By the tympanic cavity, physicians mean a cavity of the middle ear in which the auditory ossicles are housed. In addition to the hearing process, the tympanic cavity is involved in middle ear ventilation and pressure equalization. Tympanic effusion is the most well-known complaint associated with the tympanic cavity.
What is the tympanic cavity?
The tympanic cavity is a part of the middle ear. It is a cavity system with six different walls. This cavity system is particularly relevant for ventilation, sound amplification and pressure equalization. The tympanic cavity begins just behind the eardrum and consists of the tympanic dome, the middle tympanic cavity and the tympanic basement. The middle space forms the largest portion and is directly adjacent to the eardrum. The so-called oval window connects the tympanic cavity with the cochlea of the inner ear.The structure of the tympanic cavity also houses the auditory ossicles. The incus and malleus are located in the dome of the structure, where the malleus is attached to the tympanic membrane and is in articulated connection with the incus and stapes. With a length of about twelve to 15 millimeters, the tympanic cavity is about three to seven millimeters wide. The internal volume is about one cubic centimeter.
Anatomy and structure
The tympanic cavity has a total of six walls. From the cavity system, there are connections primarily to the nasopharynx and the inner ear through various windows and orifices. In the upper part of the tympanic cavity there is an access to the skull bone. The upper boundary of the tympanic cavity is a thin plate of bone, also called the tympanic roof. The anterior wall of the middle part of the tympanic cavity contains the internal carotid artery. The tympanic muscle also sits in this area. The tuba auditiva, which connects the tympanic cavity to the nasopharynx, also opens into the same wall. The lateral wall of the tympanic cavity forms the tympanic membrane itself. A nerve branch crosses in here, also known as the tympanic cord. The curved middle wall of the tympanic cavity demarcates the cavity structure from the inner ear. The posterior wall forms the boundary with the mastoid process of the cranial cavities. Four arteries supply the tympanic cavity and open into lymph and nerve structures. To a large extent, the tympanic cavity is lined by a thin mucosa. This mucosa consists of an isoprismatic epithelium with mucus-producing goblet cells. In the region of the ossicles, this layer transitions into a thick squamous epithelium.
Function and tasks
Because the tympanic cavity is a cavity system, this anatomical structure is permanently filled with air. Thus, ventilation of the entire middle ear occurs through the air-filled cavity system. In addition, the tympanic cavity serves to functionally house the ossicles of the malleus, incus and stapes. These bones are interconnected and together amplify all acoustic signals. This is what makes the impression of hearing as humans know it possible in the first place. The membrane of the tympanic cavity is able to vibrate for the sake of the bones. When the eardrum vibrates, for example, due to sound, this is transmitted to the attached malleus. The hammer passes the vibrations on to the incus and the stapes. From these two ossicles, the sound is transmitted to the inner ear. This transmission takes place through the oval window in the tympanic cavity. Thus, the tympanic cavity is significantly involved in the hearing process. The cavity system is also an instance of pressure equalization through the confluent tuba auditiva, which occurs primarily through the nasopharynx. Pressure equalization is especially relevant in situations under water or at high altitudes. This is because when large differences in altitude or pressure are overcome in a very short time, there is a pressure gradient between the external auditory canal and the tympanic cavity. The eardrum is then pressed into the cavity system. Pressure equalization via the auditory tuba ensures the integrity of the eardrum in such situations, but fluid is also drained from the middle ear through the auditory tuba.
Diseases
The so-called tympanic effusion is one of the most common diseases of the tympanic cavity. Most often, this phenomenon is the result of a cold illness with respiratory infection, but allergies can also trigger a tympanic effusion. As a rule, a purulent middle ear infection occurs in the context of a tympanic effusion. The tuba auditiva swells and hardly allows air to enter the tympanic cavity.Ventilation of the middle ear is thus no longer possible. High pressure builds up in the tympanic cavity and fluid accumulates. As a result, the eardrum bulges inward. In most cases, hearing loss also develops. Tympanic cavity effusions can lead to a chronic middle ear infection. After an otoscopy, the doctor usually treats a tympanic effusion with medication. A rarer but all the more consequential disease of the middle ear is chronic bone suppuration. In this disease, the middle ear is permanently under pressure due to an air supply disorder. The eardrum retracts into the middle ear space and the chain of ossicles in the tympanic cavity is damaged. The skin of the external auditory canal comes into contact with the middle ear mucosa and the ossicles slowly degrade as part of an aggressive inflammation. The ossicles of the tympanic cavity can also degrade due to a condition called otosclerosis, which promotes deafness. Sometimes, however, paralysis of the facial nerve makes itself felt as a middle ear complaint, since the facial nerve enters the tympanic cavity there.
