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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 lateral semicircular canal (also known as horizontal or external semicircular canal) is the shortest of the three canals. Movement of fluid within its duct corresponds to rotation of the head around a vertical axis (i.e. the neck), or in other words, rotation in the transverse plane. This occurs, for example, when one turns the head from ...
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 semicircular canals are filled with endolymph due to its connection with the cochlear duct via the saccule, which also contains endolymph. It also contains an inner membranous sleeve that lines the semicircular canals. The canals also contain the crista ampullaris.
The primitive lampreys and hagfish, however, have a simpler system. The inner ear in these species consists of a single vestibular chamber, although in lampreys, this is associated with a series of sacs lined by cilia. Lampreys have only two semicircular canals, with the horizontal canal being absent, while hagfish have only a single, vertical ...
Humans have semicircular canals, neck muscle "stretch" receptors, and the utricle (gravity organ). Though the semicircular canals cause most of the reflexes which are responsive to acceleration, the maintaining of balance is mediated by the stretch of neck muscles and the pull of gravity on the utricle (otolith organ) of the inner ear. [2]
The vestibular nerve travels from the vestibular system of the inner ear. The vestibular ganglion houses the cell bodies of the bipolar neurons and extends processes to five sensory organs. Three of these are the cristae located in the ampullae of the semicircular canals. Hair cells of the cristae activate afferent receptors in response to ...
The balance system works with the visual and skeletal systems (the muscles and joints and their sensors) to maintain orientation or balance. Visual signals sent to the brain about the body's position in relation to its surroundings are processed by the brain and compared to information from the vestibular and skeletal systems.