Define the Structure of Ear - The Organ of Hearing

The human ear consists of three sections: the outer ear, the middle ear and the inner ear as illustrated in Figure. The outer ear includes the auricle (pinna), the visible part of the ear that is attached to the side of the head, and the waxy, dirt- trapping auditory canal. The tympanic membrane (eardrum) separates the external ear from the middle ear, an air-filled cavity. The part of the ear, which we can see, is only a small and rather unimportant part of the ear, and is called the external ear or the pinna. The visible part, or the pinna, is a small appendage on our face, as can be seen in Figure. It is commonly thought to collect the sound waves and funnel them.

But at least in human beings where the pinna is rather small, it is unlikely that this function is significant. Experiments have been conducted in which the various depressions of the external ear have been filled with a plasticine-like material to obliterate them. It has been found that doing so, makes no difference to the efficiency of hearing. Even in animals with large pinnae, a far more important function of these structures is to help in the localization of sound. By moving the ears, such experiments can accentuate the difference in the intensity of the sound reaching the two ears, and thereby localize sound more accurately. Since human beings cannot move their ears, they cannot use the pinnae very efficiently for this purpose. For accentuating the difference in the intensity of sound reaching the two ears, they turn the whole head instead of turning just the ears. The direction from which a sound is coming is judged from the difference in the time at which the sound arrives at the two ears, and the difference in the intensity of the sound at the two ears.