ANATOMY AND PHYSIOLOGY
OF THE EXTERNAL EAR,
MIDDLE EAR AND
INNER EAR
Prof. Alexander I. Yashan, MD, PhD
EXTERNAL, MIDDLE AND THE
INTERNAL EAR
1 - external auditory
meatus;
2 - Pinna;
3 – ossicles (malleus;
incus; stapes) and
tympanic membrane;
4 – labyrinth (vestibule
semicircular canals
cochlea);
5 – tympanic cavity;
6 - auditory (acoustic)
nerve;
7 – arteria carotis;
8 - Eustachian tube
Is composed of a skin-covered cartilaginous
lamella whose posterior surface is evenly
convex and smooth, while its anterior
surface is concave, with semilunar folds and
hollows
between
them.
The
free
anteroexternal margin of the pinna is known
as the helix; towards the bottom the pinna
gradually turns into the lobe devoid of
cartilage and consisting of well-developed
fat and cellular tissue with a small number of
vessels and nerves. The small protuberance
of cartilage projecting over the external
auditory meatus is named the tragus. In
front of the helix and parallel to it is a ridge
known as the an thelix, with the antitragus
at its posterior end.
The skin on the anterior surface of the pinna
adheres directly to the perichondrium; on
the posterior surface, however, it may form
folds owing to the presence of a small layer
of loose cellular tissue.
PINNA
External Ear
• Auricle - framework of elastic
cartilage covered by skin
• Ear canal - about 3,5 cm
long, consists of outer
cartilaginous part and inner
bony part
• The cartilaginous part is
curved and lies at an angle
to the bony part, it also
narrows medially - ear drum
is protected from trauma
Removing of Round shaped
Foreign body
Tympanic Membrane
(eardrum)
1 – umbo;
2 - handle of malleus; (3)
(6) anterior and posterior
malleus folds;
4 - Pars flaccida or
Shrapnell's membrane;
5 - short process of
malleus;
7 – pars tensa;
8 – light reflex
Interconnected Auditory Ossicles
1 - malleus handle;
2 - head and neck of
malleus;
3- Malleus-incudal joint;
4- body of incus
5 - short process of incus;
6 - long process of incus;
7 - head of stapes;
8 – base of stapes;
9 - cruses of stapes
Anatomy of Middle Ear
Lateral wall
Middle Ear – 3 compartments
• The tympanic cavity is a small chamber,
about 1 cm3 in size, lying in the depth of
the temporal bone, between the tympanic
membrane and the internal ear.
• In front, through the Eustachian tube, the
tympanic cavity communicates with the
nasopharynx;
• behind, through the entrance into the
mastoid antrum (aditus ad antrum
mastoideum), communicates with the
latter and the cells of the mastoid Process.
TYMPANIC CAVITY
• It is customary to divide the into three
parts:
• the middle and biggest part,
mesotympanum, corresponding to the
pars tensa of the drum
• the upper part, epitympanum, lying above
the former and also known as the
epitympanic recess or attic;
• the lower part, hypotympanum, lying
below the drum level.
Epitympanum
• Lies above the
level of the short
process of the
malleus
• Contents:
– Head of the
malleus
– Body of the incus
– Associated
ligaments and
mucosal folds
Mesotympanum
• Contents:
–
–
–
–
Stapes
Long process of the incus
Handle of the malleus
Oval and round windows
• Eustachian tube exits from the
anterior aspect
• Two recesses extend posteriorly that
are often not visible directly
– Facial recess
• Lateral to facial nerve
• Bounded by the fossa incudis superiorly
• Bounded by the chorda tympani nerve
laterally
– Sinus tympani
• Lies between the facial nerve and the
medial wall of the mesotympanum
Hypotympanum
• Lies inferior and
medial to the
floor of the bony
ear canal
• Irregular bony
groove that is
seldom involved
by cholesteatoma
TYMPANIC CAVITY 6 WALLS
1.
