Download The Ear, Moore 4th ed

The Ear, Moore 4th ed. pp. 962-976
External Ear
Auricle - is the outer part of the ear, made of cartilage and skin.
Parts:
Concha - is the innermost depression, the one that the tip of the
upper curve of the ear curves into.
Antihelix is the ridge outside the concha. It ends above in two
crura, and below in the antitragus which is the ridge over the
bottom part of the concha.
Scapha is the dent outside the antihelix, the thing that curves
under the outer edge of the ear.
Helix is the outer formation - the ridge around the ear that sits
above the scapha.
Tragus is the piece in front - the little bump.
Lobule is, well, the lobule.
Arterial Supply is the posterior auricular and superficial temporal arteries.
Nerve Supply is from the great auricular nerve to the area below the external
acoustic meatus, and the auriculotemporal nerve from CN V3 to the skin
above the opening.
Lymph drainage from above, outside goes to the superficial parotid lymph
nodes, and the medial surface of the upper part goes to the mastoid and
deep cervical nodes. The lobule drains to the superficial cervical lymph
nodes.
External Acoustic Meatus is the opening that goes inward to the inner parts of the ear.
It continues through the tympanic part of the temporal bone, to the tympanic
membrane, which is about 2-3 cm deep in adults. One-third, outside, is
still cartilage, while the inner 2/3 are bony, covered by a thinner skin that
is continuous with the tympanic membrane. There are subcutaneous
glands that produce earwax.
The tympanic membrane is about 1 cm around, and is the border between the
external acoustic meatus and the tympanic cavity of the middle ear. It is a
very thin skin outside, and the inside is mucous membrane. It dips in, the
base of the dip being the umbo, which bounces light back like a parabola.
(Important when looking in an ear - the cone of light.)
Divisions:
Flaccid part - the upper part without fibers. It forms the
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lateral wall of the superior recess of the tympanic
cavity on the inside.
Tense part - has radial and circular fibers.
There are ridges and bumps due to the malleus bone pressing on
it. The Posterior mallear fold comes off the top, to bend again
in the anterior mallear fold, where the malleus sticks out its
lateral process and handle to the point of the umbo.
Innervation: the auriculotemporal nerve, and a small auricular
branch of the vagus on the external skin side of the tympanic
membrane, and the glossopharyngeal on the inside.
The membrane works by vibrating to air and moving the ossicles in the
middle ear, which pass the message to the internal ear.
Middle Ear
It is found in the petrous part of the tympanic bone and contains the tympanic cavity, the epitympanic recess,
and the chorda tympani nerve of CN VII.
The tympanic cavity is an air chamber with the auditory ossicles. Its walls are:
Tegmental Roof - the tegmen tympani is a thin bony plate that separates the
cavity from the dura that is in the middle cranial fossa.
The Floor is the jugular wall, a layer of bone that separates the cavity from
the IJV about where it meets the sigmoid sinus.
The lateral (membranous) wall is the tympanic membrane and slightly
above, the bone of the epitympanic recess.
The medial (labyrinthinine) wall separates the tympanic cavity from the
internal ear. It is a slight mucosa over the promontory of the basal turn of
the cochlea. The mucosa contains part of the tympanic nerve and plexus.
The carotid (anterior) wall separates the cavity from the carotid canal, and
has the internal carotid running against it on the outside. It is bony, but at
the top of the wall has the pharyngotympanic (auditory) tube opening and
a canal for tensor tympani muscle.
The posterior (mastoid) wall has an opening at the upper part which is called
the aditus which connects the cavity to the mastoid cells. The facial nerve
canal descendes between the posterior wall and the antrum, medial to the
aditus.
The Mastoid Antrum
Is a cavity in the mastoid process of the temporal bone, and separated from
the middle cranial fossa by the tegmen tympani, a small bony wall
(continued from over the roof of the tympanic cavity).
The facial nerve canal runs under it.
Its floor communicates with the mastoid cells through small openings.
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It is lined by mucous membrane.
It can get infected via an ear infection and lead to bone infection.
Mastoid cells -
Auditory Ossicles form a chain of bones from the tympanic membrane to the oval window,
which is an opening in the medial wall of the cavity that leads to the vestibule of the inner
ear. The malleus is the end of the chain attached to the tympanic membrane, and the stapes
blocks the oval window hole. They are covered with mucous membrane but not periosteum.
Malleus - functions as a lever with anterior and lateral processes. The anterior
process and the handle are attached to the membrane.
The superior head lies in the epitympanic recess. It articulates
with the incus.
The neck dents into the flaccid part of the tympanic membrane.
The handle is embedded in the tympanic membrane and moves
with it. The tensor tympani muscle has a tendon that inserts
into the handle near the neck.
Incus
The body is in the epitympanic recess and attaches to the head of
the malleus.
The long limb process lies parallel to the handle of the malleus
and attaches to stapes through a projection - the lenticular
process.
The short limb process is connected to the back wall of the cavity.
Stapes
The head attaches to the incus.
Two crura make a horseshoe type shape to attach to the base.
