cmos - NMOS: what exactly forms the inversion layer

I have a a question on forming of the inversion layer in NMOS. More specifically, please refer to the following figures

The negative ions (in-mobile) are due to the the accumulation of the positive charges at the gate metal plate that pushes the holes (mobile carriers) downward. This is the first figure. However, in the second figure, there is electrons moving on top of the negative ions. And I question is, is the mobile electrons forming the inversion layers (connect the source to the drain), or does the in-mobile negative ions forming the inversion layer?

This confuses me if you look at another diagram (below). If you look at the place underneath the oxide, marked as "Induced n-type channel", it is hard for me to tell which is which