|1) Sound waves are collected by the outer ear.||2) Little bones (ossicles) focus the sound vibrations onto the cochlea of the middle ear.|
|3) The basilar membrane inside the cochlea breaks the sound waves up into different frequencies.||4) Tiny hair cells which live on the basilar membrane translate mechanical vibrations into patterns of nerve impulses.|
Incoming sounds are decomposed into their frequency components at the basilar membrane. The near ("basal") end of the basilar membrane resonates to high frequencies, and the far ("apical") end resonates to low frequencies. Vibrations at different locations on the basilar membrane therefore reveal what frequencies are present in the sound. This little video shows you how the vibrations might look if the basilar membrane could be "rolled out in front of you".
The vibration patterns of the cochlea may remind you of the spectrogram
which you may have played with earlier in this guide.
Your basilar membrane is lined with tiny hair cells, which are responsible for converting mechanical vibration of the basilar membrane to a chemical signal that stimulates your auditory nerve.
Hair cells in your ear come in two flavours: one row of inner hair cells and three rows of outer hair cells. The inner hair cells are heavily connected to the auditory nerve, and they send sound information to your brain. The job of the outer hair cells, in contrast, is to amplify the sound vibrations by dancing along. Literally! (See for yourself in this little video here.)
Hair cells are easily damaged, for example, by listening to extremely loud music. As you grow older, hair cells at the high frequency end of the cochlea also tend to wear out.
The pictures below show electron micrographs of healthy hair cells (left) and hair cells after exposure to excessive noise (right).
In mammals, dead hair cells do not grow back. Damage to hair cells is a leading cause of hearing loss. Take care of your hair cells!
As we age, our auditory sensitivity often declines, and the average decline is perhaps a lot more than you might think! Use the buttons below to start or stop a little stand-up comedy video clip, and to select to hear it the way it would sound to an average elderly person some 60, 70, or 80 years old, or someone completely deaf. You can also add "multi-speaker babble" background noise. Hearing the comedian is, unsurprisingly, more difficult in the presence of background noise, but it is even harder with background noise and old age hearing noise.
If you are fairly young and your hearing is good, you may be surprised, even appaled, at how much worse the simulated "elderly hearing" is. Is it really that bad? The answer to that is: it depends.