Since the universe is expanding, does that mean our heads are getting bigger, too?

Not yet as the other forces such as weak, strong, electromagnetic and gravity overcome the slight amount of expansion. It's sort've like pulling a tablecloth out from under the dishes, everything just slides over the tablecloth. However, one hypothesis for the end of the universe is when the expansion becomes so fast that the other forces can't keep sliding everything back together over the expanding space, since the four forces all drop off with distance, everything would fly apart in the Big Rip.

Mind you, maybe your head is getting bigger.

Macro and micro have nothing to do with it.

Only in deep intergalactic space where gravity fields and all other fields are extremely weak can the expansion happen. In that deep intergalactic space, galaxies and distant atoms alike move away from each other because of the expansion. Your head is held together with chemical bonds of various levels and material strengths and those are much stronger than the expansion of space, so the expansion simply does not happen in your head.

It's working at every level. However, on the small scale such as inside galaxies (so definitely inside our bodies....) gravity and the other forces are powerful enough to overcome the expansion. So in effect, yes it's only happening on the "macro", intergalactic, scale.

The universe isn't actually expanding at all. The idea that it does comes from misinterpreting galactic redshifts as a doppler effect when they are actually a scattering effect. The galaxies are not generally receding from each other at all. Their light simply loses energy through it's interaction with the intergalactic medium... http://www.newtonphysics.on.ca/universe/

If the universe was expanding quasars would show time dilation effects but they don't:

http://phys.org/news190027752.html

This documentary may enlighten you:

http://www.youtube.com/watch?v=1yTfRy0LTD0&playnex...

Right now its mostly affecting the Space between Galaxies and Galactic Clusters, but yes, one day in inconceivable reaches of Time, yes, all Matter will fly apart.

The Big Rip happens.

No, it doesn't mean that.

The universe is expanding at a cosmological level. Galaxies are receding - the farther the galaxy the faster it is receding.

But local gravity (such as within the Local Group, our galaxy, our solar system, or our heads) is stronger than expansion.

I don't know about bigger, but some heads are definitely getting emptier.

No, it means everything is getting farther apart. Things themselves aren't stretching.