The caloric test checks the function of the horizontal semicircular canals by stimulating the auditory canal with warm or cold water or air. The temperature difference creates a convection of the endolymph, which causes nystagmus (uncontrollable eye movements) and thus visualizes the vestibular function. The strength and direction of the nystagmus provide an indication of the integrity of the vestibular system and its central circuitry. This procedure is particularly important for diagnosing unilateral vestibular deficits and for clarifying symptoms of vertigo. Side effects are rare, but may increase nausea or dizziness in the short term.

The semicircular canal is a bony canal filled with endolymph in the inner ear that registers rotational movements of the head. Each of the three orthogonally arranged canals (horizontal, superior, posterior) contains a sensor capsule (ampulla) with hair cells that are mechanically stimulated by the flow of fluid. These stimuli are transmitted to the brain via the vestibular part of the VIII. These stimuli are transmitted to the brain via the vestibular part of the VIII cranial nerve and are essential for balance and spatial orientation. Disturbances or blockages in the semicircular canals, as occur in benign paroxysmal positional vertigo, lead to severe dizzy spells. Caloric testing and video nystagmography are standard methods for testing their function.

The capitis transversus muscle, also part of the deep neck muscle, attaches to the mastoid process and stabilizes head movements. Its tension can indirectly influence the pressure in the middle ear, as the skull bone transmits slight deformations. Tension in this muscle in the postauricular region is occasionally associated with earache and tinnitus. Manual therapy and physiotherapeutic stretching exercises release muscular imbalances and alleviate accompanying symptoms. During the clinical examination, the therapist looks for pain radiating towards the ear.

A cartilaginous earmold is an individual earmould made of flexible material that is inserted into the ear canal and seals hearing aid components tightly. It optimally transmits sound to the inner device and prevents feedback. Thanks to its soft texture, it adapts to the shape of the ear and offers long hours of wearing comfort. Hygienic cleaning and regular replacement are important to prevent earwax build-up and skin irritation. Custom-fit adapters significantly improve sound quality and speech intelligibility.

Cerebral hearing loss results from damage to the central auditory pathways or auditory cortex, but not from problems in the ear itself. Causes can be strokes, tumors or traumatic brain injuries. Those affected often have normal peripheral hearing, but suffer from poor speech intelligibility and central processing disorders. Evoked potentials (AEP) and imaging procedures such as MRI help with diagnosis. Rehabilitation includes special hearing training that promotes neuronal plasticity.

Cerumen, also known as earwax, is a protective mixture of secretions from the ceruminous glands and dead skin cells in the external auditory canal. It traps dust and germs and prevents infections by containing antimicrobial substances. Normal self-cleaning occurs through jaw movements when speaking and chewing. However, excessive cerumen formation can block the ear canal and lead to hearing loss, itching or inflammation. If a plug forms, the ENT specialist gently removes the cerumen under vision.

Cerumen obturans describes a compact earwax plug that almost completely blocks the ear canal. It is caused by excessive production or incorrect cleaning, e.g. with cotton buds. Symptoms include hearing loss, a feeling of pressure and occasionally tinnitus. It is removed microscopically or by rinsing with lukewarm water. Regular check-ups and prophylactic drops prevent recurrences.

Cerumen management includes techniques for the safe removal of earwax, for example manual micro suction, irrigation or cerumen-dissolving drops. The aim is to restore the openness of the ear canal without damaging the eardrum. Professional management reduces complications such as cerumen obturans or foreign bodies in the ear. Audiological checks before and after the procedure ensure the success of the treatment. Patients receive instructions on gentle self-care.

The cochlear duct is the bony duct filled with endolymph in the cochlea in which the organ of Corti is located. It separates the scala vestibuli and scala tympani and enables frequency analysis through the basilar membrane. Vibrations of the endolymph set the membrane in motion and stimulate hair cells. Damage to the cochlear duct leads to sensorineural hearing loss and impaired tonotopy. Histological studies are investigating the regeneration potential of this structure.

