THE HUMAN EAR, OHR DES MENSCHEN,1894...

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Vintage-Views Antique Prints and Maps :: Antique Prints :: Scientific :: Medicine :: THE HUMAN EAR, OHR DES MENSCHEN,1894 Original Antique Color Engraving

THE HUMAN EAR, OHR DES MENSCHEN,1894 Original Antique Color Engraving

The ear is the sense organ that detects sound. The vertebrate ear shows a common biology from fish to humans, with variations in structure according to order and species. It not only acts as a receiver for sound, but plays a major role in the sense of balance and body position. The word "ear" may be used correctly to describe the whole vertebrate ear, or just the visible portion. In most animals, the visible ear is a flap of tissue that is also called the pinna. The pinna may be all that shows of the ear, but it has only a tiny role in hearing and none at all in the sense of balance. The pinna pictured here is a human example. In people, the pinna is more often called the auricle. Vertebrates have a pair of ears, each one placed symmetrically on opposite sides of the head. That arrangement aids in the ability to balance and in the ability to localize sound. Audition is the scientific name for the perception of sound. Sound is a form of energy that moves through air, water, and other matter, in waves of pressure. Sound is the means of auditory communication, including frog calls, bird songs and spoken language. Although the ear is the vertebrate sense organ that recognizes sound, it is the brain and central nervous system that "hears". Sound waves are perceived by the brain through the firing of nerve cells in the auditory portion of the central nervous system. The ear changes the pressure of sound waves from the outside world into a signal of nerve impulses sent to the brain. The outer part of the ear collects sound. That sound pressure is amplified through the middle portion of the ear and, in land animals, passed from a medium of air into a medium of fluid. The change from air to fluid occurs because air surrounds the head and is contained in the ear canal and middle ear, but not in the inner ear. The inner ear is hollow, heavy bone- the very heaviest bone of the body. The hollow channels of the inner ear are filled with fluid, and lined by a sensory epithelium that is studded with hair cells. The microscopic "hairs" of these cells are structural protein filaments that project out into the fluid. The hair cells are mechanoreceptors that release a chemical neurotransmitter when stimulated. Sound waves moving through fluid push the filaments, if the filament moves over enough it causes the hair cell to fire. In this way sound waves are transformed into nerve impulses. In vision, the rods and cones of the retina play a similar role with light as the hair cells do with sound. The nerve impulses travel from the left and right ear to both sides of the brain stem and up to the portion of the cerebral cortex dedicated to sound. This auditory part of the cerebral cortex is in the temporal lobe. The part of the ear that is dedicated to sensing balance and position also sends impulses through the eighth cranial nerve, the VIIIth nerve's Vestibular Portion. Those impulses are sent to the vestibular portion of the central nervous system. Although the sensation of hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear, human deafness (extreme insensitivity to sound) most commonly occurs because of abnormalities of the inner ear, rather than the nerves or tracts of the central auditory system.

Published for Joseph Meyer Meyers Konversations

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SKU	0527699k6
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Price:	US$50.00

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