Balance organ

The Balance organ, also Vestibular apparatus, is located in pairs in the right and left inner ear. The three semicircular canals, which are perpendicular to one another, report rotational accelerations, and the otolith organs (sacculus and utriculus) react to translational accelerations. Due to the physical mode of action, there may be brief disorientation after an acceleration or braking phase.

What is the organ of equilibrium?

The organ of equilibrium in its entirety, or better, the vestibular apparatus, consists of several organs of equilibrium in the inner ear. For the reporting of rotational accelerations, a semicircular canal is available for the pitch, roll and vertical axes. The three semicircular canals are perpendicular to each other.

The two otolith or macular organs sacculus and utricle are used to record and report linear (translational) accelerations. Although there are only two organs, linear accelerations can be detected in the three possible directions up / down, right / left and forwards / backwards. The sensory system of all equilibrium organs is based on the inertia of the endolymph in the semicircular canals and tiny calcium carbonate crystals (otoliths) in the macular organs.

The function of the balance organs is very important for the sense of balance, but is not exclusively responsible for balance. The sense of sight has a complementary - and partially corrective - effect. The sense of balance is enhanced by thousands of proprioceptors, which contribute information about muscle tension and the flexion angle of the individual joints.

Anatomy & structure

The three semicircular canals, filled with endolymph, consist of small semicircular tubes that are connected to each other at the base. Each semicircular canal thickens in the lower area to form an ampoule, into which fine sensory hairs (mechanoreceptors) reach. In the event of a rotational acceleration in the plane of the corresponding semicircular canal, the endolymph remains briefly in the initial position due to the inertia, so that it moves against the rotational acceleration.

As a result, the sensory hairs in the ampoule are deflected and generate an electrical stimulus that is reported to certain areas of the brain and the visual center via the vestibulocochlear nerve. A gelatinous membrane in the two macular organs contains tiny calcium carbonate crystal grains (otoliths or statolites).

In the case of a linear acceleration, the statolith membrane is briefly deflected in the direction opposite to the acceleration due to the inertia of the tiny crystals. The sensory hairs protruding into the macular membrane bend and generate an electrical stimulus, which is also transmitted by the vestibulocochlear nerve.

Function & tasks

The task of the vestibular organs is to transmit rotational and linear accelerations to certain areas of the brain. Rotational accelerations or decelerations in the tilt, roll or vertical axis are reported from one semicircular canal each.

The utriculus perceives linear accelerations in the two horizontal directions “front / back” and “right / left” and the utriculus reacts to vertical acceleration. In an upright position, the saccule's sensory hairs are constantly slightly deflected due to gravity, which represents a vertical linear acceleration towards the center of the earth. This creates a feeling for the position of the body in space, which is extremely helpful for orientation in the dark and enables walking or standing without sight.

Even movements are the result of previous accelerations, but are not perceived by the mechanoreceptors because they are not bent. Decelerations of a linear or rotary movement are perceived as acceleration in the respective opposite direction. In addition to the support for orientation in space, the reported accelerations have a direct effect on involuntary eye movements.

Every perceived rotational or linear acceleration causes an involuntary reflex-like eye movement in the opposite direction in order to be able to keep the natural environment in view. The eyes are stabilized, so to speak, when walking, running and jumping, so that we can continue to see the surroundings in focus despite acceleration without “blurring” (comparable to a gyro-stabilized camera).

Illnesses & ailments

If the perceived accelerations do not correspond to the vision, the different sensations cause a sensor conflict (imbalance). In these cases, the vision always acts as the “master”, the vestibular sense of acceleration is manipulated and adapted to the vision.

This can be very helpful in cases in which vestibular false reports occur briefly (1 to 3 seconds). If the discrepancies persist, you may feel unwell, dizzy, or nauseous and even vomit. Similar symptoms can also be caused by disorders and diseases in the inner ear on the vestibular organs. Temporary disorders can be caused by inflammatory processes in the inner ear or by injuries such as the base of the skull fracture. After healing, the symptoms will go away on their own.

Unpleasant dizziness can have a variety of causes and can appear as a side effect of circulatory disorders or be caused by nervous damage or special psychological exceptional states. In the case of persistent and recurring attacks of vertigo, Menière's disease can be the cause. It is a metabolic disorder of the inner ear, the cause of which is not adequately understood. Since direct causal treatment is not possible, drug therapies and treatments aim to alleviate symptoms.