HOW WE HEAR – ANATOMY AND FUNCTION OF THE EAR
Our hearing is an amazing, very complex sensory organ that not only allows us to pick up and recognize sounds and noises, but also to maintain balance and much more. But how does hearing work exactly?
The process of hearing begins in the outer ear: Here, the auricle picks up sound waves and transmits these impulses to the eardrum (lat. membrana tympani). The eardrum begins to vibrate and transmits the vibrations to the three ossicles of the middle ear – malleus, incus and stapes. These amplify the vibrations and transmit them to the cortical organ (lat. cochlea).
The cochlea, which is only a few millimeters in size and is also known as the “cochlea” due to its multiple curved shape, consists of three chambers filled with fluid (endolymph): the scala vestibuli, the scala media and the scala tympani, which are separated from each other by membranes. On the scala media is the organ of Corti with thousands of sensory hair cells that form the actual sensors of hearing: Arranged in rows, they perform different tasks depending on their location: The inner hair cells send information to our brain and thus form our hearing, the outer hair cells amplify or attenuate this information.
Vibrations in the cochlea
When a mechanical sound wave hits the cochlea, the fluid in the chambers (scalen) and the membranes start to vibrate. The hair cells are excited by the sound-induced fluid shift in the scala media, generating electrical charges. Thousands of nerve cells of the auditory nerve (lat. nervus cochlearis) register these charges and in turn transmit them to the brain via the auditory nerve. Here, the auditory cortex processes them into acoustic information: They are transformed into the diverse world of sounds and noises and assigned accordingly or interpreted as speech.
In addition to hearing, our ears are also responsible for our balance and spatial orientation: The balance organs in the inner ear register our body posture and movements and also send this information to the brain, where it is processed.