Middle ear: tympanic membrane, ossicles, tympanum and eustachian tube. Tympanic membrane: It gradually tapers to the inner ear and is gray and translucent, which is an important sign to distinguish the outer ear from the middle ear. It is divided into three layers: the outer layer is the skin layer, which is tapered towards the inner ear, and the middle layer is composed of shallow radial fibers and deep annular fibers. The inner layer is composed of mucous membrane, which covers the cavity, so the eardrum can withstand water pressure, air pressure, anti-infection and so on. Auditory bone: the malleus, incus and stapes are collectively called the ossicular chain. Middle ear muscles: tensor tympani and stapes. It is the smallest muscle in the human body. The tensor tympani muscle is connected with the malleus, and the malleus is connected with the drum wall. The other ends of the two muscles are attached to the mucosa of the middle ear cavity. The functions of these small muscles are as follows: a. The middle ear muscle is an important part of the suspension system of the ossicular chain, so keeping the ossicular chain in a certain tension is conducive to sound transmission. B. Middle ear muscles can also play a protective role. The contraction of the middle ear muscles reduces the sound pressure transmission through the ossicular chain, thus reducing people's exposure to loud sounds. Eustachian tube: it is the only way for middle ear ventilation and drainage, and it is also the main way for middle ear infection. The nasal cavity passes through the opening of the eustachian tube. Air can enter the middle ear cavity from the outside. Open when coughing or swallowing. The balance between the internal pressure of the tympanic cavity and the external atmospheric pressure can be adjusted. Children's eustachian tube is relatively short, and the openings at both ends are almost equal in height, which is easy for bacteria to enter the middle ear cavity through the nasopharynx and cause otitis media.
Middle ear function: 1. It is a transducer, which converts the acoustic energy from the eardrum into mechanical energy and sends it to the oval window. 2. It is a supercharger. Because the areas of the eardrum (60mm2) and oval window (3 mm2) are different, it is helpful to increase the air pressure in the external auditory canal, and then the inner ear fluid with higher density is driven by the lever principle of ossicular chain, so that the pressure is increased by about 30dB.
Inner ear: It is the most complicated part of the ear. It is located behind the middle ear. This is a cavity composed of rocky bones. The cavity is filled with liquid, and the rock-like bones play a protective role. The inner ear is very important because it converts vibrating sound waves into nerve impulses. Anatomically, the inner ear consists of vestibule, semicircular canal and cochlea. There are two windows on its outer wall: an oval window and a round window. The semicircular canal maintains the balance of human body, which involves the understanding of sound. The sense of balance, dizziness and vomiting that accompany hearing problems are all related to it.