The semicircular canals are part of the inner ear.
They are lined with cilia (microscopic hairs) and filled with a liquid substance, known as endolymph. Every time the head moves, the endolymph moves the cilia. This works as a type of motion sensor, as the movements of the cilia are communicated to the brain. As a result, the brain knows how to keep the body balanced, regardless of the posture.
The semicircular canals of each ear contain three main parts: anterior, posterior, and horizontal canals. Each of these canals provides a separate sense of directional balance, and each canal on the left is always paired with a canal on the right for normal function. The anterior canal detects forward and back head movement, like nodding. The posterior canal detects head tilt like tipping the head toward the shoulders. The horizontal canal detects horizontal movement of the head, such as swiveling the head side to side.
Damage or injury to the semicircular canals may be twofold. If any of the three separate pairs do not work, a person can lose their sense of balance. A loss of hearing may also result from any damage to these semicircular canals.