From the delicate tinkling of a needle bouncing on a glass table to the deafening roar of a plane taking off, our ears enable us to distinguish almost 400,000 sounds. The organ responsible for hearing is not the visible external ear, but a group of Small, fragile internal structures housed in a bony cavity inside the head.
Our auditory system has three parts. The outer ear is essentially composed of the auricle, which captures sound vibration and directs it to the auditory canal. The middle ear, bounded by a fine membrane (the tympanum) contains a group of three tiny bones only a few millimeters long: the hammer, the anvil and the stirrup. This chamber is connected to the nose and throat by a narrow passage, the Eustachian tube. Finally, the inner ear contains the cochlea, a liquid-filled spiral, and the cochlear nerve.
Auditory messages, relayed by the auditory nerve, end up in a zone of the cerebral cortex, the auditory cortex, which has two areas. Specific sounds are identified in the primary auditory cortex, while the secondary auditory cortex, which surrounds it, provides a more diffuse representation of sounds perceived. The areas are beside Wernicke’s area, which is involved in language comprehension.
Our auditory system functions like a complex trap that routes sound vibrations through several successive elements: air in the outer ear, a solid in the middle ear, and liquid in the inner ear. Only at the end of this series of transmissions does the real receptor, the organ of Corti, detect the frequency and intensity of sounds.
Sound, directed from the auricle through the external auditory canal, makes the tympanum vibrate. The ossicles located behind this membrane amplify the vibration and transmit it to the entrance to the inner ear, the oval window. The sound vibration then travels through the vestibular canal of the cochlea and stimulates the organ of Corti. High-frequency sounds are felt at the base of the spiral and low-frequency sounds at the apex. When the vibrations arrive at the helicotrema, they travel up the tympanic canal and leave the cochlea via the round window.