Semicircular canal

The semicircular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three orthogonal planes. The vertical canals are positioned at an angle of about 100 degrees relative to one another, while the horizontal canal makes an angle of about 95 degrees with the posterior canal and an angle of about 110 degrees with the anterior canal. Deviations up to 10-15 degrees between individuals are normal. Because the angles between the canals are not perpendicular, movements of the head stimulate horizontal and vertical canals simultaneously.

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The three canals are:

• Horizontal semicircular canal; detects rotation of the head around a vertical axis (i.e. the neck), as when doing a pirouette.
• Superior semicircular canal; detects rotations of the head in the sagittal plane, as when nodding.
• Posterior semicircular canal; detects rotation of the head around a rostral-caudal (anterior-posterior) axis, as when cartwheeling.

Each canal is filled with a fluid called endolymph and contains a motion sensor with little hairs (cilia) whose ends are embedded in a gelatinous structure called the cupula.

The Semicircular canals are a component of the Labyrinth.

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