The semicircular canals consist of three ducts arranged on three perpendicular planes. At the end of each canal is a swelling called an ampulla.
The semicircular canals are filled with fluid called endolymph. When we move our bodies, the fluid inside the semicircular canals moves as well. Its movement is detected by hair-like projections called cilia, and then this information is sent to the auditory nerve, where it is processed by the brain.
The Inner Ear. Accessed: October 26, 2009 from http://hyperphysics.phy-astr.gsu.edu/hbasees/Sound/eari.html