![]() How humans hear Step 1: Sound waves enter the ear. Our brain uses these signals to organize and communicate with the external world. “It's quite a complex and intricate system,” Omid Mehdizadeh, MD, an otolaryngologist ( ENT) at Providence Saint John’s Health Center in Santa Monica, Calif., tells Healthy Hearing.īut how exactly does this process unfold? We've put together a step-by-step explanation of how people hear-from the moment sound waves arrive to the outer ear, then travel through the middle and inner ear and transform into meaningful signals sent on to the brain. The study is a collaboration between Uppsala University, Canadian researchers at Western University and University of Saskatchewan, and the company Canadian Light Source Inc.Pause to think about it, and our body’s ability to translate noise into sound is incredible. ![]() Showing exactly what the patient's cochlea looks like enables the technology to be individualised better and each area stimulated with the right frequency. A CI is a hearing aid where one component is placed in the cochlea to provide direct electrical stimulation of the auditory nerve, while another part is attached to the outside of the skull. The researchers therefore think the new knowledge may prove immensely important for people who, owing to grave hearing impairments, have cochlear implants (CIs) inserted. ![]() Human ear canals and nerves are not entirely uniform in appearance. This information is mediated to the brain via 30,000 precisely tuned fibres in our hearing nerve," Helge Rask-Andersen explains. The hair cells are attached to a 34-millimetre-long basilar membrane, and are also tuned by 12,000 outer hair cells so that we can hear every volume level. Unlike the piano, which has 88 keys, we have about 3,400 internal auditory hair cells, all of which encode distinct frequencies. "This kind of map is comparable to a piano, with the keys being analogous to all the similarly coded frequencies. This research has made it possible to work out the locations of the various frequencies in the cochlear nerve, and enabled the creation of a three-dimensional tonotopic frequency map. Since the radiation is too strong to be used on living human beings, donated ears from deceased people were investigated instead. To do so, they used synchrotron X-rays, an advanced and powerful form of tomographic imaging. The researchers have now studied the details of this process, almost down to cell level. High-frequency sounds reach the sound-sensitive hair cells in the lower part of the cochlea, while low-frequency sounds are absorbed in the corresponding way in the upper parts of the cochlea. When the sound waves are captured by the cochlea of the inner ear, fibrous connective tissue and sensory cells separate the various frequencies. Frequency is measured in hertz (Hz), and the human ear can perceive frequencies of between 20 and 20,000 Hz. Sound waves have differing frequencies - that is, the number of vibrations they make every second varies according to whether it is a high-pitched sound, which causes more vibrations per second, or a low-pitched one, which results in fewer. ![]() "This can make treatment with cochlea implants for the hearing-impaired more effective," says Helge Rask-Andersen, Professor of Experimental Otology at Uppsala University. ![]()
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