5-6. THE EXTERNAL EAR
The external ear begins on the outside of the head in the form of a funnel-shaped
auricle (pinna). Actually serving as a funnel, the auricle directs airborne sound waves
into the external auditory meatus. The external auditory meatus is a tubular canal
extending into the temporal portion of the skull
5-7. THE MIDDLE EAR
a. Tympanic Membrane. At the inner end of the external auditory meatus is a
tympanic membrane. The tympanic membrane (eardrum) is a circular membrane
separating the external auditory meatus from the middle ear cavity. The tympanic
membrane vibrates (mechanically oscillates) in response to airborne sound waves.
b. Middle Ear Cavity. On the medial side of the tympanic membrane is the
middle ear cavity. The middle ear cavity is a space within the temporal bone.
c. Auditory Ossicles. The auditory ossicles (OSSICLE = small bone) are three
very small bones which form a chain across the middle ear cavity. They join the
tympanic membrane with the medial wall of the middle ear cavity. In order, the ossicles
are named as follows: malleus, incus, and stapes. The malleus is attached to the
tympanic membrane. A sound stimulus is transmitted from the tympanic membrane to
the medial wall of the middle ear cavity by way of the ossicles. The ossicles vibrate
(mechanically oscillate) in response to the sound stimulus.
d. Auditory (Eustachian) Tube. The auditory tube is a passage connecting the
middle ear cavity with the nasopharynx. The auditory tube maintains equal air pressure
on the two sides of the tympanic membrane.
e. Association With Other Spaces. The middle ear cavity is associated with
other spaces in the skull. The thin roof of the middle ear cavity is the floor of part of the
cranial cavity. The middle ear cavity is continuous posteriorly with the mastoid air cells
via the antrum (an upper posterior recess of the middle ear cavity.
5-8. THE INTERNAL EAR
a.
Labyrinths (Figure 5-4).
(1) Bony labyrinth. The bony labyrinth (LABYRINTH = a maze) is a complex
cavity within the temporal bone. It has three semi-circular canals, a vestibule (hallway),
and a snail-shaped cochlear portion.
(2) Membranous labyrinth. The membranous labyrinth is a hollow tubular
structure suspended within the bony labyrinth.
MD0805
5-9
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