Unilateral tinnitus (a ringing in one ear only) that doesn't go away is probably something you should talk to an audiologist about. Occassional ringing in one ear is normal and harmless.
To understand why it happens, you need to know a bit about how the ear turns vibration (from sound) into electrical signals in the brain (that you hear). The mammalian cochlea has two types of sensory hair cell - inner hair cells and outer hair cells - which convert movement into an electrical signal. When a sound arrives at your ear, the pressure fluctuations in our inner ear fluids vibrate a long, spiral trampoline-like structure called the basilar membrane. Movement of this membrane is detected by the inner hair cells (which sit on top of it), and they in turn send signals to the brain via the auditory nerve.
However, the whole structure is suspended in the salty water of the inner ear, which reduces its ability to move in response to sound (if you've ever tried to run in water you'll know that it's more difficult than running in air - there's much more friction due to the viscosity of the water). That's where the outer hair cells come in. Like the inner hair cells, they also detect movement of the basilar membrane (called "mechanoelectrical transduction"), but unlike the inner hair cells they are also capable of vibrating themselves ("electromechanical transduction").
Rather than send lots of signals to the brain, their job is to contract and expand in time with the vibration they detect, thereby cancelling-out the friction. This increases the size of the vibration by a factor of 100-1000 (like being on a swing and kicking your legs at just the right time) and this improves your hearing sensitivity by between 40 - 60 dB, particularly in the high frequencies.
Putting energy back into this vibration is called "positive feedback". In this case, it's actually "saturation feedback" because it's nonlinear - the process amplifies very quiet sounds much more than loud ones. Usually it works pretty well and everybody's happy, but being a biological system, things aren't perfect.
Occasionally the gain (amplification level) of one or more outer hair cells will become a bit too high and the system will burst into spontaneous oscillation. This may be audible to us as a sudden-onset ringing tinnitus in one ear.
And being a biological system, there are various homestatic control mechanisms (negative feedback loops) that exist to fix the problem and get rid of the oscillation. These include various efferent nerves from the brain whose job it is to tell the hair cells and/or auditory nerve to turn it down a bit. It takes them about 30 seconds for this loop to get into gear and send the messages that suppress the ringing, over which time the tinnitus percept slowly fades away.
It often sounds like it's accompanied by a slight reduction in hearing sensitivity (like the background static noise we hear suddenly gets quieter), and a feeling of fullness in that ear, but it's usually back to normal in about a minute.
It's a tightrope really - you want the ear's gain turned up high enough to maximize your hearing, but not so high as to cause spontaneous oscillations. Frankly, it's a tribute to these regulatory mechanisms that it doesn't happen more often.
To understand why it happens, you need to know a bit about how the ear turns vibration (from sound) into electrical signals in the brain (that you hear). The mammalian cochlea has two types of sensory hair cell - inner hair cells and outer hair cells - which convert movement into an electrical signal. When a sound arrives at your ear, the pressure fluctuations in our inner ear fluids vibrate a long, spiral trampoline-like structure called the basilar membrane. Movement of this membrane is detected by the inner hair cells (which sit on top of it), and they in turn send signals to the brain via the auditory nerve.
However, the whole structure is suspended in the salty water of the inner ear, which reduces its ability to move in response to sound (if you've ever tried to run in water you'll know that it's more difficult than running in air - there's much more friction due to the viscosity of the water). That's where the outer hair cells come in. Like the inner hair cells, they also detect movement of the basilar membrane (called "mechanoelectrical transduction"), but unlike the inner hair cells they are also capable of vibrating themselves ("electromechanical transduction").
Rather than send lots of signals to the brain, their job is to contract and expand in time with the vibration they detect, thereby cancelling-out the friction. This increases the size of the vibration by a factor of 100-1000 (like being on a swing and kicking your legs at just the right time) and this improves your hearing sensitivity by between 40 - 60 dB, particularly in the high frequencies.
Putting energy back into this vibration is called "positive feedback". In this case, it's actually "saturation feedback" because it's nonlinear - the process amplifies very quiet sounds much more than loud ones. Usually it works pretty well and everybody's happy, but being a biological system, things aren't perfect.
Occasionally the gain (amplification level) of one or more outer hair cells will become a bit too high and the system will burst into spontaneous oscillation. This may be audible to us as a sudden-onset ringing tinnitus in one ear.
And being a biological system, there are various homestatic control mechanisms (negative feedback loops) that exist to fix the problem and get rid of the oscillation. These include various efferent nerves from the brain whose job it is to tell the hair cells and/or auditory nerve to turn it down a bit. It takes them about 30 seconds for this loop to get into gear and send the messages that suppress the ringing, over which time the tinnitus percept slowly fades away.
It often sounds like it's accompanied by a slight reduction in hearing sensitivity (like the background static noise we hear suddenly gets quieter), and a feeling of fullness in that ear, but it's usually back to normal in about a minute.
It's a tightrope really - you want the ear's gain turned up high enough to maximize your hearing, but not so high as to cause spontaneous oscillations. Frankly, it's a tribute to these regulatory mechanisms that it doesn't happen more often.
