Statolith
Statoliths, otoliths ("ear stones"), otoconia or statoconia are microscopic granules up to several centimeters in size made of solid material ( e.g. lime or starch) that are found in single cells as well as in the positional and equilibrium organs of many other living beings.
Due to their inert mass and their weight, they enable the organism to perceive accelerations (dynamic) and the direction of gravity (static). The term otolith refers on the one hand to the fact that these structures are located in vertebrates and humans in the inner ear , on the other hand they serve the hearing in many fish . Otoconia in the narrower sense is the term used to describe the biominerals in mammals that consist of calcium carbonate .
In multicellular cells, statolites can lie freely movable in statocysts (then they occupy the deepest point of space and press the sensory cells located at this point), or they can be attached to the hairs of sensory cells (and thus indicate the direction to the center of the earth) . Pressure, tensile and shear forces are perceived. The reflexes that are triggered by the heavy sense organs mean that the living being can maintain its normal position in space.
Mammals
In mammals, the structures utriculus (" small tube ") and sacculus ("sac") - two bulges of the membranous labyrinth - contain statoliths made of so-called auditory sand ( calcite crystals ) in a gel-like matrix of organic material in the inner ear . The stereocilia of the hair cells in the cave wall stick to these lumps of gel (otoconia) . Relative movements of the statoliths are transferred to the hairs and generate sensory stimuli.
As otoconia is called the essential, non-cellular components above the vestibular sensory cells of utricle and saccule in the balance organ of mammals. There they are embedded in a gelatinous mass (matrix) made of organic material. Otoconia belong to the biominerals, i. H. Structures made of inorganic material (minerals) and organic (biomolecules) that are formed in a self-organizing growth process by living organisms for special functions (e.g. equilibrium). Chemically, otoconia consist mainly of calcite, a stable modification of calcium carbonate, and organic components (<5%, e.g. glycoproteins and calcium-binding proteins).
In the nano range, human otoconia show structurally defined inorganic / organic subunits (nanocomposites) of different order (mosaic structure). Otoconia are therefore also characterized as mosaic-controlled nanocomposites. The inner structure consists of a dumbbell-shaped structure ("branches") that is dense in volume and nano-structurally ordered, which is surrounded by a less dense, nano-structurally less ordered outer structure ("belly").
fishes
In fish there are three otoliths on each side - a lapillus ("little stone") in the utriculus , a sagitta ("arrow") in the sacculus and an asteriscus ("asterisk") in the Lagena ("bottle" ) found in fish and amphibians ) named, third niche - usually only a few millimeters in size; however, they can also be a few centimeters long, for example the sagittae in the eagle fish . The otoliths each consist of aragonite or vaterite with a protein content (otolin) of 0.2 to 10 percent. Since they grow in layers, their onion-like structure can be used to determine their age. In cross-section they show annual rings (annuli) formed in areas with pronounced seasons. The number of years can be estimated on the basis of the number of changes between a light ring, usually a little wider, and a dark one, usually a little narrower - representing summer and winter.
In bony fish, the otoliths of the sacculus and the lagena mainly serve the sense of hearing and are therefore particularly large and sometimes connected to one another. The sagittae are often oval and laterally flattened. On the outside they usually have extensions, inside they are relatively smooth and have regular patterns. The latter even allow species to be determined (for example in the case of umberfishes, etc.) and, not least in the case of fossils , are of interest for questions about the evolution of bony fish.
plants
In plants, amyloplasts in statocytes , which are located in the root cap , in coleoptiles in the mesophyll and in sprouts in the extension zones of the growing internodes , represent statoliths. These help the plant to perceive gravity in order to adapt growth directions to gravity ( gravitropism ) . Roots usually grow towards the center of the earth, shoots in the opposite direction.
Artificial (biomimetic) otoconia
The working group around Kniep u. a. In 2008, the Max Planck Institute for Chemical Physics of Solids in Dresden succeeded for the first time in producing artificial ( biomimetic ) otoconia (calcite-gelatine composites) in vivo . On the basis of these studies, in which human and artificial otoconia were exposed to the drug gentamicin sulfate in vitro , it could be demonstrated that the basic morphological , chemical and physical properties of human and biomimetic otoconia are identical.
This assumption could also be confirmed by investigations of the dissolving behavior of human and artificial otoconia after exposure to gentamicin. Walther et al. a. were able to prove that artificial (biomimetic) otoconia are suitable as a model system to answer open questions such as B. structural changes to clarify how they z. B. as a result of degenerative changes ( benign paroxysmal positional vertigo ) or as a result of ototoxic drugs in otoconia.
Web links
Individual evidence
- ↑ P. Simon, W. Carrillo-Cabrera, YX Huang, J. Buder, H. Borrmann, R. Cardoso-Gil et al: Structural relationship between calcite-gelatine composites and biogenic (human) otoconia. In: Eur J Inorg Chem. 2011; 35, pp. 5370-5377.
- ↑ Leif Erik Walther, A. Blödow, MB Bloching, J. Buder, W. Carrillo-Cabrera, E. Roseeva and others. a .: The inner structure of human otoconia. In: Otol Neurotol. 35, 2014, pp. 686-694.
- ↑ Arthur N. Popper: Organization of the inner ear and auditory processing. In: R. Glenn Northcutt, Roger E. Davis (Eds.): Fish Neurobiology. Volume 1: Brain stem and sense organs. University of Michigan Press, Ann Arbor MI 1983, ISBN 0-472-10005-X , pp. 126-178.
- ↑ A. Bresinsky among others: Strasburger - Textbook of Botany. 36th edition. Springer Spectrum, Berlin / Heidelberg 2008, ISBN 978-3-8274-1455-7 .
- ↑ YX Huang, J. Buder, R. Cardoso-Gil, Y. Prots, W. Carrillo-Cabrera, P. Simon u. a .: Shape development and structure of a complex (otoconia-like?) calcite-gelatine composite. In: Angew Chem Int Ed Engl. 2008; 47, pp. 8280-8284.
- ↑ Leif Erik Walther u. a .: Gentamicin-induced structural damage of human and artificial (biomimetic) otoconia. In: Acta Otolaryngol. 134 (2), 2014, pp. 111-117.