The chorda tympani is a branch of the facial nerve that conveys the sense of taste from the front two-thirds of the tongue and passes through the tympanic cavity. The nerve can be irritated during otitis media or middle ear surgery, resulting in taste disturbances (dysgeusia). Symptoms usually subside after healing or removal of inflammatory stimuli. Chronic lesions require neurological clarification. The function of the chorda tympani is often tested for taste-related complaints.

Chorda myositis is an inflammation of the muscles around the chorda tympani or adjacent structures in the middle ear. It can cause pain, tinnitus and temporary hearing loss. The causes are usually viral infections or autoimmune reactions. It is treated with anti-inflammatory medication and physiotherapy. Otitis media and neuralgia should be ruled out in the differential diagnosis.

Chronic otitis is a long-lasting inflammation of the middle ear, often with perforation of the eardrum and recurrent effusions. Symptoms include chronic discharge (otorrhea), hearing loss and occasional episodes of pain. Treatment includes surgical repair, tympanoplasty and antibiotic therapy. Long-term monitoring prevents complications such as cholesteatoma. Audiometry documents the development of hearing function.

A CIC hearing aid (Completely-in-Canal) sits completely in the ear canal and is almost invisible. It uses the natural sound funnel function of the outer ear and is comfortable to wear. Due to the small design, the range and battery size are limited, but it is ideal for mild to moderate hearing loss. Fitting requires exact ear impression and fine tuning by the acoustician. Regular cleaning is important to avoid earwax deposits.

The cochlea is the spiral-shaped inner ear organ in which sound is converted into neuronal signals. Hair cells are located on its basilar membrane, which encode different frequencies depending on where they are deflected. Sensory transduction takes place through mechano-electrical conversion in the hair cells. Damage to the cochlea is the main cause of sensorineural hearing loss. Research on cochlear regeneration aims to restore lost hair cells.

A cochlear implant is an electronic inner ear prosthesis that converts sound signals into electrical impulses and transmits them directly to the auditory nerve. It consists of an external speech processor and an implanted electrode splint. CI enables deaf or profoundly hearing impaired patients to understand speech, often after a short rehabilitation phase. Indication is made by a multidisciplinary team after audiometry and MRI. Speech training and adaptation of the processor are crucial for success.

Cochleoplasty refers to surgical procedures on the cochlea, such as the removal of cholesteatomas or implant placement. Access is usually via the round window or a cochleotomy. The aim is to maintain or restore function in middle ear and inner ear disorders. Postoperative audiometry monitors hearing gain and freedom from complications.

Cochlear dead zones are areas on the basilar membrane without functional hair cells, caused by noise, age or ototoxins. They appear as horizontal gaps in the audiogram and impair speech comprehension. Dead zones are irreversible, therapy is aimed at compensation through hearing aids or CI. Mapping strategies for CIs take dead zones into account for optimal stimulation.

The cochlear nucleus in the brain stem is the first central station of the auditory pathway where auditory nerve fibers end. It is divided into ventral and dorsal parts with different tasks in time and frequency analysis. From here, signal pathways run to higher auditory centers and to the cerebellum. Lesions lead to central auditory processing deficits. Electrodenstimulation in the nucleus is used for brainstem implants.

The biological cochlear amplifier is created by the activity of the outer hair cells, which generate mechanical feedback and thus increase the sensitivity and frequency selectivity of the cochlea. This active process amplifies soft sounds by up to 50 dB and sharpens the sound resolution. Damage to outer hair cells leads to broadband hearing loss and reduced speech audiometry performance. Otoacoustic emissions indirectly measure the function of this amplifier.

A cochleotomy is the surgical opening of the cochlea, usually to fix CI electrodes in the inner cavity. Access is made carefully at the round window in order to preserve residual hearing. Precise surgery minimizes trauma and preservation of structures for possible residual function. Postoperatively, the electrode is checked by X-ray and audiometry. Complications such as perilymph leakage require immediate revision.

The inferior commissure is a nerve pathway that connects the left and right inferior colliculi in the midbrain and thus supports binaural processing of sound information. It enables the integration of time and level differences of both ears for directional hearing. Lesions lead to impaired localization and reduced speech comprehension in complex acoustic situations. Animal studies are investigating its role in auditory plasticity.

