Semicircular canal

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Semicircular canal
Blausen 0329 EarAnatomy InternalEar.png
The internal ear, with "semicircular ducts" at left
Vestibular system's semicircular canal- a cross-section.jpg
Latin canalis semicircularis
stylomastoid artery
Gray's p.1049
MeSH A09.246.63
TA A15.3.03.015
FMA FMA:75362
Anatomical terminology

A semicircular canal or a semicircular duct is one of three semicircular, interconnected tubes located inside each ear. The three canals are:

  • the horizontal semicircular canal (also known as the lateral semicircular canal),
  • superior semicircular canal (also known as the anterior semicircular canal),
  • and the posterior semicircular canal.


The anterior and posterior semicircular ducts are oriented vertically at right angles to each other. The lateral semicircular duct is about 30-degree angle from the horizontal plane. The orientations of the ducts cause a different duct to be stimulated by rotation of the head in different planes. Thus, the horizontal canal detects horizontal head movements (such as when you spin in a rotating chair), while the superior and posterior canals detect vertical head movements (such as when you bend forward to pick something up from the floor).[1]

The semicircular canals are a component of the bony labyrinth. Among species of mammals, the size of the semicircular canals is correlated with their type of locomotion. Specifically, species that are agile and have fast, jerky locomotion have larger canals relative to their body size than those that move more cautiously.[2]

Horizontal semicircular canal[edit]



Superior semicircular canal[edit]

The superior semicircular canal (anterior semicircular canal) is a part of the vestibular system and detects rotation of the head around a rostral-caudal (anterior-posterior) axis, or in other words rotation in the coronal plane. This occurs, for example, when you move your head to touch your shoulders, or when doing a cartwheel.

It is 15 to 20 mm in length, is vertical in direction, and is placed transversely to the long axis of the petrous portion of the temporal bone, on the anterior surface of which its arch forms a round projection. As part of the vestibular system it detects rotation of the head around a rostral-caudal (anterior-posterior) axis. It describes about two-thirds of a circle. Its lateral extremity is ampullated, and opens into the upper part of the vestibule; the opposite end joins with the upper part of the posterior canal to form the crus commune, which opens into the upper and medial part of the vestibule.

Posterior semicircular canal[edit]


It is directed superiorly, as per its nomenclature, and posteriorly, nearly parallel to the posterior surface of the petrous bone. The vestibular canaliculus is immediately medial to it. It is part of the bony labyrinth and is used by the vestibular system to detect rotations of the head in the sagittal plane. It is the longest of the three canals, measuring from 18 to 22 mm. Its lower or ampullated end opens into the lower and back part of the vestibule, its upper into the crus commune.


Findings from a 2009 study demonstrated a critical late role for bmp2b in the morphogenesis of semicircular canals in the zebrafish inner ear. It is suspected that the role of bmp2 in semicircular canal duct outgrowth is likely to be conserved between different vertebrate species.[3]


Each canal is filled with a fluid called endolymph and contains motion sensors within the fluids. At the base of each canal, the bony region of the canal is enlarged which opens into the utricle and has a dilated sac at one end called the osseous ampullae. Within the ampulla is a mound of hair cells and supporting cells called crista ampullaris. These hair cells are composed of many cilia and embedded in a gelatinous structure called the cupula. As the head rotates the duct moves but the endolymph lags behind. This deflects the cupula and bends the cilia within. The bending of these cilia alters an electric signal that is transmitted to the brain. Within approximately 25–30 seconds of constant motion, the endolymph catches up to the movement of the duct and the cupula is no longer affected, stopping the sensation of acceleration.[1]



See also[edit]




  4. ^ Antunano, Melchor J. "FAA: Medical Facts for Pilots". Federal Aviation Administration. Retrieved 8 Dec 2011. 

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