Diseases of the External Ear (Including Step-by-Step Otoplasty) SK Kaluskar
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Evolution of External EarCHAPTER 1

Almost 350 million of terrestrial evolution have produced variety of ear architecture which includes mammal. When one looks at the evolution of the ear, it is clear that there are many different designs of the vertebrate ears.
Since the appearance of the mammalian over 70 million years ago, it is apparent that there must have been ongoing important improvements in the design and abilities of hearing function. This is illustrated by the fact that ultrasonic hearing abilities of bats and whales, and the spectacular hearing sensitivity of the cat and primates.
The structure of the human inner ear is a consequence of selective pressures throughout mammalian and pre-mammalian evolution. The hearing mechanisms used by birds, reptiles, and placental mammals differ on fossil studies.
Animals with small heads also need to detect sounds at higher frequencies. This produces a detectable interaural difference in sound intensity. Directional clues was 2enhanced by skin folds around the ear canal and these folds must have become the outer ear (pinna). As It is known in lower animals i.e., cats and dogs have significant movement of the pinna muscles to direct towards the source of the sound. This “gathering the sounds” function of the pinna has been somewhat lost in human beings.
In a mammalian ear, such as bat's outer ear come in different sizes and shapes. The shape of outer ear of mammals varies across species. However, the inner workings of mammalian ears (including humans') are very similar.
The multiple ridges on the inner surface of the outer ear of some mammalian ears help to sharply focus echolocation signals, and any sound produced by the prey. These ridges can be regarded as the acoustic equivalent of a frenzel lens, and may be seen in a large variety animals such as the bat.
The ear begins to develop some eighteen days in a human embryo before the brain has become a complete organ. A group of surface cells on each side of the head begins to dimple. Each one of these groups forms a hollow sphere of cells in the shape of a bubble as it moves into the substance of the head. These cells forms the various parts of the ear.
The human ear is a sensory organ both of hearing and balance. The balance apparatus appears to have evolved prior to the hearing mechanism. Early developing vertebrates such as fish have organs of balance, but no cochlea.
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Embedded under the skin of a fish, along the length of its head and body, is a series of depressions. Groups of hair cells just beneath the grooves detect differences in water pressure, which allows the fish to adjust to variations in currents and eddies, and to warn against the proximity of other fish, including predators. At the beginning of life in the oceans, even the most primitive fish possessed this simple sense organ.
Over a period of time, the depressions in the head evolved into the structure of the inner ear found in all vertebrates, including humans. It is easy to imagine that nerve cells in the inner ear are adaptations of earlier hair cells sensitive to the motions of liquid.
During the course of evolution, fish became more amphibious, and finally developed into pure land animals. On the land, they required a new kind of sense organ which could detect slight differences in air pressure as a means of increasing their survival, such as recognizing food, danger, friends and enemies.
It is likely that the middle ear and the Eustachian tube evolved from the respiratory apparatus of the fish, while various inner ear structures were developed from parts of the fish jaw.
The external ears have also been ornamented with jewelry for thousands of years, usually by piercing of the earlobe. In some cultures, ornaments are placed to stretch and enlarge the earlobes.
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Earwax, also known as cerumen, is a yellowish waxy substance secreted in the ear canal of humans and other mammals. It protects the skin of the human ear canal, assists in cleaning and lubrication, and also provides some protection from bacteria, fungi, insects and water. Excess or impacted cerumen can occlude the external auditory canal and can impair hearing.
Wax is produced in the outer third of the cartilaginous portion of the human ear canal. It is a mixture of viscous secretions from sebaceous glands and less-viscous ones from modified apocrine sweat glands. The main components of earwax are shed layers of skin, with 60% of the earwax consisting of keratin, 12–20% saturated and unsaturated long-chain fatty acids, alcohols, and 6–9% cholesterol. Certain factors such as fear, stress and anxiety results in increased production of earwax from the ceruminous glands.
There are two distinct genetically determined types of earwax: the wet type, which is dominant, and the dry type, which is recessive. While Asians and Native Americans are more likely to have the dry type of cerumen, which is gray and flaky where as African and European people are more likely to have the wet type, which is honey-brown to dark-brown and moist.
Normal cleaning of the ear canal occurs as a result of the “conveyor belt” process of epithelial migration, aided by jaw movement. Cells formed in the center of the tympanic membrane migrate outwards from the umbo to the walls 5of the ear canal, and move towards the entrance of the ear canal. The cerumen in the canal is also carried outwards, taking with it any dirt, dust, and particulate matter that may have gathered in the canal. Jaw movement assists this process by dislodging debris attached to the walls of the ear canal, thus increasing its expulsion.
More recent studies have shown that ear wax has a bactericidal effect on some strains of bacteria. Wax has been found to reduce the viability of a wide range of bacteria, including Haemophilus influenzae, Staphylococcus aureus, and several variants of Escherichia coli, sometimes by as much as 99%. The growth of fungi commonly present in otomycosis was also significantly inhibited by human cerumen. These antimicrobial properties are due principally to the presence of saturated fatty acids, lysozyme and the slight acidity of wax with pH around 6.1 in normal individuals.
The treatment of ear wax was described by Aulus Cornelius Celsus in De Medicina in the first century 30 AD.
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