/sci/ - Science & Math

I'm trying to make sense of this circuit that tells a motor to switch directions when certain pressure buttons are pressed, but I'm having some problems understanding why certain elements are there. I've marked them for clarity.

The upper part of the network (pin 4+5) is supposed to be a system that works as follows:
It drives a motor that can switch direction of rotation by means of a relais. Pin 5 does this. If a 1 signal (3.3V) comes from pin 5, a voltage difference is created over the coil and the motor changes directions (the switch closes). If pin 5 outputs a 0 signal the 12V will let straight into the ground. Pin 4 is just there for putting the motor on and off; if it outputs a 1 signal (3.3V) the motor will rotate, if it outputs nothing it won't.

The lower part of the network (pin2+3) is meant to interpret the signals of the pressure buttons. When one of the buttons is pressed, this information should be send to the microcontroller (the pins) so that a written program can then make the motor stop rotating, switch rotational direction and start rotating again. Supposedly the microcontroller also has a quasi infinite resistance for some reason, which I'm very much confused by.

Is there anyone here who understands the functions of the marked elements or can in other ways help to interpret this circuit. Any help would be very much appreciated.