Organ of Corti - The Human Ear Cochlea

Introduction

The organ of Corti is present in the inner ear within the cochlea (snail-shaped organ present in the inner ear). The organ of Corti was named after Alfonso Corti, who first described this organ in 1851. The organ of Corti consists of outer hair cells (three rows) and inner hair cells (one row). These hair cells in the organ of Corti usually bend in response to vibration produced by the sound waves and convert these mechanical signals into electrical signals, which are further transmitted to the brain to perceive the sound by the auditory nerve to facilitate the hearing mechanism.

What Is the Anatomy of the Organ of Corti?

The spiral organ or organ of Corti comprises four layers of sensory hair cells out of which three layers are present in the outer ear and one layer in the inner ear. The inner ear hair cells are attached to the cochlear nerve that transfers the sensory signals to the brain.

What Are the Histological Features of the Organ of Corti?

The organ of Corti comprises three cells:

• Inner Hair Cells: It comprises 3500 cells in the basilar membrane. It helps in the conversion of mechanical signals to electrical signals, which are transferred to the brain for perceiving sound through the auditory nerve.

• Outer Hair Cells: It comprises 12000 cells that are connected to type two myelinic neurons.

• Supporting Cells: The organ of Corti comprises four types of supporting cells:

1. Corti pillars.

2. Hensen cells.

3. Claudius cells.

4. Deiters cells.

What Is the Function of the Organ of Corti?

The functions of the organ of Corti are:

• Transfer of Sound Signals: The organ of Corti helps in the transduction of auditory signals by conversion of mechanical signals into electrical signals, which are further transferred to the brain for sound perception.

• Electrochemical Impulse Regulation: The cochlear duct comprises endolymph which is secreted by the stria vascularis. The endolymph consists of potassium ions at high concentrations. The endolymph helps in the regulation of impulses of the auditory hair cells. Endolymph consists of different ions like:

1. Sodium.

2. Potassium.

3. Chloride.

How Does the Mechanism of Transduction Occur?

The organ of Corti helps in the transduction mechanism (conversion of sound signals to electrical signals) by converting the pressure waves produced by perilymph and endolymph to electrical signals. The transduction mechanism occurs in the following steps:

• Deflection: In this step, the opening of potassium (K+) channels occurs, resulting in the entry of potassium into the cells.

• Depolarization: This step consists of the entry of the calcium ions into the cells based on their voltage-dependent channels.

• Potassium Extrusion: Higher concentration of calcium ions within the cells results in the extrusion (outward) of potassium ions and release of glutamate in the synaptic cleft (space between the neurons and axon terminals of the nerve).

• Generation of Action Potential: This step is characterized by the generation of the action potential along the hearing or the auditory nerve (the eighth cranial nerve).

What Is the Blood Supply of the Organ of Corti?

The organ of Corti is supplied by the labyrinthine artery, also known as the internal auditory artery. Anterior inferior cerebellar artery originates from the basilar artery and gives a branch of an internal auditory artery that supplies the organ of Corti. In a few people, the internal auditory artery directly arises from the basilar artery (15 percent of cases). The labyrinthine artery divides further into two branches that are the common cochlear artery and the anterior vestibular artery in the internal acoustic meatus. The common cochlear artery is further branched into the vestibulocochlear artery and proper cochlear artery.

What Is the Nerve Supply of the Organ of Corti?

The organ of Corti is supplied by the eighth cranial nerve, also called the vestibulocochlear nerve.

What Is the Clinical Significance of the Organ of Corti?

Any damage to the organ of the Corti results in sensorineural hearing loss or permanent deafness.

What Can Cause Damage to the Organ of the Corti?

The organ of the Corti can be damaged due to the following:

• Infections: Inner or middle ear infections can result in damage to the organ of the Corti leading to sensorineural hearing loss.

• Adverse Effects of Ototoxic Drugs: Continuous exposure to ototoxic drugs (drugs that are toxic to the ears) like Aminoglycosides can result in failure of depolarization of outer and inner hair cells. The aminoglycosides block the potassium channel and thereby block the depolarization process. The repetitive exposure to ototoxic drugs results in the inner hair cells being damaged, leading to hearing loss.

• Exposure to Loud Noise: Continuous exposure to loud noise results in damage to the stereocilia (finger-like projections) of the outer hair cells, which leads to the loss of stiffness of the organ of Corti. This loss of stiffness results in an increase in the vibrational forces within the inner ear resulting in hearing loss.

How Can We Diagnose the Damage to the Organ of the Corti?

The diagnosis of any damage to the organ of the Corti can be made by the following:

• History and Clinical Examination: A detailed history of the patient for the presence of the symptoms like ear fullness, reduced hearing abilities, drug history to rule out ototoxic drug exposure, and any continuous exposure to loud noises is noted. A clinical examination of the ears is done by an ENT (ear, nose, and throat) specialist to rule out any ear infections present.

• Computed Tomographic (CT) Scan: These scans are done for the temporal bone to rule out any defects or abnormalities in the middle and inner ear.

• Pure Tone Audiometry Test: The hearing test is done to rule out the severity and type of hearing loss present in patients with suspected hearing loss.

What Are the Complications Associated With Surgical Electrode Array Placement in Cochlea and Its Failure?

The electrode array of a cochlear implant (an artificial hearing device) is a very risky and crucial step during the placement of a cochlear implant. The complications associated with surgical technique and electrode array device failure are:

• Infections.

• Damage to the middle and inner ear.

• Tinnitus (ringing sensation in the ears).

• Failure of device.

• Mastoiditis (infections and inflammation of mastoid air cells).

Conclusion

The organ of Corti is present within the cochlea in the inner ear. Any damage, infections, and toxicity associated with the inner ear can lead to damage to organs of the Corti resulting in complications like permanent hearing loss. Early diagnosis and treatment of cochlear abnormalities are crucial to prevent the associated complications.