Imagine your mind consists of everything blue that is our planet. (No testicle puns please)
The air is above the sea; and as such it dominates and extends itself. The air is your first four functions. Below that, the depths of the sea swirl in currents, violently, placidly. The sea is your shadow functions.
But just because your first functions are more prevalent doesn't mean that your shadow functions are expunged at any given time. They are both there in circumspect at all times.
Just because some synapses fire most frequently doesn't mean that the others cease all together.