が in the expression "耳が聞こえない"


I tried to translate this phrase literally and came up with "(My) ears can't
hear". Since the expression means "(I'm) deaf", this makes sense.  
However, I can't really get it to work grammatically, seeing as が isn't
normally used to denote the subject in sentences with a "potential"-form.  
So how can が be grammatically explained in this expression?  
Thanks for reading through my question.

