Since we cannot easily create a long duration microgravity environment in the classroom, this demonstration instead models this effect with the expansion being caused by a change in air pressure. A column of discs is separated by marshmallows, and the whole placed into a vacuum chamber. As the pressure is reduced, the gas in the marshmallows expands, forcing apart the spinal discs. When pressure returns, the spine collapses back, much like astronauts experience when they return to Earth.
Challenge your students to think of other body parts and processes that could be similarly affected by changes in gravity.