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Since the world is three-dimensional, the vestibular system contains three semicircular canals in each labyrinth. They are approximately orthogonal (at right angles) to each other, and are the horizontal (or lateral), the anterior semicircular canal (or superior), and the posterior (or inferior) semicircular canal.
The semicircular canals are three semicircular interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the lateral, anterior and posterior semicircular canals. They are the part of the bony labyrinth, a periosteum-lined cavity on the petrous part of the temporal bone filled with perilymph.
Each semicircular canal (SSC) is a thin tube that doubles in thickness briefly at a point called osseous ampullae. At their center-base, each contains an ampullary cupula . The cupula is a gelatin bulb connected to the stereocilia of hair cells, affected by the relative movement of the endolymph it is bathed in. [ citation needed ]
The receptor cells located in the semicircular ducts are innervated by the eighth cranial nerve, the vestibulocochlear nerve (specifically the vestibular portion). The crista ampullaris itself is a cone-shaped structure, covered in receptor cells called "hair cells".
Head position is sensed by the utricle and saccule, whereas head movement is sensed by the semicircular canals. The neural signals generated in the vestibular ganglion are transmitted through the vestibulocochlear nerve to the brain stem and cerebellum. [18] The semicircular canals are three ring-like extensions of the vestibule.
Hearing: Cochlear duct: fluid waves in the endolymph of the cochlear duct stimulate the receptor cells, which in turn translate their movement into nerve impulses that the brain perceives as sound. Balance: Semicircular canals : angular acceleration of the endolymph in the semicircular canals stimulate the vestibular receptors of the endolymph.
Information from the semicircular canals reflects rotational movement of the head. Both are necessary for the sensation of body position and gaze stability in relation to a moving environment. Axons of the vestibular nerve synapse in the vestibular nucleus are found on the lateral floor and wall of the fourth ventricle in the pons and medulla.
The brain can then decide which muscles in the body need to become active in order to right itself. The semicircular canals have a superior, posterior, and horizontal component. Studies have shown that the horizontal canal is most correlated with agility, as shown with several mammals. [3]