There are definitely more shades of vert than intro and extro. This chart is fun in showing that there is a continuum in the personality type scheme.

Some people are in the middle of the intro-extro spectrum. Energized by people at times, exhausted by people at other times. Myers-Briggs is useful in reminding us that people have different ways of responding to the universe. Myers-Briggs is irritating when people think that they actually have a "type" that is static and measurable.