Node asynchronous route code

I'm using node with express 4.0. I can't find anything on the internet (including the docs) about embedding asynchronous code in a route.

With a middleware it's quite simple:

app.use('/something', function (req, res, next)
{
  doSomethingAsync(function(err, probablySomethingElse)
  {
    // probably some error checking
    next();
  });
});

The problem with routes is that there is no next callback, so how does express know when to move to the next job?

app.get('/something', function (req, res)
{
  res.render('someTemplate');
  // no next() here, but it still works
});

If I had to guess, I'd say that express moves to the next task right after the above function exits. But out of curiosity I've launched the following code...

app.get('/something', function (req, res, next)
{
  console.log(next);
});

...and there actually is some next callback passed. So what's going on here? How does it work behind the scenes? And how can I put asynchronous code there?