Hearing Lose Loud sounds can impair hearing for a short time. Researchers at Linköping University, Sweden, have discover a mechanism that explains how this happens. Their results are presented in the journal Proceedings of the National Academy of Sciences, PNAS. Most people have experienced hearing impairment and ear numbness after loud sounds.
After a while, hearing returns to normal. They have discover that a tiny structure in the cochlea know as the tectorial membrane plays an important role in this process; so by acting as a storage depot for calcium ions. These calcium ions contribute to regulating the function of the sensory cells,” says Anders Fridberger at the Department of Clinical and Experimental Medicine, who led the study.
Impulses of inner ear
Calcium ions, which are calcium atoms with a positive charge; so play a key role in the processes that make hearing possible. The conversion of sound waves to nerve impulses takes place in the inner ear, also known as the cochlea; which looks like a spiral snail shell. The cochlea contains many sensory cells that detect sounds and generate signals; so that are pass on to the brain.
Previous research has shown that the fluid surrounding the sensory cells; so in the cochlea has a low concentration of calcium ions. There were, however, questions surrounding this; so because sensory cells that are place in fluids with the natural level of calcium no longer work normally. The scientists at LiU have investigate the calcium ion concentration in the inner ear of guinea pigs; which is very similar to the human ear.
By fluorescently labeling the calcium ions, the researchers discover that a membrane that lies on top of the sensory cells; so the tectorial membrane, has a much higher concentration of calcium ions than the surrounding fluid. The membrane seems to function as a store; such that the sensory cells are surround by higher levels of calcium ions than previously believed.
Sensory cells cease to function
When the scientists add a substance that mops up calcium ions, the sensory cells cease to function. In the next step, they expose the inner ear to noise levels that correspond to those experience at rock concerts, which had the same effect. When we expose isolate inner ears to loud noise in the lab, the level of calcium in the tectorial membrane falls, and the sensory cells cease to function.
After a while, however, the calcium ion concentration returns to its previous level, and the sensory cells start to function again,” says Anders Fridberger. Until now, scientists have thought that the tiny membrane had a mainly mechanical function, but the discovery made by the LiU researchers suggests that the tectorial membrane may play an important role in regulating hearing by storing calcium.
We knew that the tectorial membrane is necessary for hearing, and that it must be intact and correctly locate; but it has been unclear why damage to this membrane contributes to impair hearing, says Pierre Hakizimana, one of the researchers behind the study. The research group is now planning to investigate whether the same mechanism is important in age-relate hearing impairment.