The 10 parts of the ear and the process of receiving sound

The auditory system is relatively simple compared to those of the other senses; This is because the process by which sound vibrations turn into nerve impulses it has a linear character. 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 make up each of these sections. To complete this description we will explain the process by which the vibrations of the air become perceptible sounds for humans.

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Parts of the outer ear: from the ear to the eardrum

The outer ear It is made up of the ear, the ear canal and the eardrum or tympanic membrane. The function of this segment of the auditory system is to capture sound vibrations and channel them to 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 pinna

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 “pinna”, is made up of cartilage and skin. Its function is to collect auditory energy and redirect it to the middle ear through the ear canal.

2. Ear canal

The ear canal is a cavity that connects the ear with the eardrum. Sound vibrations reach the middle ear through this channel, which is approximately 2.5 to 3 centimeters long and barely 7 square millimeters in diameter.

3. Eardrum or tympanic membrane

The eardrum is a membrane that separates the outer ear and middle ear; strictly speaking, it is not part of any of these segments, but rather the structure used to delimit them. It is also known as the "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 the impulse transduction will take place nervous

1. Hammer, anvil and stirrup

The chain of ossicles is made up of the hammer, anvil and stapes. Amphibians, reptiles, and birds have only one bone, the columella, which is morphologically equivalent to the stirrup of mammals.

The hammer is attached to the eardrum, while the stapes connects to the cochlea; the transmission of vibrations through the ossicles causes the lymphatic fluid in the inner ear to move, a necessary step for sound transduction.

2. Oval window

The oval window is the membrane that lines the cochlea, so it is technically between the inner and middle ears. 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. It is here that the transduction of sound vibrations into nerve impulses takes place, which marks the beginning of the brain's processing of hearing.

The key structure of the inner ear is the cochlea or snail, a set of channels that rotate on themselves and that amplify the auditory signals they receive. Inside the cochlea is the organ of Corti, which is primarily responsible for hearing.

1. Semicircular channels

The semicircular canals or ducts are an organ of the inner ear composed of two compartments, the saccule and the utricle, which allow a sense of balance in association with the ossicle chain.

2. Vestibular or superior scale

The oval window of the cochlea, located on the buccal scale, connects the stapes with the rest of the inner ear. This structure is full of perilymph, a substance similar to cerebrospinal fluid that receives the vibrations of the ossicle chain.

3. Tympanic scale or inferior

Sound waves received by the upper scale are transmitted to the lower one through the perilymph since the two structures are connected by this liquid, while the basilar membrane the To stop.

4. Cochlear or mean scale

The cochlear scale is isolated from the vestibular and tympanic scale by Reissner's membrane and the basilar membrane, respectively; however, it also shares endolymph with other parts of the inner ear.

The organ of Corti is located on the middle scale, where the transduction of sound vibrations into neural impulses takes place. Hair cells found 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 nerves, 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.

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