How do I call AxesStyle->Arrowheads[ ] in order to control whether or not an arrow appears on each of the four ends of the axes in a Plot, and if it does appear how to control the size of each one?

Here's an example:

Plot[1/x^5, {x, -20, 20}, AxesStyle -> Arrowheads[{-.02, 0}],


It seems Axes->Arrowheads[.05] makes all 4 of them appear and appear at the same size, while Axes->Arrowheads[{-.05,.05}] makes them appear in "pairs". But sometimes I just want the "north" and "west" axes to have arrows and nothing else.

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AxesStyle takes a list {x style, y style} so for "north" and "west" arrows only:
Plot[1/x^5, {x, -20, 20},

Ah, thanks. I had tried Arrowheads[{{a,b},{c,d}}] when I should have been using Arrowheads[{a,b}],Arrowheads[{b,c}] – JohnD Oct 21 '13 at 22:50