Encyclopaedia Britannica, 11th Edition, "Hearing" to "Helmond"

Encyclopaedia Britannica, 11th Edition, "Hearing" to "Helmond" - Volume 13, Slice 2

HEARING (formed from the verb to hear, O. Eng. hyran, heran, &c., a common Teutonic verb; cf. Ger. hren, Dutch hooren, &c.; the O. Teut. form is seen in Goth. hausjan; the initial h makes any connexion with ear, Lat. audire, or Gr. very doubtful), in physiology, the function of the ear (q.v.), and the general term for the sense or special sensation, the cause of which is an excitation of the auditory nerves by the vibrations of sonorous bodies. The anatomy of the ear is described in the separate article on that organ. A description of sonorous vibrations is given in the article Sound; here we shall consider the transmission of such vibrations from the external ear to the auditory nerve, and the physiological characters of auditory sensation. 1. Transmission in External Ear.The external ear consists of the pinna, or auricle, and the external auditory meatus, or canal, at the bottom of which we find the membrana tympani, or drum head. In many animals the auricle is trumpet-shaped, and, being freely movable by muscles, serves to collect sonorous waves coming from various directions. The auricle of the human ear presents many irregularities of surface. If these irregularities are abolished by filling them up with a soft material such as wax or oil, leaving the entrance to the canal free, experiment shows that the intensity of sounds is weakened, and that there is more difficulty in judging of their direction. When waves of sound strike the auricle, they are partly reflected outwards, while the remainder, impinging at various angles, undergo a number of reflections so as to be directed into the auditory canal. Vibrations are transmitted along the auditory canal, partly by the air it contains and partly by its walls, to the membrana tympani. The absence of the auricle, as the result of accident or injury, does not cause diminution of hearing. 123 In the auditory canal waves of sound are reflected from side to side until they reach the membrana tympani. From the obliquity in position and peculiar curvature of this membrane, most of the waves strike it nearly perpendicularly, and in the most advantageous direction. ......Buy Now (To Read More)

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Ebook Number: 39521
Author: Various
Release Date: Apr 23, 2012
Format: eBook
Language: English