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Definition of Ear
Ear definition - medical term
The hearing organ. There are three sect ions of the ear, according
to the anatomy textbooks. They are the outer ear (the part we see along the sides
of our head behind the temples), the middle ear, and the inner ear. But in terms
of function, the ear has four parts: those three and the brain. Hearing thus involves
all parts of the ear as well as the auditory cortex of the brain. The external ear
helps concentrate the vibrations of air on the ear drum and make it vibrate. These
vibrations are transmitted by a chain of little bones in the middle ear to the inner
ear. There they stimulate the fibers of the auditory nerve to transmit impulses
to the brain.
The outer ear
looks complicated but it is the simplest part of the ear.
It consists of the pinna or auricle (the visible projecting portion of the ear),
the external acoustic meatus (the outside opening to the ear canal), and the external
ear canal that leads to the ear drum. In sum, there is the pinna, the meatus and
the canal. That's all. And the external ear has only to concentrate air vibrations
on the ear drum and make the drum vibrate.
The middle ear
consists of the ear drum (the tympanum or tympanic membrane)
and, beyond it, a cavity. This cavity is connected via a canal (the Eustachian tube)
to the pharynx (the nasopharynx). The Eustachian tube permits the gas pressure in
the middle ear cavity to adjust to external air pressure (so, as you're descending
in a plane, it's the Eustachian tube that opens when your ears "open").) The middle
ear cavity also contains a chain of 3 little bones (ossicles) that connect the ear
drum to the internal ear. The ossicles are named (not the Nina, the Pinta and the
Santa Maria but) the malleus, incus, and stapes. In sum, the middle ear communicates
with the pharynx, equilibrates with external pressure and transmits the ear drum
vibrations to the inner ear.
The internal ear
is highly complex. The essential component of the inner
ear for hearing is the membranous labyrinth where the fibers of the auditory nerve
(the nerve connecting the ear to the brain) end. The membranous labyrinth is a system
of communicating sacs and ducts (tubes) filled with fluid (the endolymph). The membranous
labyrinth is lodged within a cavity called the bony labyrinth. At some points the
membranous labyrinth is attached to the bony labyrinth and at other points the membranous
labyrinth is suspended in a fluid (the perilymph) within the bony labyrinth. The
bony labyrinth has three parts: a central cavity (the vestibule), semicircular canals
(which open into the vestibule) and the cochlea (a snail-shaped spiral tube). The
membranous labyrinth also has a vestibule which consists of two sacs (called the
utriculus and sacculus) connected by a narrow tube. The utriculus, the larger of
the two sacs, is the principal organ of the vestibular system (which informs us
about the position and movement of the head). The smaller of the two sacs, the sacculus
(literally, the little sac) is connected with a membranous tube in the cochlea containing
the organ of Corti. It is in the organ of Corti that are situated the hair cells,
the special sensory receptors for hearing.
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