Organ of Corti: characteristics of this part of the inner ear

Our ability to perceive what is happening around us is a key element in allowing us to survive. Of all the senses, the most developed in the human being is that of sight. But probably after this the next one that seems most relevant to us when it comes to analyzing the environment is that of the ear.

Thanks to hearing we are able to perceive the vibrations generated by elements as relevant as the movements of the stimuli or our distance from them. And it even allows us to generate and capture speech, or enjoy music. But for this we need something that transforms the vibrations into something actionable. And within the auditory system, there is a fundamental organ in this process: the organ of Corti.

• Related article: "Parts of the human brain (and functions)"

The organ of Corti: an important part of the auditory system

It receives the name of organ of Corti a small structure present in our auditory system which is of paramount importance for said system, since it is the one in charge of taking the first step in the transformation of environmental vibrations in stimuli interpretable by our nervous system and without it we would not be able to perceive auditory.

This spiral-shaped organ is part of the inner ear and is part of the auditory neuroepithelium. It is located in the cochlea, specifically in the middle ramp of this one, supported on the basilar membrane.

The organ of Corti is a sensory structure in which various types of cells are found along four large rows, mainly ciliated, that possess mechanoreceptors and which connect with the auditory nerve (the bodies of the neurons of the VIII cranial nerve are found in the organ of Corti).

These cells, which are found in large numbers (between 16,000 and 24,000), are the main receiver of the sounds that reach us.

The relevant role of this body: how do we hear?

The organ of Corti is perhaps one of the most important in the auditory system, and it is thanks to it that our body is capable of transducing external stimuli.

To better understand its operation, we must bear in mind that the sounds we perceive are waves of different frequencies, which generate a vibration when emitted. But our nervous system does not work with these waves without more: it is necessary that there be some organ or element that receives this information, of a mechanical nature, and transforms it into a bioelectric impulse that can travel and be interpreted by the brain. And in this case this receptor is the organ of Corti, or rather the hair cells that are part of it.

When we hear something we are actually picking up vibrations, which reach our auditory system through the auditory pin and travel by the different parts of the outer and middle ear: the auditory canal, the eardrum and the chain of ossicles (anvil, hammer and stapes), as well as well as the Eustachian tube, up to the oval window, a membrane that covers the cochlea and from which the ear begins internal.

In the cochlea there are different parts, one of them being the basilar membrane. The vibrations that arrive will generate a wave that will cause a movement of the cells that rest on it., which are those that are part of the organ of Corti, in such a way that this movement causes them to open ion channels that will end up generating a depolarization, turning the mechanical wave into a signal bioelectric.

In addition to the mere perception of sound, according to the tonotopic theory, thanks to the organ of Corti we can also differentiate between different tones and volumes, depending on the area in which the movement of the basilar membrane generates the maximum stimulation of the cells ciliated. Likewise, from the observation of cases in which there is damage in this area and in the cochlea, it has been observed that there is a relationship between the organ of Corti and equilibrium.

Two major types of hair cells

As we have commented, the organ of Corti consists of a series of cells which allow us to transform vibrations into sounds. The main cells responsible for this phenomenon are the ciliates.. Now, not all cells of the organ of Corti are the same, but we can find two types of them.

Inner hair cells

The inner hair cells (we have approximately 3,500) are properly the phono-receptors of the auditory system, that is, those elements that generate the transduction of information from vibration to impulse electric.

These are cells that are supported by the basilar membrane and that are connected to the auditory nerve, and whose action occurs when its movement causes the displacement of the liquid in which they are immersed or endolymph.

This generates a movement of the cilia, that open channels through which sodium and potassium ions enter in such a way that they end up causing a depolarization, in which they will release glutamate in neurons that innervate them and generate that they are generate the electrical impulse and take it to the central nervous system.

Outer hair cells

The outer hair cells (around 12,000) differ from the previous ones in that, in fact, they are attached to the membrane tentoria by their longer cilia, while they are in contact with the basilar from other cells that give them medium, Deiters cells. The external ciliates are totally affected by the movement of the basilar membrane, independent of the movement of the endolymph.

Its function does not go through generating electrical stimuli from mechanical stimuli so that the brain can process them, but rather they do the opposite in order to be able to modulate the selectivity of the frequencies we pick up. They are mainly modulators.

Support cells

Although the ciliates are the most relevant cells to explain the functioning of the organ of Corti, it is necessary mention that in addition to them within said organ we can find cells that provide support and allow survival of this. These are, for example, the aforementioned Deiters and Hansen cells (which are attached to them).

Problems related to injuries to this organ

The organ of Corti and the cochlea are fundamental elements in the perception of soundTherefore, the existence of diseases or injuries that alter their operation or destroy them will have serious consequences in this regard. The causes that can generate this type of injury can be found in trauma, tumors, infections, aging of the auditory system or irrigation problems.

The degeneration or injury of the organ of Corti can cause alterations such as the presence of tinnitus, echoes, hearing loss or sensorineural hearing loss, algiacusis (pain in hearing) or even diploacúsias (double perception of the same sound, even within the same ear).

The complete loss of this organ would cause deafness, since we would not be able to process the auditory information. Also disturbances in balance.

Bibliographic references:

• Tresguerres, J.A.F., Ariznavarreta, C., Cachofeiro, V., Cardinali, D., Escrich, E., Gil, P., Lahera, V., Mora, F., Romano, M., Tamargo, J. (2005). Human physiology. 3rd Edition. McGraw Hill.