Timothy C. Hain, MD • Last modified: February 17, 2021
We live in a three dimensional world and thus we can rotate along the three axes that define our world.
The inner ear must be able to register rotation about these three axes. The three semicircular canals -- the anterior, posterior and lateral canals, are arranged nearly perpendicularly in order to measure rotation in 3D space.
Although the canals are arranged nearly perpendicularly, there is not a canal for roll, for pitch and for yaw, but rather the canals register a mixture of these axes, which are resolved in the brain into meaningful coordinates.
The eyes move predominently in the direction of the canal being stimulated -- this is called Flourens' law. The eye movements from excitation are greater than inhibition -- this is called "Ewalds" 2nd and 3rd law -- the 2nd is for the horizontal canals, and the 3rd for the vertical canals.