Organ of Corti

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Section through the cochlea: structure of the organ of Corti.
Contrary to the drawing, the stereovilli of the inner hair cells have no contact with the tectorial membrane, and of the stereovilli of the outer only the longest.

The organ of Corti ( Corti's organ after the Italian anatomist Alfonso Corti , Latin Organon spirale ) is the name of the interface in the cochlea of the inner ear between the acoustic mechanical vibrations and the nerve signals .

construction

The organ of Corti is the carrier of the sensor cells in the inner ear of all mammals. It also contains supporting cells that surround the sensory cells.

It is separated from the Scala tympani by the basilar membrane . On the other hand, the human organ has three rows of outer and one row of inner hair cells (hearing sensor cells). Their “cell hairs” ( stereovilli ) protrude into a gap that is connected to the scala media and is filled with endolymph . A cell can have up to a hundred stereovilli. The tectorial membrane , a gelatinous mass, is located above the gap (in the scala media) . The longest stereovilli of the outer hair cells are in contact with the tectorial membrane. The deflection of the stereovilli of the inner hair cells triggers the stimulus transduction and thus the hearing sensation. In contrast to the hair cells of the organ of equilibrium , the hair cells of the cochlea do not have kinocilia .

The supporting cells are divided into outer and inner pillar and phalangeal cells. The outer and inner pillar cells form a triangular canal, the Corti tunnel ( Cuniculus internus ). The phalangeal cells stand in two to five rows and take up the hair cells. The outer pillar cells are separated from the outer phalangeal cells by the Nuel space. The outer phalangeal cells are followed by the Hens and Claudius cells. The latter merge into the stria vascularis .

Sound sensation

A sound wave is transmitted via the eardrum and the ossicles in the middle ear to the scala vestibuli , which, like the scala tympani , is filled with perilymph . The pressure wave in the scala vestibuli leads to the deflection of the Reissner membrane, the scala media and the entire organ of Corti towards the scala tympani. This leads to a shear movement of the tectorial membrane against the hair cells: The stereovilli of the outer hair cells are bent and these cells are excited. Most stereovilli are connected to the villus behind them by so-called 'tip links' so that they are deflected together. As a result of the displacement, cation channels in the hair cell directed towards the endolymph open or close .

The potassium - ion concentration is in the endolymph and in the hair cells of approximately the same height. The endolymph, however, is positively charged with around 85  mV , whereas the hair cells have a negative resting membrane potential of around −70 mV. With open potassium channels, the positively charged potassium ions therefore flow into the hair cells.

The resulting depolarization of the cell membrane leads to an oscillating change in length in the outer hair cells, which is transferred to the basilar membrane. Speeds of up to 20,000 oscillations per second can be achieved. For a given pitch, such amplification occurs only at one point on the cochlea. Only here is there a massive increase in the flow of the endolymph under the tectorial membrane. This also stimulates the inner hair cells at this point. This local limitation of the excitation amplification allows a distinction between different pitches (see also cochlear amplifier and traveling wave ).

The inner hair cells are also depolarized. This leads to the release of the neurotransmitter glutamate at the lower end of the cells . It diffuses through the synaptic gap to the neighboring nerve cell and leads to the formation of action potentials , which electrically pass the information on to the brain via the sound heard . This is done via the auditory nerve .

The repolarization of the hair cells takes place via potassium-specific channels on the lateral cell membrane.

See also

literature

Individual evidence

  1. ↑ Hans-Georg Liebich: Functional histology of domestic mammals: textbook and color atlas for study and practice . Schattauer Verlag, 2004, ISBN 9783794523115 , p. 358.