The caloric test checks the function of the horizontal semicircular canals by stimulating the ear canal with warm or cold water or air. The temperature difference causes convection of the endolymph, which triggers nystagmus (uncontrollable eye movements) and thus reveals the vestibular function. The strength and direction of the nystagmus provide information about the integrity of the vestibular system and its central connections. This procedure is particularly important for diagnosing unilateral vestibular deficits and clarifying symptoms of vertigo. Side effects are rare, but may temporarily increase nausea or dizziness.

The semicircular canal is a bony canal in the inner ear filled with endolymph that registers rotational movements of the head. Each of the three orthogonally arranged canals (horizontal, superior, posterior) contains a sensory capsule (ampulla) with hair cells that are mechanically stimulated when fluid flows. 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, such as those that occur in benign paroxysmal positional vertigo, lead to severe episodes of dizziness. Caloric testing and video nystagmography are standard methods for testing their function.

The transverse capitis muscle, also part of the deep neck muscles, 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 located in the postauricular region is sometimes associated with ear pain and tinnitus. Manual therapy and physiotherapeutic stretching exercises relieve muscular imbalances and alleviate accompanying symptoms. During the clinical examination, the therapist pays attention to pain radiating toward the ear.

A cartilaginous earpiece is a custom-made otoplasty made of flexible material that is inserted into the ear canal and seals the hearing aid components tightly. It transmits sound optimally to the internal device and prevents feedback. Its soft texture allows it to adapt to the shape of the ear and offers comfort for long periods of wear. Hygienic cleaning and regular replacement are important to prevent wax buildup and skin irritation. Custom-made earpieces 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 include stroke, tumors, or traumatic brain injuries. Those affected often have normal peripheral hearing, but suffer from poor speech comprehension and central processing disorders. Evoked potentials (AEP) and imaging techniques such as MRI help with diagnosis. Rehabilitation includes special hearing training that promotes neural plasticity.

Cerumen, also known as earwax, is a protective mixture of secretions from the cerumen 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 doctor gently removes the cerumen under visual control.

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 swabs. Symptoms include hearing loss, a feeling of pressure, and occasionally tinnitus. Removal is performed microscopically or by rinsing with lukewarm water. Regular check-ups and prophylactic drops prevent recurrence.

Cerumen management includes techniques for the safe removal of earwax, such as 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 passageway in the cochlea filled with endolymph, which contains the organ of Corti. 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 impairs tonotopy. Histological studies are investigating the regeneration potential of this structure.

The chorda tympani is a branch of the facial nerve that transmits taste sensations from the front two-thirds of the tongue and passes through the tympanic cavity. During otitis media or middle ear surgery, the nerve can become irritated, leading to taste disorders (dysgeusia). Symptoms usually subside after healing or removal of inflammatory stimuli. Chronic lesions require neurological evaluation. The function of the chorda tympani is often tested in cases of taste-related complaints.

Chorda myositis refers to 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. Treatment involves anti-inflammatory medication and physical therapy. Otitis media and neuralgia must 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 recurring effusions. Symptoms include chronic discharge (otorrhoea), 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 (Completely-in-Canal) hearing aid sits completely inside the ear canal and is virtually invisible. It uses the natural sound funnel function of the outer ear and is very comfortable to wear. Due to its small size, its range and battery size are limited, but it is ideal for mild to moderate hearing loss. Fitting requires an exact ear impression and fine tuning by the audiologist. Regular cleaning is important to prevent wax buildup.

The cochlea (snail) is the spiral-shaped inner ear organ in which sound is converted into neural signals. Hair cells are located on its basilar membrane, which encode different frequencies depending on the location of deflection. Sensory transduction occurs through mechano-electrical conversion in the hair cells. Damage to the cochlea is the main cause of sensorineural hearing loss. Research into 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 array. CI enables deaf or severely hard-of-hearing patients to understand speech, often after only a short rehabilitation phase. A multidisciplinary team determines the indication after audiometry and MRI. Speech training and adjustment of the processor are crucial for success.

Cochleoplasty refers to surgical procedures on the cochlea, such as the removal of cholesteatomas or the placement of implants. Access is usually gained via the round window or a cochleotomy. The aim is to preserve or restore function in cases of middle ear and inner ear disorders. Postoperative audiometry checks hearing gain and ensures that there are no 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 aims to compensate for them with hearing aids or CI. Mapping strategies for CI take dead zones into account for optimal stimulation.

The cochlear nucleus in the brainstem is the first central station of the auditory pathway, where auditory nerve fibers terminate. It is divided into ventral and dorsal parts with different tasks in time and frequency analysis. From here, signal pathways lead to higher auditory centers and the cerebellum. Lesions lead to central auditory processing deficits. Electrode stimulation in the nucleus is used in 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 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 carefully gained at the round window in order to preserve residual hearing. Precise surgery minimizes trauma and preserves 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, thereby supporting binaural processing of sound information. It enables the integration of time and level differences between both ears for directional hearing. Lesions lead to disturbances in localization and reduced speech comprehension in complex acoustic situations. Animal studies are investigating its role in auditory plasticity.

Middle ear compliance describes the mobility of the eardrum and ossicular chain in response to pressure changes. It is measured using tympanometry and expressed in ml or mmho. Low compliance indicates stiffness (e.g., otosclerosis), while high compliance indicates eardrum perforation. The compliance curve helps to differentiate between middle ear disorders. 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 layers and gives it stability and elasticity. It consists of collagen fibers that optimize vibration properties. Injuries to this layer, such as perforations, impair sound conduction and require surgical reconstruction. In tympanoplasty, this layer is replaced with grafts. Histological examinations show that regeneration is possible under certain conditions.

The organ of Corti sits 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 focused on cell regeneration using gene therapy.

The development of the organ of Corti begins in the embryo and is largely complete by birth. Critical phases include the differentiation of hair cells and neural connections to the auditory nerve. Disruptions during 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 Corti membrane 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 affect 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 cortical processing of sounds and speech. CAEP are used in pediatric audiological assessments and central hearing disorders. The latency and amplitude of the waves allow conclusions to be drawn about stimulus processing speed. 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, neural networks reorganize themselves to make optimal use of residual hearing. Training and rehabilitation promote plastic processes and improve speech comprehension. Imaging studies (fMRI) show cortical restructuring after hearing therapy. Plasticity decreases with age but remains present throughout life.

The VIII cranial nerve transmits acoustic and vestibular information from the inner ear to the brainstem. It branches into cochlear and vestibular parts and is essential for hearing and balance. Lesions lead to unilateral hearing loss, tinnitus, or vertigo. Diagnosis is made using ABR and caloric testing. Early surgical removal is indicated for tumors such as acoustic neuroma.

CMD refers to functional disorders of the temporomandibular joint that can lead to ear pain, tinnitus, and hearing loss due to muscle tension. Malocclusions alter the mechanics of the skull and transfer tension to the meatus. Treatment includes physical therapy, splint therapy, and myoelectric stimulation. Interdisciplinary collaboration between dentistry, ENT, and physical therapy is essential. Improvement is often seen within a few weeks.

Cross-hearing occurs when a sound stimulus during an audiometric test is perceived by the ear that is not being tested. This distorts the measurement results and makes it difficult to classify hearing loss. Masking with white noise in the opposite ear prevents cross-hearing. Correct masking is standard practice 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, thereby mechanically stimulating the hair cells. This principle enables the detection of rotational accelerations. Dysfunctions of the cupula due to otolith detachment lead to positional vertigo. Treatment involves repositioning maneuvers such as Epley.