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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 ...
Dynamic balance is provided through the three semicircular canals. These three canals are orthogonal (at right angles) to each other. At the end of each canal is a slight enlargement, known as the ampulla, which contains numerous cells with filaments in a central area called the cupula. The fluid in these canals rotates according to the ...
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.
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]
These inertial properties are dependent on the vestibular system, especially the semicircular canals of the inner ear, which signal rotations of the head. [23] The HD system integrates the vestibular output to maintain a signal reflecting cumulative rotation. The integration is less than perfect, though, especially for slow head rotations.
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.
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.