Synonyms
Vestibular apparatus, vestibularis organ, vestibular organ, vestibular balance ability, movement coordination, dizziness, vestibular organ failure
Definition
Balance in the sense of the ability to balance is defined as the ability to keep the body and/or parts of the body in balance, or to bring them back into balance during movements. The organ of equilibrium is used to measure linear acceleration and rotational acceleration. The maculae are responsible for measuring linear acceleration and for registering deviations of the head from the vertical.
This works with the help of the statolith membrane, because the statoliths have a higher inertia compared to the surrounding endolymph. As a result, the endolymph is deflected with the cilia of the hair cells during movements, but the statolith membrane remains behind. This deflection of the cilia causes them to be excited by opening ion channels (sodium, potassium, calcium) and in this way a nerve impulse can be generated and transmitted to the brain.
The cristae of the archways take over the registration of the rotational acceleration. Again, inertia plays a role as a measuring mechanism. The cupula behaves less inertially than the endolymph surrounding it.
When the head rotates, the inertia of the endolymph in the semicircular canals causes it to lag behind the cupula, resulting in relative movement with deflection of the cilia of the sensory cells. This stimulus triggers the same transmission mechanism as already described for the maculae. Ultimately, the measurement of these accelerations is used to offset them against other information so that, on the one hand, equilibrium can be maintained and, on the other hand, an object can be fixed during head movements and thus a constant optical impression can be obtained.
The latter is called the vestibulo-ocular reflex, which is used for spatial orientation. This requires the interaction of eye muscles for compensatory eye movements, of neck muscles for compensatory neck position changes, and of the organ of equilibrium. The whole enables the interconnection of the individual components in the central nervous system (brain, brain stem, spinal cord) as described above.
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