The structure of the ear is as follows!
time2024/01/19
- Deep within the external auditory canal lies an eardrum, as thin as a piece of paper and translucent like a cicada's wing.
Deep within the external auditory canal lies an eardrum, as thin as a piece of paper and translucent like a cicada's wing. This delicate membrane serves as the boundary between the outer and middle ear, effectively isolating the middle ear from the external environment. As a result, the middle ear and external auditory canal are not directly connected in a healthy ear. Some individuals have a straight external auditory canal, allowing them to view the white eardrum with the aid of light. However, in most cases, specialized otological instruments are required to obtain a clear view.
The main function of the eardrum is to move inwards and outwards as the sound wave enters the ear canal, similar to the shell of a drum. Because the eardrum is very thin, too much impact air, foreign objects and infection can cause the eardrum to rupture, often called a tympanic rupture or perforation. Like a slap.A ruptured eardrum will usually heal on its own if there is no infection or pus. The healing time varies from days to months. During this time, it is important to avoid getting water into the ear canal, avoiding colds, pinching your nose and blowing air (more on this later). In addition to acute rupture, the eardrum can also develop local invagination for a variety of reasons. Most of them are the upper 1/3 of the eardrum which looks relatively loose, also known as the relaxation part, and the lower 2/3 is the tension part. This part is like the shell of the eardrum, which mainly plays the role of sound transmission. Perforation of this part will cause hearing loss. The invagination of the relaxation part will cause the shed epithelial tissue to be unable to be discharged, so it will accumulate and grow continuously, compressing inwards and destroying the surrounding bones and structures, and also causing infection. This is the formation of a cholesteatoma, which must be surgically removed as soon as possible.
It is unlikely that a perforation of the tympanic membrane lasting more than three months can be repaired and restored to normal condition and function by relying on the healing ability of the human body. At this point, an otologist is needed to help with what is called tympanic membrane repair surgery. Although it is called a tympanic membrane repair operation, it does not repair the tympanic membrane as the name suggests. In fact, the doctor's job is to enter the ear canal through an operating microscope or otoendoscope, see the structure of the eardrum, remove the scar tissue that has lost its ability to grow at the edge of the perforation with a micro instrument, expose the normal three-layer structure of the eardrum, and then use artificial materials or membrane-like tissues from elsewhere in the body, such as the fascia covering the temporal muscle, the fascia or fat tissue, or the cartilage sheet covering the tragus cartilage, form a bridge at the perforation site so that the skin and mucous epithelial tissue in the three-layer structure of the previously freshly exposed tympanic membrane will crawl along the bridge and eventually close the tympanic membrane perforation. The bridging tissue will be destroyed and reabsorbed in the later reconstruction process to become the eardrum structure or directly participate in the eardrum reconstruction. The success of eardrum repair depends on the body's ability to repair itself, the ventilation function of the middle ear and post-operative care.
Beyond the eardrum is the mysterious middle ear cavity, a complex structure that resembles the inside of a watch. But the eardrum is not an isolated layer of thin structure. To complete the transmission of sound, in addition to the bone wall (tympanic membrane) that surrounds the ear canal and the bone edge of the upper wall of the ear canal that closes the bottom of the ear canal, the upper part of the eardrum is also wrapped with a hammer bone, which is shaped like a hammer. The handle of the hammer is wrapped around the eardrum, the head of the hammer is pointing upwards and the inside is connected to the incus by ligaments, the other end of the incus is connected to the stirrup shaped like a stirrup by ligaments.
The oval bone plate closes the entrance to the inner ear with a circle of ligaments. The transmission system made up of all three ossicles, known in medicine as the ossicular chain, is located in the bony fossa in the middle and upper part of the inside of the eardrum. Otologists call this attic-like space the upper tympanic chamber, where two muscles, many ligaments and fasciae hold this precise sound transmission system in place like a rope. When the tympanic membrane receives sound and is affected by internal and external activity, it drives the internal and external movement of the malleus. The head of the malleus transmits the movement to the anvil and the anvil to the stapes. Finally, it will cause the internal and external piston movement of the stapes base plate and transmit the kinetic energy of the tympanic membrane to the inner ear.
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The ossicular chain is one of the most sensitive structural systems in the human body. Its normal functioning allows us to perceive the change in sound frequency from 20Hz to 20000hz and the change in sound loudness of 1dB. Of course, the normal functioning of the ossicular chain requires that the middle ear cavity is in a normal pressure state and that the middle ear mucosa is in a normal state. Once the middle ear pressure or middle ear mucosa changes, such as Eustachian tube dysfunction, eardrum perforation and middle ear inflammation, it will affect the activity of the ossicular chain and cause symptoms of discomfort, including ear tightness, hearing loss, tinnitus, etc. To avoid these situations, the human body has developed many protective mechanisms. For example, to prevent perforation of the fragile eardrum, the human body hides the eardrum in the deep external auditory canal, surrounded by hard bones. The external auditory canal has a special curved shape to prevent water from entering. To prevent insects and dust from entering, there are cerumen glands. To prevent sudden changes in pressure in the middle ear, the opening and closing pressure of the Eustachian tube is regulated (the Eustachian tube is, as the name suggests, a tube that connects the middle ear and the nasopharyngeal cavity).
In order to reduce the damage to the inner ear caused by the sudden amplification of external sounds, two muscles have been attached: the tensor tympani muscle, which is attached to the neck of the malleus, and the stapes muscle, which is attached to the neck of the stapes. As well as stabilising the ossicular chain, these two muscles have important protective functions. When the stapes muscle is stimulated by loud sounds (such as thunder or someone talking loudly into your ear), it can contract, pulling the stapes plate outwards, reducing the activity of the stapes and reducing the sound energy entering the inner ear. The tensor tympani muscle contracts as needed when the human body performs chewing and other actions, pulling the handle of the malleus inward, and the tympanic membrane is stretched, reducing the transmission of low-frequency sound generated by chewing and improving the transmission of high-frequency sound, so that we can still effectively perceive sound while chewing.