As the name suggests, the ear canal is a passage in the ear that plays a crucial role in hearing. A distinction is made between the inner ear canal and the outer ear canal.
What is the ear canal?
Schematic diagram showing the anatomy of hearing and the auditory canal. Click to enlarge. The auditory canal is a passage relevant to the sense of hearing. In the human ear there are two types of such passages, one is responsible for the passage of relevant nerves and blood vessels towards the brain, and the much better known one describes the entrance to the ear. For hearing, both auditory canals are of enormous importance. What happens once they are blocked is shown to us by the symptoms of earwax plug and acoustic neuroma, respectively.
Anatomy and structure
The term ear canal can refer to two different passages that run within the human ear. A distinction is made between the “internal auditory canal“(meacus acustis internis) and the “external auditory canal”(meacus acustis externis). According to its designation, the auditory canal can be assigned to the inner ear or the outer ear. The external auditory canal, belonging to the outer ear, connects the pinna with the eardrum. It measures about 3.5cm in length, has a diameter of 5mm and is the direct entrance to the ear visible from the outside. It is formed by cartilage on the outside and bone on the inside. The internal auditory canal, on the other hand, runs completely inside a part of the skull called the petrous bone and opens into the posterior fossa.
Function and tasks
While the internal auditory canal provides the passage for important facial and auditory nerves (faciliar nerve, cochlear nerve, vestibular nerve), as well as blood vessels (labyrinthine artery) into the interior of the skull, the external auditory canal is important for the transport and amplification of sound. This amplification occurs in self-resonance and is also referred to as “open ear gain” (OEG). It is interesting to note that certain wavelengths are amplified more than others – in particular, the frequency range from 2 to 5 kilohertz experiences an amplification of up to 20 decibels. This range also includes the overtones of the human voice, which are extremely relevant for speech comprehension. Female and childlike voices in particular fall within this frequency spectrum, which is one of the reasons for preferring to use female voices for calling out passengers and similar announcements. In addition to this direct function, the external auditory canal also has important protective mechanisms, such as bristle hairs (tragi) and sebaceous glands. The bristle hairs mechanically protect the ear from the penetration of foreign bodies or insects, and the sebaceous glands transport dead skin cells, dust and dirt particles back out with the earwax (cerumen). In addition, this earwax also contains components that keep insects away and can fight or even kill bacteria or fungi, thus keeping the ear canal clear.
Diseases and ailments
Just with the earwax of the ear canal, however, some problems can occur – so it often happens that due to improper cleaning (for example, with a cotton swab) or overproduction of earwax a plug is formed, which severely restricts hearing. Fortunately, such a hearing loss is only temporary and can be cured by the attending physician by removing the so-called ceruminal plug. Another common form of the disease is the inflammation of the external auditory canal, the so-called “otitis externa” (not to be confused with the middle ear inflammation “otitis media“). This disease can also be promoted by improper removal of earwax: If the ear canal loses its protective coating, it is more susceptible to bacteria and viruses. The result is partial or complete infection of the ear canal and associated severe ear pain, itching, redness and possibly even temporary hearing loss. Fungal infections of the ear canal are particularly unpleasant, although much less common. These, once spread, are extraordinarily persistent and usually require prolonged therapy with repeated treatment. Aspergillus niger, a blackish mold, is particularly aggressive here and should be treated urgently by a physician. In the area of the inner auditory canal, mainly acoustic neuromas, benign tumors formed by Schwann’s cells, lead to disturbances of perception.These mainly affect hearing (hearing loss or ringing in the ears) and the sense of balance (vertigo). Another name for tumors of this type is vestibular schwannoma, named after the vestibular nerve, from whose Schwann’s cells it forms to eventually narrow the ear canal.
