Notts took the lead against the run of play after 18 minutes when Curtis Thompson pulled the ball across the area and Jeff Hughes scored.
The visitors equalised in the 37th minute when, after a terrific passing move, Andrew Bond's low cross gave Jabo Ibehre a simple tap-in on the line.
The half-time whistle was delayed when U's defender David Wright came off worst in a clash of heads with Joss Labadie right on the 45 minute mark, and after a lengthy stoppage of more than 10 minutes the full-back had to be carried from the field on a stretcher.
County restored their lead after 77 minutes when sub Arquin met a Alan Sheehan corner with a terrific looping header over goalkeeper Sam Walker.
Youngster Nangle then came off the bench to seal the win for the Magpies in stoppage time when he coolly slotted home an Enoch Showunmi cross.