Movement of fluid in the semicircular canals signals the brain about the direction and speed of head rotation. In other words, it lets the brain know if you are nodding your head up and down or looking right to left. Each semicircular canal has a bulbous end that contains hair cells. Rotation of the head causes a flow of fluid, which in turn causes displacement of the top portion of the hair cells that are embedded in the jelly-like cupula.



The figure above shows nerve activity associated with rotational-induced physiologic nystagmus and spontaneous nystagmus resulting from a lesion of one labyrinth. Thin straight arrows—direction of slow components; thick straight arrows—direction of fast components; curved arrows—direction of endolymph flow in the horizontal semicircular canals: AC—anterior canal, PC—posterior canal, HC—horizontal canal.

The more you know, the less you’ll suffer.
