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

A summary of the characteristics of this organ, which enables the process of hearing.

Our ability to perceive what is going on around us is a key element in enabling us to survive. Of all the senses, the most developed in humans is sight. But probably after this one, the next most relevant one when it comes to analyzing the environment is hearing.

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

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

It is called the organ of Corti a small structure present in our auditory system It is the first step in the transformation of environmental vibrations into stimuli that can be interpreted by our nervous system and without it, auditory perception would not be possible.

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

The organ of Corti is a sensory structure in which along four large rows there are various types of cells, mainly hair cells, which have mechanoreceptors and which are connected to the auditory nerve (the bodies of the neurons of cranial nerve VIII are located in the organ of Corti).

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

The important role of this organ: how do we hear?

The organ of Corti is perhaps one of the most important organs of the auditory system, and it is thanks to it that our organism is able to transduce external stimuli.

To better understand how it works, we must bear in mind that the sounds we perceive are waves of different frequencies, which generate a vibration when they are emitted. But our nervous system does not work with these waves: there must be some organ or element that receives this information, of a mechanical type, and transforms it into a bioelectrical impulse that can travel and be interpreted by the encephalon. into a bioelectrical 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 pinna and travel through the different parts of the external and middle ear: the auditory canal, the eardrum and the chain of ossicles (anvil, hammer and stirrup), as well as the Eustachian tube, until they reach the oval window, a membrane that covers the cochlea and from which the inner ear begins.

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 part of the organ of Corti.This movement causes the opening of ion channels that will eventually generate a depolarization, turning the mechanical wave into a bioelectrical signal.

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 hair cells. Likewise, from the observation of cases in which there is damage in this area and in the cochlea, it has been possible to observe that there is a relationship between the organ of Corti and balance..

Two major types of hair cells

As we have already mentioned, 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 hair cells.. However, not all the cells of the organ of Corti are the same, but we can find two types of them.

Inner hair cells

Inner hair cells (approximately 3500) are the phonoreceptors of the auditory system, i.e. those elements that generate the transduction of vibration information into an electrical impulse.

They are cells that are supported by the basilar membrane and are connected to the auditory nerve. are connected to the auditory nerveTheir action is produced when the movement of the latter causes the displacement of the liquid in which they are immersed or endolymph.

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

Outer hair cells

The outer hair cells (about 12,000) differ from the previous ones in that they are actually attached to the tentorial membrane by their longer cilia, while they are in contact with the basilar from other cells that support them, Deiters cells. The outer hair cells are totally affected by the movement of the basilar membrane, independently of the movement of the endolymph.

Their function is not to generate electrical stimuli from mechanical stimuli so that the brain can process them, but rather to do the opposite in order to be able to modulate the selectivity of the frequencies that the brain processes. modulate the selectivity of the frequencies we pick up.. They are mainly modulators.

Support cells

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

Problems related to lesions in this organ

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

Degeneration or lesion of the organ of Corti can lead to alterations such as the presence of tinnitus, echoes, hearing loss or sensorineural hearing loss, algiacusia (pain in hearing) or even diploacusis (double perception of the same sound, even within the same ear). (pain in hearing) or even diploacusis (double perception of the same sound, even within the same ear).

The complete loss of this organ would cause deafness, as we would no longer be able to hear.The complete loss of this organ would cause deafness, since we would not be able to process the auditory information. Also alterations in balance.

Bibliographical 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.