Semicircular Canal | Anatomy - Britannica

Function

The semicircular canals work together to sense rotational and angular movements of the head. They sense motion via the ampulla, a bulb-shaped structure at the base of each canal. The ampulla contains a fluid known as endolymph, which is also present in the cochlea, and the crista, a cone-shaped structure lined with hair cells and supporting cells. The hair cells form stereocilia, protrusions that extend into the crista. The longest of the stereocilia are the kinocilia, which point in a single direction and are sensitive to movement. The kinocilia extend from the crista into the cupula, a jellylike mass that surrounds the hair cells completely, separating them from the endolymph.

More From Britannica vestibular system: Semicircular canals

The crista is flexible. When the head moves, endolymph pushes the cupula one way or the other, which in turn displaces the hairs and alters the electrical potential of the hair cells. A change in potential is linked to the flow of potassium ions through mechanically gated ion channels in stereocilia. When movement causes stereocilia to bend toward the kinocilium, ion channels open, allowing for the flow of potassium ions into the cell and resulting in depolarization; when movement causes stereocilia to bend away from the kinocilium, ion channels close, preventing potassium ions from entering and resulting in hyperpolarization. The change in polarization causes the corresponding neurons to send impulses to the central nervous system. The information transmitted by the neural impulses enables agile mobility of the body and head and stability of vision while moving. The phenomenon of dizziness that is associated with certain head movements is caused by inertia of the endolymph, which continues to move for a short while after the head stops moving.

Each semicircular canal in one ear functions in tandem with a canal in the opposite ear. The left anterior canal pairs with the right posterior canal; likewise, the right anterior canal pairs with the left posterior canal. The lateral canals also form a pair. These relationships allow the vestibular apparatus to perceive the orientation of the head in three-dimensional space and enable the visual system to fixate on a point while the head is moving.

Key People: Yves Delage Josef Breuer (Show more) Related Topics: semicircular duct ampulla of semicircular canal posterior semicircular canal lateral semicircular canal crista ampullaris (Show more) See all related content