The 10 parts of the ear and the sound reception process
The auditory system is relatively simple compared to those corresponding to other senses; This is because the process by which the sound vibrations become nerve impulses It has a linear character. The sound is transmitted from the ear to the auditory nerve, and from it to the brain, by a chain of internal structures.
In this article we will describe the outer, middle and inner ear , the main components of the auditory system , as well as the substructures that form each of these sections. To complete this description we will explain the process by which the vibrations of the air become sounds perceptible to humans.
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Parts of the outer ear: from the ear to the eardrum
The outer ear is composed of the ear, the ear canal and the eardrum or tympanic membrane. The function of this segment of the auditory system is to capture the sound vibrations and channel them towards the innermost parts of the ear. In this process some of the frequencies collected are increased and others reduced, so that the sound is modified.
1. Ear or ear pin
The ear is the outermost component of the auditory system, and the only one that can be seen from the outside. This structure, also known as the "auricular pavilion", is composed of cartilage and skin. Its function is to collect the auditory energy and redirect it to the middle ear through the ear canal.
2. Auditory channel
The auditory canal is a cavity that connects the ear to the eardrum. The sound vibrations reach the middle ear through this channel, which is approximately 2.5 to 3 centimeters long and only 7 square millimeters in diameter.
3. Tympanic membrane or tympanic membrane
The eardrum is a membrane that separates the outer ear and the middle ear ; Strictly speaking, it is not part of any of these segments, but rather it is the structure that is used to delimit them. It is also known as "tympanic membrane".
Middle ear: the chain of ossicles
After reaching the eardrum, the sound vibrations are transmitted through the ossicles of the middle ear to the oval window of the cochlea, where transduction will be carried out in nerve impulses.
1. Hammer, anvil and stirrup
The chain of ossicles is formed by the hammer, the anvil and the stirrup . Amphibians, reptiles and birds have only one bone, the columella, which is morphologically equivalent to the stapes of mammals.
The hammer is attached to the eardrum, while the abutment connects to the cochlea; the transmission of vibrations by the ossicles causes the lymphatic fluid of the inner ear to move, a necessary step for the transduction of sound.
2. Oval window
The oval window is the membrane that covers the cochlea, so it is technically located between the inner ear and the middle. The vibrations in the eardrum are transmitted through the ossicles to the oval window, which consequently also vibrates, stimulating the inner ear.
Inner ear: the cochlea and transduction
The inner ear is a cavity that is located inside the skull. This is where the transduction of sound vibrations in nerve impulses is carried out, which marks the beginning of the auditory brain processing.
The key structure of the inner ear is the cochlea or cochlea , a set of channels that rotate on themselves and that amplify the auditory signals they receive. Within the cochlea is the organ of Corti, responsible for the hearing.
1. Semicircular canals
The semicircular canals or ducts are an organ of the inner ear composed of two compartments, the saccule and the utricle, which allow the sense of balance in association with the ossicular chain.
2. Vestibular or superior scale
The oval window of the cochlea, which is located in the vestibular scale, connects the abutment with the rest of the inner ear. This structure it is full of perilinfa , a substance similar to the cerebrospinal fluid that receives the vibrations of the ossicular chain.
3. Tympanic scale or lower
The sound waves received by the upper scale are transmitted to the lower one through the perilymph since the two structures are connected by this fluid, while the basilar membrane separates them.
4. Cochlear or average scale
The cochlear scale is isolated from the vestibular and tympanic scars by Reissner's membrane and basilar membrane, respectively; however, it also shares endolymph with other parts of the inner ear.
The organ of Corti is located on the medium scale , where the transduction of sound vibrations in neural impulses is carried out. The hair cells that are in this structure allow transduction.
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5. Auditory or vestibulocochlear nerve
The vestibulocochlear or auditory nerve, composed in turn by the cochlear and vestibular nerve, transmits information about sound and balance from the inner ear to the central nervous system . The vestibulocochlear nerves constitute the eighth of the twelve cranial nerves.
- Related article: "Cranial pairs: the 12 nerves that leave the brain"
