Cochlea: anatomy, function, and related pathalogies

Q: Damaged hair cells

The organ of Corti contains about 20,000 hair cells, which, if damaged, can lead to sensorineural hearing loss, the most common form of hearing loss in humans. This damage to the hair cells in the ear is usually due to excessive exposure to loud noises. Once these cells are damaged, the function of the cochlea is permanently impaired because the hair cells are unable to regenerate.

Q: Malformations of the inner ear

Malformations of the inner ear can include cochlear aplasia, which indicates the complete absence of the cochlea. Pendred syndrome, on the other hand, is a rare genetic disorder characterised by early deafness. People with this syndrome, unlike those with cochlear aplasia, can use cochlear implants, which are applied through surgery.

The cochlea: a part of the inner ear

The cochlea is the part of the inner ear that translates acoustic information into nerve impulses comprehensible to the human brain, thus enabling the perception of sounds. The cochlea has a spiral-shaped hollow structure. If it is damaged, the cochlea can permanently lose its function, and the person who has suffered this damage develops a type of deafness called sensorineural hearing loss.

Definition

Let's start with the definition of cochlea, a word derived from the ancient Greek “kōhlias” meaning spiral. In fact, the cochlea is also known as the snail because of its characteristic shape. It is the structure that, together with the vestibular apparatus, makes up the membranous labyrinth. The cochlea performs a very important function because it translates acoustic information into nerve impulses through the organ of Corti, a structure inside the cochlea.

Anatomy

The cochlea has a spiral-shaped cavity structure and consists of three different districts placed one above the other, which are called the scala or ducts: the scala vestibuli, the scala media and the tympanic scala.

The scala vestibuli is the upper district of the cochlea, and within it writes perilymph, an extracellular fluid essential for the perception of sounds.
The scala media is the district located in the middle and within it are two very important elements for the perception of sounds: the organ of Corti and the endolymph.
The tympanic scale, on the other hand, is the lower district of the cochlea and within it circulates the perilymph.

Function

The cochlea performs an important function, which is to transform mechano-vibratory acoustic information into a nerve impulse so that the brain is able to interpret it. The cochlea begins to do its work when it is stimulated by sound waves that create the displacement of the perilymph contained in the vestibuli and tympanic scales. Through this action, the perilymph is able to move the membrane of the organ of Corti and stimulate its constituent hair cells. Subsequently, the acoustic information is transformed into a nerve impulse and is sent to the brain via the cochlear nerve.

A woman with her left hand resting on the headphones during a hearing test

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Cochlea abnormalities and pathologies

In case of abnormalities or pathologies of the cochlea, hearing problems may occur. The cochlea may be damaged, for example, at the level of the hair cells that form the organ of Corti. The use of certain drugs, such as neomycin, can also have adverse effects on the cochlea and hair structures. Then, there are congenital malformations of the inner ear that lead to hearing loss. Let's see what are the abnormalities and pathologies of the cochlea.

Damaged hair cells

The organ of Corti contains about 20,000 hair cells, which, if damaged, can lead to sensorineural hearing loss, the most common form of hearing loss in humans. This damage to the hair cells in the ear is usually due to excessive exposure to loud noises. Once these cells are damaged, the function of the cochlea is permanently impaired because the hair cells are unable to regenerate.

Drug-induced ototoxicity: neomycin

Hair cells can also be damaged by the use of certain drugs, such as neomycin, which is the antibiotic with the greatest cochleotoxic effect. This drug causes temporary ' ototoxicity due to accumulation of the drug in the inner ear cells. The effects regress when you stop taking this medicine. The moment drugs with ototoxic characteristics are taken for prolonged lengths of time, the hair cells are irreversibly damaged.

Meniere's disease

Ménière syndrome is an inner ear disorder that causes vertigo, fluctuating sensorineural hearing loss, full ear sensation, and tinnitus. For the treatment of this problem, anticholinergics or benzodiazepines are used in the acute phase. For more severe cases, however, surgery may be necessary.

Malformations of the inner ear

Malformations of the inner ear can include cochlear aplasia, which indicates the complete absence of the cochlea. Pendred syndrome, on the other hand, is a rare genetic disorder characterised by early deafness. People with this syndrome, unlike those with cochlear aplasia, can use cochlear implants, which are applied through surgery.

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Cochlea and hearing loss

Some people may suffer from a partial or complete inability to perceive sound from one or both ears. This problem is called hearing loss and can be genetic or develop over the years or as a result of illness and trauma. There are symptoms that enable hearing loss to be recognised, such as perception of muffled sounds, difficulty understanding words in noisy situations, difficulty following television and also experience dizziness and ringing in the ears.

Cochlear implants

In order to solve problems related to hearing loss, where hearing aids are not sufficient, a viable solution is cochlear implants. A cochlear implant is a highly advanced electronic device that can pick up sounds in the environment and convert them into electrical impulses that are sent directly to the auditory nerve. These implants can be applied to both children and adults through surgery.

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