Vestibular system

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Related to Vestibular disease: Vestibular neuritis, Vestibular disorders

Vestibular system

The system that subserves the bodily functions of balance and equilibrium. It accomplishes this by assessing head and body movement and position in space, generating a neural code representing this information, and distributing this code to appropriate sites located throughout the central nervous system. Vestibular function is largely reflex and unconscious in nature.

The vestibular labyrinth is located within the inner earenlarge picture
The vestibular labyrinth is located within the inner ear

The centrifugal flow of information begins at sensory hair cells located within the peripheral vestibular labyrinth. These hair cells synapse chemically with primary vestibular afferent nerve fibers, causing them to fire with a frequency code of action potentials that include the parameters of head motion and position. These vestibular afferents, in turn, enter the brain and terminate within the vestibular nuclei and cerebellum. Information carried by the firing patterns of these afferents is combined within these central structures with incoming sensory information from the visual, somatosensory, cognitive, and visceral systems to compute a central representation of head and body position in space. This representation is called the gravito-inortial vector and is an important quantity that the central nervous system employs to achieve balance and equilibrium. See Brain, Nervous system (vertebrate), Postural equilibrium, Reflex

The vestibular labyrinth is housed within the petrous portion of the temporal bone of the skull along with the cochlea, the organ of hearing (Fig. 1). The receptor element or primary motion sensor within the labyrinth is the hair cell (Fig. 2). Hair cells respond to bending of their apical sensory hairs by changing the electrical potential across their cell membranes. These changes are called receptor potentials, and the apical surface of the hair cell thus functions as a mechanical-to-electrical transducer. The frequency of the resulting action potentials in the VIIIth cranial (vestibulocochlear) nerve encodes the parameters of angular and linear motion. See Biopotentials and ionic currents, Ear (vertebrate), Synaptic transmission

Otolithic macula at restenlarge picture
Otolithic macula at rest

Hair cells are the common sensory element in both the angular and linear labyrinthine sensors as well as within the cochlea. The particular frequency of energy that hair cells sense within these diverse end organs arises because of the accessory structures surrounding the hair cells. Thus, angular motion is sensed by the semicircular canals, linear motion by the otolith organs, and sound energy by the cochlea.

The primary afferents innervated by hair cells are the peripheral processes of bipolar neurons having cell bodies located in Scarpa's ganglion within the internal auditory meatus. The central processes of these cells contact neurons in the brainstem of the central nervous system. The vestibular nuclei complex is defined as the brainstem region where primary afferents from the labyrinth terminate. It is composed of four main nuclei: the superior, medial, lateral, and descending nuclei. The axonal projections of vestibular nuclear neurons travel to all parts of the neuraxis, including the brainstem, cerebellum, spinal cord, and cerebrum. See Motor systems

In all vertebrates, there is an efferent system that originates from cell bodies within the central nervous system and terminates upon labyrinthine hair cells and primary afferents. The efferent vestibular system is presently a subject of intense study but undoubtedly is in place to enhance vestibular function. It is interesting that evolution felt it necessary to modify incoming vestibular information before it could enter the central nervous system.

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Two years after initial presentation, the bird's vestibular disease had not progressed.
In most cases of idiopathic vestibular disease, the dog's symptoms have a sudden onset and resolve over a few days or weeks.
Research findings reveal that old dogs suffering from idiopathic vestibular disease recover after use of nonspecific and supportive treatment.
Unidirectional nystagmus, where the direction of nystagmus is unchanged by change in direction of gaze (slow phase towards the dysfunctional labyrinth), is typical of peripheral vestibular disease, and will be most evident when looking in the direction of the fast phase.
It is the most common vestibular disease effecting women more frequently than the men2.
This report correlates the clinical presentation, imaging, and histopathologic findings in a macaw with central vestibular disease and demonstrates how advanced imaging techniques can identify hemorrhagic lesions through the T2* sequence.
have established that patients with peripheral vestibular disease often report symptoms of Dp/Dr [10].
Rotary chair, on the other hand, is gaining a unique presence in the vestibular testing market, on the back of unparalleled analysis offered by rotational testing for evaluation of both central and peripheral vestibular diseases. Future prospects of rotary chair will remain bullish, with palpability of more affordable advancements in the area, such as booth-less rotary chair.
The results indicated most vertigo or dizziness are attributable to the above diseases, as Furman et al described that the most common causes of vertigo are benign paroxysmal positional vertigo, Meniere's disease, migraine.20 Among 341 patients with certain diagnoses in our study, 111 patients (diagnosed as peripheral vestibular diseases) occupied 32.55%.
Vertigo, Nausea, Tinnitus, and Hearing Loss in Central and Peripheral Vestibular Diseases. Proceedings of the XXIInd Annual Meeting of the International Neuro-otologic and Equilibriometric Society; Hakone, Japan; April 6-9, 1995.
In addition to the otologic exam for vestibular diseases, patients should be screened for migraine, traumatic brain injury, dysautonomia, and dysrhythmias.
Genetic contribution to vestibular diseases. J Neurol 2018 Mar 26.