otometrics Madsen ZODIAC 901, Руководство пользователя

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Middle Ear The middle ear is an air-filled cavity (the tympanic cavity) connected to
the throat, and thence to the atmosphere, by a fine channel, the Eusta-
chian Tube, which serves to prevent the build-up of a pressure differen-
tial across the ear-drum. The healthy Eustachian Tube is normally
obstructed except during swallowing.
Auditory Ossicular
Chain In the middle-ear cavity is a structure of three tiny bones—hammer ( mal-
leus ), anvil ( incus ) and stirrup ( stapes )—called the auditory ossicular
chain, which links the ear-drum to another membrane, the oval window
(
fenestra vestibulii ovalis ). Among the attachments between the auditory
ossicular chain and the walls of the middle ear is a tendon connecting
the stirrup to a tiny muscle, the
stapedius muscle. The hammer is also
subject to the action of a muscle, the tensor tympani . When either or both
of these two muscles contract, the ear-drum to becomes tensioned, and
the impedance of the system will be increased.
Inner Ear The oval window is the component by which sound waves enter the in-
ner ear, in the form of mechanical vibrations. The inner ear (labyrinth) is
filled with fluid, and consists of the cochlea, which converts the vibra-
tions into nerve impulses, and the semi-circular canals, which form part
of the body’s balancing mechanism.
The auditory ossicular chain serves as a broad-band impedance-
matching transformer.
8.6 THE EFFECT OF LOUD SOUNDS
The normal condition of the ear-drum is that of a highly compliant
membrane which has only a small influence on the impedance presented
to acoustic waves travelling through the outer ear. The main constituent
74 Operation Manual
PRINCIPLES OF MIDDLE-EAR ANALYSIS
Chap. 8 GN Otometrics
THE EFFECT OF LOUD SOUNDS
8.6 ZODIAC 901 Middle-Ear Analyzer
Fig.8.1
Section through the ear