Vestibular system

An equilibrium organ serves creatures on the perception of accelerations and to determine the direction of gravity. The stimulus is usually absorbed through sensory cells connected to one or - are coupled more specifically suspended or surface mounted solid state, so-called statoliths - as in humans. In the case of rotary motion is often used as a liquid in a tube system as inertial mass. In all vertebrates, including humans of the vestibular apparatus is the most important organ of equilibrium.

  • 5.1 The balance organs of the birds
  • 5.2 The balance organs of insects
  • 5.3 Other Animals

The vestibular apparatus in general

The paired vestibular organ (Organon vestibular, vestibular apparatus ) of vertebrates and the people located in the inner ear. It is divided usually into five components: three semicircular canals and the two structures called the saccule and utricle Maculaorgane. Fish and amphibians possess as an additional sixth part of a lagena, which is also a Maculaorgan. Even with the number of the semicircular canals, there are exceptions, but only in very original vertebrates. Lampreys have only two pairs of semicircular canals, hagfish even just a couple.

The vestibular apparatus of the human

The filled with endolymph semicircular canals form the body of rotation and are almost perpendicular to each other and so detect the rotational acceleration of the head in space. They consist of the actual bow, and out of an extension, the ampoule, respectively. In it are the hair cells of the semicircular canals, the sensory cells of the vestibular system. Their tips project into a gelatinous cone, the cupula. Upon rotation of the head, the endolymph flows because of their inertia against the direction of rotation by the semicircular canals. Thus, the cupula and lying in their sensory hair cells are bent and thus energized and an electrical signal passes through the archway nerve to the brain.

Saccule and utricle detect the translational acceleration of the body in space. Also perpendicular to each other so that the saccule and utricle responds to vertical to horizontal accelerations. The sensory cells project with their extensions ( sensory hairs, especially stereocilia ) in a gelatinous membrane containing otoliths. Otoliths are fine Kalziumkarbonatkristalle, which increase the density of the membrane and in turn allow an inertia effect, so that the detection of linear accelerations is at all possible.

From the sensory cells of the sensory information passes through the eighth cranial nerve ( vestibulocochlear nerve ) to the corresponding nerve nuclei in the brainstem ( vestibular nuclei ). This additional information from the eyes, from the cerebellum and the spinal cord.

The interconnection of the vestibular system with the eye muscles ( Vestibulookulärer Reflex) enables the visual perception of a stable image during simultaneous head movements.

For the conscious orientation in space next to the equilibrium system ( vestibular system ) and the visual system and the proprioceptive system ( proprioception ) are responsible.

If the function of these systems is disturbed, this may have conflicting information from the various sensory organs result. This can lead to dizziness. Dysfunction of the otoliths can cause benign positional vertigo.

Recent studies show that the organ of balance in the inner ear is responsible not only for the orientation in space: it plays a more important role in the precise control of body motions. Especially with movements in the dark or complex motion sequences as they run about Turner or artists, this function seems to play an important role.

Equilibrium test

Coordination tests

  • Romberg's test: The Examined stands with eyes closed so that the feet are touching the inside. The arms are stretched out horizontally. The examiner judged safe standing or falling tendency of the subject.
  • Unterberger - Tretversuch: The Examined marched with eyes closed " in one place ", possibly stretched his arms forward. The examiner assesses a tendency to fall sideways or backwards.
  • Accuracy: When walking with closed eyes to the front, the deviation is assessed.

Experimental tests

  • Caloric testing of the vestibular system: During the test, the patient lies with the head slightly elevated on the back. To ensure that no orientation in space is possible, should be closed his eyes. Flushing the ear canal with cold or warm water (30 ° C, 44 ° C) there is a movement of the endolymph in the vestibular organ that is connected with vertigo. In intact vestibular nystagmus can be, so watching a typical sideways twitching of the eye, and evaluate. In general, the eye moves in the hot flush in the direction of the stimulated ear, the cold stimulus in the opposite direction. If the eardrum is not intact, should not be rinsed with water. Alternatively, the test with diethyl ether or with air can be carried out.

The vestibular apparatus of fish and amphibians

In addition to the semicircular canals, all fish have three macular organs containing all depending a otoliths. This is especially the saccule the hearing, the density differences between Sagitta and the surrounding endolymph result in sound waves in the near field to shear movements on the hair cells. In order to expand the sense of hearing at greater distances and higher frequencies some teleost species possess special coupling mechanisms between their swim bladder and the skull bone or her inner ear. In a few cases, the inner ear is surrounded with special air-filled bubbles.

Also amphibians still have a lagena, but only the real accelerations. As far as we known, the saccule is used in these animals only in the performance of substrate vibrations, while the papilla amphibiorum also also can record sound and the basilar papilla exclusively serves the hearing.

Other organs of equilibrium

The vestibular organs of birds

Birds even have several independent organs of equilibrium. You have a second organ of equilibrium in lateral Auslappungen the spinal cord. It is solely responsible for the control of walking and standing. The vestibular apparatus in the inner ear, however, controls the movements of birds in flight.

The balance organs of insects

From insects a variety of organs has been described presumed or proven to serve as an organ of equilibrium:

  • The Grabersche organ in the abdomen of larvae brakes,
  • The Palmensche organ in the head of mayflies (static sense in larvae detected ) and
  • The Statozysten on 10th and 11th abdominal segment of larvae of a folding mosquito.

Other animals

Widespread in the animal kingdom are organs of equilibrium with a kinetically floating solids, a statoliths, which consists of the body's own material and is formed by biomineralization within the body or was taken from the outside. Such organs are usually referred to as Statozysten and found, for example at:

  • Ctenophora,
  • Planarians,
  • Molluscs,
  • Some annelids and
  • Some crustaceans.

Since the statoliths are in crayfish in pits at the base of the first sensor pair, they go after molting lost and must be replaced by the animals through a small stone from the area. This fact was the basis of experiments in which the crabs were asked after molting only ferrite grains available. The static meaning was thereby interfere with the aid of artificial magnetic fields and investigate targeted.

Supporting institutions

Allow the halteres of Diptera, determine velocity and accelerations in flight ( in a very different design but as a result a gyroscope accordingly).

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