The human ear

Ears are a pair of intricate miniaturised organs. This is so because the various parts of the ear are packed into a very small space. Ears bring about the sensation of hearing. What is visible outside is simply a flap of tissue on the side of the head. This is the outer ear and helps gather sound.

The hearing process consists of the sound vibrations being converted to signals that can be carried to the brains. Here they get interpreted and the sound being heard becomes meaningful. This entire process is carried out in stages by very intricate inner ear parts that are not visible to us. The whole process is truly fascinating.

First of all because the inner ear parts are so delicate, there has to be a mechanism to protect them. Next, there has to be a mechanism to convert the vibrations that travel through air, or water or our bones and muscles into signals that can be sent to the brain for processing. Hence each part of the inner ear has a very specific task assigned to it.

Protector
If you put your finger into your ear, you can feel an opening at the end. This is actually the beginning of a three-centimetre long canal that runs obliquely inward. The canal is not straight because the delicate inner parts of the ear need to be protected. The non-straight canal makes it difficult for any object to reach inside. The canal also helps in warming the air in the ear to keep it cozy. If it gets very cold inside, as for example during very cold winter days, you would have experienced a dull pain in your ears. A, profusion of hairs in the canal and about 4000 wax glands help in trapping dust and small insects that can cause irritation in the ears. The wax also guards against infection, particularly when swimming in dirty water. In short, the inside of the ear must be clean and dust free. The canal achieves this efficiently.

Initiator of the hearing process
At the end of the canal is the eardrum. The eardrum is a tough, tightly stretched membrane less than two centimetres across. The hearing process starts here. The vibrating air brought in through the canal strikes the eardrum. Even slight vibrations caused for example from a whisper can make the eardrum vibrate. Even if the eardrum is pushed inward by only about a billionth of a centimeter, it is sufficient to cause a series of events resulting finally in the sound being interpreted.

Sound amplification
Just beyond the eardrum, are three tiny bones hinged together. These are called the anvil, hammer and Stirrup(also known as the stapes) because they vaguely resemble those things. It is their job to amplify the tiny movements of the eardrum. The tiny bones together amplify the vibrations about 22 times. This should give you a fair idea of how you can hear whispers and very faint sounds. The anvil is attached to the eardrum and the stirrup is attached to a thin membrane called the oval window. The amplified vibrations are passed on further inside the ear through this membrane.

Sound detection
Beyond the oval window is a fluid filled chamber. The sound detecting part of the ear is situated here. This is a snail-shaped cochlea. The interiors of the cochlea are studded with thousands of microscopic hair like nerve cells. When vibrations reach here, through the oval window, the fluid in the cochlea is set into vibrations and the hair like nerve cells are disturbed. Each nerve cell is sensitive to a particular vibration and hence to a particular sound. This makes it possible to distinguish different sounds. The disturbed nerve cell produces a signal (a tiny amount of electricity), which is then passed on to the auditory nerve. The auditory nerve, having a diameter of the order of a pencil leads into the brain. Thousands of electrical messages (signals) are passed on to the brain. The brain's job is to unscramble these data and convert them into meaningful sound.