Compliance of the middle ear describes the mobility of the eardrum and ossicular chain in response to changes in pressure. It is measured using tympanometry and expressed in ml or mmho. Low compliance indicates stiffening (e.g. otosclerosis), high compliance indicates perforation of the eardrum. The compliance curve helps to differentiate between middle ear diseases. Treatment decisions for tympanoplasty or stapes surgery are based on compliance data.

The connective tissue layer of the eardrum lies between the skin and mucous membrane layer and gives it stability and elasticity. It consists of collagen fibres that optimize vibration properties. Injuries to this layer, such as perforations, impair sound conduction and require surgical reconstruction. In tympanoplasty, this layer is replaced by grafts. Histological examinations show the ability to regenerate under certain conditions.

The organ of Corti is located on the basilar membrane and contains inner and outer hair cells that convert sound into electrical signals. Inner hair cells are primary sensory cells, while outer hair cells act as cochlear amplifiers. The mechanical movement of the tectorial membrane stimulates the hair cells, whose stereocilia generate electrochemical stimuli. Damage leads to sensorineural hearing loss and reduced frequency resolution. Research is aimed at cell regeneration using gene therapy.

The development of the organ of Corti begins embryonically and is largely completed by birth. Critical phases include differentiation of hair cells and neuronal connection to the auditory nerve. Disruptions in this phase lead to congenital hearing loss. Animal models show that growth factors could stimulate regeneration. Understanding developmental biology is key to future therapies.

The membrane of Corti separates the scala media and scala tympani within the cochlea and supports the organ of Corti. Its stiffness varies along the cochlea and enables tonotopic frequency analysis. Changes due to age or noise influence membrane mechanics and hearing thresholds. Histological staining reveals microstructures and pathologies. Repair approaches test biomaterials for membrane regeneration.

Cortical Auditory Evoked Potentials (CAEP) are slow brain responses to sound stimuli, measured in the auditory cortex. They provide information about the cortical processing of sounds and speech. CAEPs are used in pediatric audiological assessments and central hearing disorders. The latency and amplitude of the waves allow conclusions to be drawn about the speed of stimulus processing. Clinical applications include monitoring CI users.

Cortical plasticity describes the ability of the auditory cortex to adapt structurally and functionally to changing stimuli. After hearing loss or CI implantation, neuronal networks reorganize themselves in order to make optimal use of residual hearing. Training and rehabilitation promote plastic processes and improve speech comprehension. Imaging studies (fMRI) show cortical reorganization after hearing therapy. Plasticity decreases with age, but remains present throughout life.

The VIII. cranial nerve carries acoustic and vestibular information from the inner ear to the brain stem. It branches into cochlear and vestibular parts and is essential for hearing and balance. Lesions lead to unilateral hearing loss, tinnitus or dizziness. Diagnosis is made by ABR and caloric testing. In the case of tumors such as acoustic neuroma, early surgical removal is indicated.

CMD refers to functional disorders of the temporomandibular joint, which can lead to ear pain, tinnitus and hearing loss through muscle tension. Misalignments change cranial mechanics and transfer tension to the meatus. Treatment includes physiotherapy, splint therapy and myoelectric stimulation. Interdisciplinary cooperation between dentistry, ENT and physiotherapy is essential. Improvement is often seen within a few weeks.

Cross-hearing occurs when a sound stimulus is perceived by the non-tested ear during an audiometric test. This distorts measurement results and makes it difficult to attribute hearing losses. Masking with white noise in the opposite ear prevents cross-hearing. Correct masking is standard in the differential diagnosis of conductive and sensorineural hearing loss. Modern audiometers support automatic masking.

The cupula is a gelatinous cap in the ampulla of each semicircular canal in which hair cells are embedded. Movements of the endolymph bend the cupula and thus mechanically stimulate the hair cells. This principle enables the detection of rotational accelerations. Dysfunctions of the cupula due to otolith detachment lead to positional vertigo. Therapy is carried out with repositioning maneuvers such as Epley.