semicircular canals


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Related to semicircular canals: utricle

Semicircular Canals

 

canals of the inner ear of vertebrate animals and man that help regulate equilibrium and body orientation. Fish, terrestrial vertebrates, and man have three semicircular canals arranged in three mutually perpendicular planes. There is a horizontal (in man, lateral) semicircular canal and two vertical ones—the anterior and the posterior. In fossil Agnatha and extant cyclostomes and petromyzons there are only two vertical semicircular canals, anterior and posterior. In Myxini there is one posterior canal.

The membranous labyrinth of the ear is filled with fluid endolymph and is located within osseous sheaths; the space between the membranous and the osseous labyrinth is filled with perilymph. Each semicircular canal ends in two branches, one of which is dilated to form an ampulla. The two adjacent branches of the vertical semicircular canals are united into a single common branch in most vertebrates; the semicircular canals open into the vestibule by five openings.

Each ampulla of the semicircular canals has sensory hair cells, grouped in a crista, or crest. Over the crista is a gelatinous cupula, into which these hair cells enter. The bases of the sensory cells are entwined with fibers of the vestibular nerve, which transmit excitation to the brain. Changes in the position of the head or body, accompanied by shifting of the cupulae and endolymph, and by displacement of the otoliths suspended in the endolymph, cause stimulation of the hairs and of the sensory cells of the semicircular canals. This leads to the transmission of an electrical discharge along the nerve and into the brain. From the brain the nerve impulses are directed to the muscles and the other organs that regulate the body’s orientation.

G. N. SIMKIN

semicircular canals

semicircular canalsclick for a larger image
The two sets of three canals in the human ear, which are at right angles to each other. The set of semicircular canals acts to sense angular rotation about each of the three axes. Each of the canals is filled with fluid, and there is a flaplike structure called a cupula at the end of each canal.
These canals are the main vestibular organs that give us a sense of spatial orientation in the absence of visual clues. The system is unable to sense small angular velocities and thus is nearly useless in flight, often sending false signals to the brain.
References in periodicals archive ?
Inner ear presentations of patients include dysplastic vestibule, cochlear hypoplasia with defective modiolus, EVA, hypoplastic semicircular canals, and dilated internal auditory canals.
In the literature, it has been determined that the worst prognoses are for cochlear fistulas and the best are for fistulas of the lateral semicircular canal (10).
Superior semicircular canal dehiscence presenting as conductive hearing loss without vertigo.
BPPV is often accompained with nausea, vomiting, (27) and is usually caused by dislodged otoconia in the posterior semicircular canal. Episodic vertigo continues for many weeks and then resolves spontaneously, but, in some cases, it is recurrent.
Maximum malformations found in a single ear were 7 structural malformations which included malformation of cochlea, modiolus, vestibule, vestibular aqueduct, semicircular canals, internal auditory canal, and vestibulocochlear nerve.
This study aimed to develop an FE model for a human membranous labyrinth, including the utricle and three membranous semicircular canals, and to examine the vestibular response to a caloric test with different head positions.
"Almost in every case where there is a fossilized skull, the semicircular canals are present and well preserved," Timothy Ryan, assistant professor of anthropology, geosciences and information sciences and technology, Penn State, said.
Vertigo may originate in the vestibular system, consisting of the fluid-filled semicircular canals and the utricle, hair cells topped with crystals known as otoconia.
* The vestibular system of each inner ear (semicircular canals, utricle and saccule) controls rotatory movements and orientation in, to and fro, up and down, and angular movements.
BPV occurs when otoconia dislodge from the utricle and lodge in the semicircular canals. During head movement, the otoconia can stimulate the canals, which is interpreted as a sense of whirling dizziness and unbalance.