Vestibular system

(redirected from Vestibular organs)
Also found in: Dictionary, Thesaurus, Medical.
Related to Vestibular organs: vestibular nerve, Bipolar cells

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.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
Mentioned in ?
References in periodicals archive ?
At E13.5, Pax2 was mainly located in the nonsensory domains of the vestibular organ and the cochlea.
Expression of Pax2 in the utricle, saccule, and three cristae of the vestibular organ differed from the expression in the organ of Corti.
With a sudden pathological dysfunction of one vestibular organ (mostly hypofunction), the two sides discharge at unequal rates.
The brain scans revealed differences between the groups in two parts of the brain: an area in the cerebellum where sensory input from the vestibular organs is processed and in the cerebral cortex, which is responsible for the perception of dizziness.
Some research has shown that there are certain variations in the pattern of venous drainage of the vestibular organs. Mazzoni demonstrated that in a certain percentage of human temporal bones, one or two of the vestibular veins drain through the VPVC rather than serving as tributaries of the inferior cochlear vein.
(4) After they surgically lowered the jugular bulb, the symptoms improved, thus adding credence to the importance of venous drainage of the vestibular organs through the VPVC.
This leads to failure of the cochlea and the vestibular organs, resulting in deafness and loss of balance.
Sensory hair fusion and glycocalyx changes following gentamicin exposure in the guinea pig vestibular organs. Acta Otolaryngol 1989;107:39-47.

Full browser ?