According to Scardino in "The Prostate Book", "The  neurovascular
bundele (NVB) containing the cavernous (erectile) nerves runs alongisde
the rectum and passes along the prostate and the urinary sphincter into
the penis".  If I  understand correctly, the nerves are not actually
visible, but a skilled experienced surgeon can tell where they are.
Unless it is necesasry to excise the cancer, the nerves are not cut.
The prostate is separated from the nerve bundle and removed, leaving the
nerves intact.  However, even with a very skilled surgeon, there is
going to be some trauma to the area.  So it usually takes several months
for erections to return and it can take two years or even longer.

Before nerve sparing surgery was developed, urologists didn't realize
that the erectile nerves were outside the prostate and that it could be
removed without affecting them.   It was thought that impotence was
inevitable after radical prostatectomy, but uorologists were surprised
to find that some of their patients regained erections.   The correct
anatomy was discovered by Patrick Walsh, of Johns Hopkins, and Pieter
Donker, a Dutch medical scientist.  Walsh is credited with inventing
nerve sparing technique.

This is a question for Dr, Yew! Maybe he'll explain  it.

I don't think they are as large as cooked spaghetti - I've always heard they
are more like trying to peel wet toilet paper off a skinless plum. So I will
assume when they transplant a nerve they have to go back to the "base" area
of the nerve and attach it there. But what they do with those peel nerves -
I have no idea.
Bev