+ channel starts to be opened which makes a small repolarization.

The infrared (ir) and the ultraviolet(uv) represent the two extremities of the visible spectrum (400-700nm). while ir represents electromagnetic radiation with wavelengths longer than those of visible light, uv represents wavelengths shorter than visible light