¿Por qué nos pitan los oídos?- Ringing in your ears explanation.
Hoy un alumno ha preguntado una duda en clase de esas a las que tengo que contestar: No lo se.
Como profesor cuesta pronunciar esas tres palabras pero es realmente reconfortante decirlas con total humildad y a ser posible añadir, “no lo se, pero intentaré averiguarlo”.
He encontrado una página web que explica bastante bien la causa de ese molesto pitido en los oídos, copio directamente de allí (http://zidbits.com/2013/02/what-causes-spontaneous-ringing-in-our-ears/)
Before we can understand how and why tinnitus occurs, we need to know how we hear. More specifically, we need to know how the ear turns vibrations in the air into electrical signals, signals which our brain processes then interprets as sound. That starts with the mammalian cochlea.
The mammalian cochlea has two types of sensory hair cell; the outer and inner hair cells. These cells are what detects then converts vibrations or movement into electrical signals. When a sound enter the ear, it causes pressure fluctuations within the inner ear. The inner ear is filled with fluids, fluids which help facilitate the transfer of these vibrations. They vibrate down a thin, spiral trampoline-like structure called the basilar membrane. When this membrane moves, even slightly, it is detected by the inner hair cells. These cells are located on top of the basilar membrane. When they detect these vibrations, they relay the signals to the brain via the auditory nerve.
While sound vibrations travel efficiently through the liquid in your inner ear, it doesn’t do so without cost. If you have ever tried to run in a pool or in water, you know it’s much more difficult than running on land thanks to the viscosity and friction of water. This is where the outer hair cells shine. Like inner hair cells, they also detect movement on the basilar membrane. However unlike the inner hair cells, they are capable of producing vibrations themselves. Instead of sending a bunch of signals to the brain, possibly over stimulating it, their job is to expand and contract in time with the vibrations they detect. This cancels out the friction and amplifies the sound by a factor of 100 to 1,000. Thanks to the outer hair cells, our hearing sensitivity is increased by 40-60 dB (decibels). Notably, in the higher frequency ranges.
SO WHAT CAUSES THE RINGING?
When the outer hair cells put energy back into the vibration, it’s called positive feedback or “saturation feedback”. The process is meant to amplify very quiet sounds more so than loud ones. Most of the time, it works great and you go on with your life, not noticing anything out of the ordinary. However, biological systems aren’t always flawless. Occasionally, the amplification level of one or more outer hair cells will go awry and as a result, the whole system will erupt into spontaneous oscillation.
When this occurs, it becomes audible to us (we hear it). We perceive it as a ringing in the ear, or “sudden-onset ringing tinnitus”. As with most of our biological systems, there are quite a few homestatic control mechanisms (negative feedback loops) which exist to correct the problem and get rid of the unpleasant oscillation.
Nerves whose job it is to tell the auditory nerve and/or hair cells to cut it out. It takes roughly 30 seconds for this mechanism to begin to do its thing and send the required messages which suppress the ringing. After the message is sent and received, the tinnitus percept begins to fade away. You can tell when this reaction has taken place as its often accompanied by a slight reduction in hearing sensitivity (like background or ambient noise we hear suddenly getting quieter), followed by a feeling of fullness in the ear. It usually takes about a minute for this process to fully complete.
Our ears are walking a tightrope in high winds. While want our ear’s gain turned up high to maximize our hearing, we also don’t want the spontaneous oscillations that come with the increased sensitivity. If you stop and think about it, it’s amazing that our regulatory mechanisms work well enough that ringing doesn’t happen more often. The human body is more amazing than we give it credit for.