How do we hear sounds?

This is the layout of the cochlea in its most basic form. At the base resides a group of cells called the support cells which cup, and support the signal transducers or hair cells.

Effects of damage

In this series of photographs the top image shows a cross section through a normal cochlea taken with a transmission electron microscope. The photos below are taken from the top looking down on the surface of 2 different cochlea, using a scanning electron microscope. The point of these images is to convey how sound damage affects the surface area of the support cells, which are labeled by arrows in the top photo and the boxes in the 2 bottom photos. Support cells are stressed by loud noises, which causes these cells to expand their surfaces. At some point the hair cells are forced out of position which causes them to die. In mammals, including humans, this results in permanent hearing loss.

What does severe damage look like?

When the inner ear is traumatized by specific drugs or loud noises some of the hair cells and support cells within the cochlea can be damaged or killed. When the damage is severe enough these cells are ejected from the cochlea. In humans both forms of damage are permanent and are leading causes of deafness. How can you avoid damaging your ears? Always wear ear plugs or safety earmuffs in any situation where you are exposed to loud noises. This includes rock concerts, machine shops, shooting ranges, etc. Keep the music low on your stereo headphones. As for preventing hearing loss due to antibiotic drugs always read the labels on any drugs you take. Ask your doctor if there are any side affects or substitutes. The drugs that most often cause hearing loss are those in the Aminoglycoside family, which are normally prescribed as a last resort to fight serious, life threatening infections.

Damage releases signals

Whenever cells are stressed or killed, they or their neighboring cells release chemical signals that get relayed throughout the cochlea. This communication network can tell a group of cells to die, survive, attack, run away, or in the case of the support cells within the bird cochlea, to reproduce. Scientists involved in hearing research often study birds, fish or amphibians because these organisms are able to re-grow, or regenerate ear tissues after damage. Mammals and humans are not capable of repairing the cells in the inner ear. It is hoped that our laboratory experiments will one day determine which chemical reactions control this re-growth so that this knowledge can be applied to help the hard of hearing and deaf communities.

Ability to reproduce
Nerves Reconnect
Primary teaching affiliate
of BU School of Medicine