The human ear has a very complex anatomical structure that allows you to capture sound waves, determine the direction of the sound source and correctly identify it. It consists of three main sections: the outer, middle and inner ear. Each of which has strictly defined functions and special structure. The human middle ear primarily converts sound waves into nerve impulses. This is its main, but not the only function.
General structure and principle of operation
The middle ear begins just behind the eardrum, which is located at the end of the ear canal and separates it from the outer ear. There are three main elements in the middle ear:
- tympanic cavity;
- mastoid processes;
- auditory tube.
The eardrum is a small piece of thin connective tissue that is directly involved in the transformation of sound waves captured by the outer ear.
The tympanic cavity of the middle ear is located in the notch of the temporal bone. Inside it, in the immediate vicinity, are the three smallest bones of the human skeleton: the hammer, the stapes and the incus. Acoustic waves cause the eardrum to vibrate, and these vibrations are transmitted to the bones. And the stapes through the oval window sends a signal to the liquid that fills the inner ear - perilymph.
Interestingly, the design of the ossicles allows not only transmitting, but also significantly amplifying sound. The surface of the stapes is an order of magnitude smaller than the area of the tympanic membrane, which means that it hits the oval window much harder, giving a person the opportunity to hear even very quiet sounds.
Protective functions of the middle ear
The function of the middle ear is not limited to sound conduction. It is also a reliable protective barrier that protects the delicate inner ear from:
- ingress of moisture, particles of dust and dirt;
- penetration and reproduction of pathogenic microorganisms;
- too intense exposure to a sound wave;
- sudden changes in atmospheric pressure;
- mechanical stress.
The middle ear cavity is filled with air and is connected to the nasopharynx via the Eustachian tube. Under normal conditions, the air pressure is the same on both sides of the tympanic membrane. But if the atmospheric pressure changes sharply in any direction, then this stretches the eardrum and can lead to its rupture.
This phenomenon is called barotrauma. The same thing occurs when a sharp dive to great depths. To prevent barotrauma, diving should be done slowly. And when the plane is taking off or landing - open your mouth or make swallowing movements often.
The anatomy of the middle ear can partially compensate for loud sounds. It houses two very small muscles, one of which controls the tension of the tympanic membrane, and the other controls the amplitude of the stapes. The natural defense mechanism provides a reflexive contraction of these muscles when sounds are too loud. The movement of the stapes is limited and the ear's sensitivity is temporarily reduced. It takes about 10 ms to trigger it. Therefore, during explosions, shots and other impetuous sounds, it does not have time to compensate for the noise.
Diseases of the middle ear
The structure of the middle ear is such that in case of its diseases, the normal conductivity of sound suffers first of all and the threshold of auditory sensitivity is sharply reduced. The causes of inner ear disease are most often trauma, hypothermia, or exposure to pathogenic microorganisms.
Moreover, viruses and bacteria can enter the ear not only through the external auditory canal, but also from the mouth or nose through the Eustachian tube. That is why ARVI, flu, rubella, tonsillitis are often complicated by otitis media.
Among the most common diseases of the middle ear, doctors note:
- acute and chronic otitis media;
- barotrauma;
- mechanical injury;
- congenital pathologies;
- hearing loss of 1-4 degrees.
Purulent otitis media is especially dangerous, which, in the absence of proper treatment, can lead to inflammation of the meninges (meningitis) and even general blood poisoning (sepsis). Pus collects behind the eardrum and presses on it, causing severe pain. Sometimes it is partially perforated, and in some cases, it is completely ruptured, which can lead to partial or complete hearing loss.
Unfortunately, the structure of the middle ear is such that diseases appear already at the stage when the inflammatory process has developed. The main symptoms of the disease of this organ are: a sharp shooting pain, an increase in body temperature, often reddening of the tragus, headache, periodic dizziness.
With otitis media, pus or a yellowish exudate with an unpleasant odor may be discharged from the ear. If these symptoms appear, you should immediately consult a doctor. Delay and improper treatment can lead to very serious consequences.
