switch to previous buffer

[Rami A]

Usually I switch between buffers going through the "buffer menu".
So I would be in Buffer 1 -> C-x C-b "bufer menu" -> buffer 2

I have the short cut:
(global-set-key "\M-a" 'switch-to-previous-buffer)

So I could switch back to the previous buffer.
How is possible to skip the buffer menu when doing so.

Basically,
Buffer 1 -> C-x C-b "bufer menu" -> buffer 2 -> M-a -> buffer 1 "without going 
back to buffer menu"