Vestibular system


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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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The central vestibular system has four functional connections from the vestibular nuclei, namely:
Naegel, "Central vestibular system modulation in vestibular migraine," Cephalalgia, vol.
In conclusion, our results support the hypothesis that visual deprivation and proprioceptive perturbation could be compensated using other sensory strategies as vestibular system and that this approach may be useful to improve gait in PD patients.
As an experimental intervention, it was also suggested that the ill-at-ease feeling we had reproduced in vitro be regarded in vivo as a warning signal that she needed to readjust her posture to calm the internal conflict building up between the damaged vestibular system and her visual system.
If the patient's eyes stay locked on the distance target (no corrective saccade), the peripheral vestibular system is intact.
It all comes together in your inner ear, where the so-called labyrinth -- the centerpiece of your balance or vestibular system -- sends data to your brain.
To this end, and focusing on the squid vestibular system, we developed a fluorescent immunohistochemical procedure to stain the major cell types in the sensory epithelia of the squid statocyst, laying the groundwork for exploration of the squid system using diverse molecular and molecular imaging techniques.
Thepathology, symptomatology and diagnosis of certain common disorders of the vestibular system.
Today, in addition to removing his own shoes, Sandler coaches others in going barefoot, including the elderly, disabled veterans, and patients recovering from limb and brain injuries, posttraumatic stress disorder, and problems with the vestibular system.
One of the most common dizziness disorders, benign paroxysmal positional vertigo, or BPPV, occurs when calcium crystals in the utricle, one of the structures comprising the vestibular system, break loose and stimulate sensory hair cells, causing mild to intense spinning sensations.
It is an individualised exercise-based rehabilitation program which consists of specific head, body and eye exercises that are designed to retrain the brain to process and integrate the information from the vestibular system in order to create a central nervous system compensation for inner ear impairments.
They were found to be profoundly deaf and have disorders of the inner ear - of both the cochlea, which is responsible for hearing, and the vestibular system, which is responsible for balance.