Balance organ

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The organ of equilibrium (vestibular apparatus) provides us with information about accelerations in the three spatial levels (upwards, downwards, to the side) and about linear accelerations (increase or decrease in speeds). In addition, special sensory cells in the inner ear (labyrinth / ear) register sensations of equilibrium. Read everything you need to know about the organ of equilibrium!

What is the organ of equilibrium?

The sense of balance comes about through the interaction of the balance organ in the inner ear with the eyes and the central processing of information in the brain.

The organ of equilibrium (ear) consists of two different systems:

• The static system responds to linear motion and gravity.
• The semicircular canal system registers rotational movements.

Both systems are located in the inner ear in the petrous pyramid, in the membranous labyrinth that is filled with endolymph - a fluid whose composition roughly corresponds to the fluid inside a cell.

static system

The static system of the organ of equilibrium consists of two vesicles filled with endolymph (sacculus and utriculus), which lie behind the oval window in the inner ear and are connected to one another. Both have a thickened sensory field with sensory cells in a special area, the macular organ. The macula of the utricle is horizontal, that of the saccule is vertical. The hairs of the sensory cells protrude into a jelly-like membrane in which fine lime crystals are embedded - the so-called ear stones (otoliths).

The function of the macular organ

Since the lime crystals have a higher specific gravity than the endolymph, they follow gravity and, when we stand upright and hold our head straight, press on the sensory hairs of the macula of the utricle, which are horizontal. They pull on the sensory hairs of the macula of the saccule, which are vertical. This creates the sensation of an upright, regular body position - the sense of balance (ear).

When the position of the head changes, the lime crystals, which always follow gravity, pull on the higher side and press on the lower side - this creates a feeling from above and below. The vestibular apparatus also gives a feeling of rising and falling - for example when using a lift - because the macular organ of the utriculus is more stressed when traveling upwards and is relieved again when traveling downwards.

These changes in state are passed on to the central nervous system, which then, as a reflex, corrects the state of tension (tone) of the skeletal muscles in an appropriate manner. The aim is always to keep the body upright to prevent falling.

Semicircular canals

The semicircular canals of the organ of equilibrium are closely connected to the utriculus. There are three arcades lying in the three spatial levels and perpendicular to one another - one horizontal, one frontal and one vertical. Each of the three semicircular canals forms a ring-shaped tube that arises from the utriculus and also ends there again. One end of each semicircular canal is widened, and in this widening there is a ledge at right angles to the axis, which carries support and sensory cells on the surface. The sensory cells have hairs that protrude into a jelly-like mass (cupula).

When the cupula moves even slightly, the sensory cells respond. Depending on the movement of the head in the plane of one of the three semicircular canals, the endolymph initially stops because of its inertia and thus also holds the cupula. The bony base of the semicircular canal continues to move, which mechanically stimulates the sensory cells. These stimuli are converted into excitations of the nerves and passed on to the brain. In order to maintain a stable posture / posture, the corresponding muscle groups are activated or deactivated again.

Adaptation to various changes in position

The work of the organ of equilibrium - the constant orientation in three-dimensional space - is very important in order to be able to adapt quickly to changed postures. Through the interaction of both systems of the organ of equilibrium (with five sensory endpoints each - the two macular organs and the three semicircular canals), the position and movements of the head can be determined very precisely.

The sensory cells in the organ of equilibrium are in a permanent state of excitement, so send signals to the brain even in the resting state, which are increased or inhibited accordingly during movements. Since the upright gait is important for humans, this system of rapid information from the organ of equilibrium is of great importance.

What problems can the organ of equilibrium cause?

The most common symptom of disorders of the balance organ is dizziness associated with nystagmus (eye tremors).

If a system of the organ of equilibrium becomes ill (inflammation, tumor, Menière's disease, etc.) or suddenly fails, the information on the healthy side becomes overweight. The consequences are vestibular nystagmus (eye tremors) and vestibular dizziness.

A change in the position of the head can trigger so-called positional vertigo, especially in older people. The cause is an otolith that enters the semicircular canals from the macular organs. In addition to old age, this can also happen in the event of an accident, for example.

In the case of motion sickness or seasickness, various information about the position of the body reaches the brain from the equilibrium organ, which causes dizziness and nausea.

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