The base fits into the oval window. It is much smalle than the
tympanic membrane, so the vibratory force is amplified on it.
The auditory ossicles increase the force of vibrations while
reducing the amplitude.
Muscles with the Ossicles dampen movement.
Tensor tympani arises from the superior cartilage part of the
pharyngotympanic tube, the greater wing of the sphenoid, and the petrous
part of the temporal bone, and inserts into the handle of malleus. It pulls
the handle inward, which tightens the tympanic membrane and reduces
the amplitude of its movements. It protects from too much vibration in
loud sounds and is supplied by the mandibular nerve.
Stapedius is inside the pyramid of the back wall of the tympanic cavity. It
gives off a tendon that passes through a small foramen and attaches to the
neck of stapes. It pulls stapes back and tips it in the oval window, which
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reduces the oscillatory range. It filters sound this way. If it is paralyzed
(CN VII) there is an excessive enhancement of hearing.
Pharyngotympanic Tube - connects the tympanic cavity (through a hole in the front wall) to the
nasopharynx. One-third laterally is bony and the rest is cartilage. It is lined by mucous
membrane that is continous with the tympanic cavity’s and also the nasopharynx’s.
It equalizes pressure between the middle ear and the atmosphere! This is
important so the tympanic membrane can 1. move and 2. not explode. It
is normally closed, but opens by the action of the contracted levator veli
palati muscle pressing against one wall of cartilage, while the tensor veli
palati pulls the other. (Swallowing, yawning, pop the eardrums.)
The arteries of the tube are:
Ascending pharyngeal artery which is a branch of the external
carotid.
Maxillary artery:
Middle meningeal branch
Artery of pterygoid canal branch.
Veins drain into the pterygoid venous plexus
Nerves come from the tympanic plexus which come from
Facial nerve
Glossopharyngeal nerve
Fibers from pterygopalatine ganglion
The Internal Ear
Bony Labyrinth fills the otic capsule, a piece of dense bone that surrounds it - it is fulled with
fluid.
Cochlea is the shell shaped part with the cochlear duct. Its spiral canal
begins at the vestiblue and wraps around the modiolus, a bony core
containing canals for blood vessels and the cochlear nerve. The outermost
turn (basal) of the cochlea produces the promontory - an indentation seen
on the inner wall of the tympanic cavity. There is a cochlear aqueduct on
the basal side that opens the bony labyrinth to the subarchnoid space near
the jugular foramen. The cochlea is divided into:
Cupula - the point inside where the spiral starts
First turn
Second turn
Vestibule is a small chamber containing the utricle and saccule.
Oval Window is a spot on the lateral wall, where the stapes
attaches.
It opens through the aqueduct of the vestibule to the posterior
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cranial fossa. It extends to the posterior part of the petrous part
of the temporal bone and opens. It transmits the
endolymphatic duct and two blood vessels.
It has three recesses, the elliptical, the cochlear, and the spherical
(from top to bottom). They have perforations for nerve fibers.
The Semicircular Canals communicate with the vestibule. They open five
times into the vestibule (not 6 - the ant. and post. share one
opening).Each has one swollen end, the ampulla. There are three,
occupying 3 planes:
Anterior
Posterior
Lateral
The Membranous Labyrinth is the set of sacs and ducts inside the bony labyrinth. It is filled
with endolymph, instead of perilymph which is in the bony part. It is suspended in the bony
labyrinth, not free. There are two divisions, the cochlear labyrinth and the vestibular
labyrinth.
Spiral ligament is a thickening of the periosteal lining and secures the
cochlear duct to the spiral canal of the cochlea.
The semicircular ducts open into the utricle through five holes. The utricle
communicates with the saccule through the utriculosaccular duct, from
which the endolymphatic duct arises. The saccule communicates with the
cochlea through a uniting duct.
The endolymphatic duct runs through the bone of the posterior cranial fossa
and comes out in a blind pouch - the endolymphatic sac, which stores
extra fluid.
Vestibular Labyrinth
Utricle and Saccule have sensory epithelium. The areas in which
it is found are called the maculae. These cells attach to the
vestibulocochlear nerve. The sensory neurons are in the
vestibular ganglia in the internal acoustic meatus.
Semicircular Canals contain the semicircular ducts, which have
ampullae at one end. The ampulla contain sensory ampullary
crests that record movement. The cell bodies of these neurons
are in the vestibular ganglia.
Cochlear Duct is the spiral tube inside the cochlea. It is held in place by the
spiral ligament and the osseous spiral lamina of the modiolus. The duct
divides the canal into two channels, communicating at the helicotrema,
the open space at the inner end of the spiral. The pressure from the stapes
pass through the scala vestibuli, one of the channels, wrap around through
the helicotrema, and continue back around the spiral outwards through
the scala tympani, the other channel. At the end, it vibrates the round
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cochlear window, which is closed by the secondary tympanic membrane.
The organ of Corti is the auditory receptive part, situated on the inside of
the duct on the basilar membrane (floor of the duct) and overlaid by the
tectorial membrane.
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