• Structure of Human Ear

    Ears act as receiver or detector of sound. The sounds received in the form of pressure variations in air are converted into electrical signals within the ear which on reaching our brain produce a sense of hearing. The human ear can be considered to consist of the following three parts:



    Outer Ear: The outer ear looks complicated but it is functionally the simplest part of the ear. It consists of the ‘pinna’ or auricle (the visible projecting portion of the ear), the external acoustic meatus (the outside opening to the ear canal), and the external ear canal that leads to the ear drum. In sum, there is the pinna, the meatus and the canal. That's all. The outer ear concentrates air vibrations on the ear drum and makes the drum vibrate. The outer ear is also called the external ear.

    Middle Ear: The middle ear consists of an eardrum or tympanic membrane connected at the end of the auditory canal. The eardrum is a thin, tightly stretched membrane, also known as sheet (‘kaan ka parda’ in Hindi). The eardrum vibrates when compressions and rarefactions of sound wave hit it. A compression exerts an inward pressure on the outer surface of the eardrum. This forces the eardrum to move inward. However, a rarefaction does the opposite and moves the eardrum outwards. Hence, the eardrum is made to vibrate by the successive compressions and rarefactions.

    The vibration of eardrum produces pressure variations within the middle ear. The three bones (hammer, anvil and stirrup) present in the middle ear amplify these pressure variations by several times. The middle ear then transmits the sound wave’s amplified pressure variations to the inner ear.

    Inner Ear: The inner ear has a job to convert the sound wave’s amplified pressure variations into electrical signals. This work is done in the inner ear by cochlea, a snail-shaped organ. The cochlea is filled with a waterlike fluid and its inner surface has large number of hair-like nerve cells. The amplified pressure variations produce vibrations in the nerve cells and they in turn release electrical impulses. The electrical impulses are transmitted to the brain along the auditory nerve. The brain interprets the electrical impulses through a complex process, as sounds.