2.
3.
The roof of the tympanic cavity is a thin plate
of bone separating the tympanic cavity from
the middle cranial fossa where the temporal
lobe is situated. This plate often has congenital
fissures through which vessels pass from the
middle cranial fossa. These anatomical
features may account for the meningeal
symptoms frequently observed in young
children with acute otitis media.
The internal wall separates the tympanic
cavity from the internal ear. It is marked by a
gentle eminence, the promontory
(promontorium), corresponding to the basal
turn of the cochlea. Above and behind the
promontory is an oval window or the fenestra
vestibuli (oval window) which leads into the
vestibule and is closed by the foot plate of the
stapes. Upwards Facial Nerve is situated.
Behind and below the promontory in a niche is
a round window or the fenestra cochlea
(round window) which leads into the cochlea,
and is filled with a thin membrane, the
secondary tympanic membrane.
External wall - tympanic membrane (Eardrum)
1.
2.
3.
The inferior wall or floor of the tympanic cavity is
separated from the jugular bulb by a fairly thick bony
plate. Bone fissures in this wall are rarely found.
The Eustachian tube begins with an opening in the
anterior wall separating the tympanic cavity from the
internal carotid canal.
An opening in the upper part of the posterior wall
leads to the mastoid antrum (aditus ad antrum
mastoideum).
TYMPANIC MUSCLES
• There are two muscles in the tympanic cavity:
• (1) The tensor tympani muscle which stretches
the tympanic membrane. It lies in the bony canal
above the Eustachian tube, and is attached to
the handle of the malleus.
• (2) The stapedius muscle which arises from the
posterior wall of the tympanic cavity and is
attached to the head of the stapes by a slender
tendon. The tensor tympani is innervated by a
branch of the trigeminal nerve, and the stapedius
muscle by a branch of the facial nerve.
Medial Wall
Eustachian or auditory tube
• About 3.5 cm in length connects
the tympanic cavity with the nasopharynx. The upper third of this
tube, adjoining the tympanic cavity,
has bony walls, while the remaining
lower portion leading into the
nasopharynx is made up of
membrane and cartilage.
• The movement of the cilia of the
ciliated epithelium lining the
Eustachian tube is towards the
nasopharynx.
• At rest, the Eustachian tube is in a
collapsed state, but with each
swallowing movement it opens by
contraction of the soft palatal
muscles attached to it, to let air into
the tympanic cavity.
• Is located just behind the external auditory
meatus is a bony structure protruding
downwards with the sternocleidomastoid
muscle attached to it. In young children, the
mastoid process is not fully developed and
represents a bony tubercle behind the osseous
tympanic ring.
• The antrum communicates with the tympanic
cavity and the air-filled cells of the mastoid
process. The superior wall or roof of the antrum
separates it from the middle cranial fossa.
• The following types of structure are to be found
in the mastoid process: the pneumatic or largecelled,
• diploic ". In the case of pneumatic structures,
the cavity of the mastoid process is divided by
thin bony partitions into a lattice of larger and
smaller cells. The diploic structure has tiny cells
resembling a diploetic bone;
• the most frequent is the mixed form of mastoid
structure where smaller cells are to be found
alongside bigger ones. In compact structures
the bone is indurated and the cells are very few;
this structure frequently occurs as a result of
MASTOID
PROCESS
Temporal bone & Inner Ear
(Labyrinth)
Bony Part: SemiCircular Canals, Vestibule, Cochlea
SC ducts, Utricle, Saccule
Membranous
Part
Choclear membranes
Internal Ear or Labyrinth
• (1; frontal semicircular
canal; (4) ampulla of frontal
semicircular canal; (3) apex
of cochlea; (4) medial turn of
cochlea; (5) apical turn of
cochlea; (6) basal turn of
cochlea; (7) round window;
(8) oval window; (9) ampulla
of sagittal semicircular
canal; (10) sagittal
semicircular canal; (11), (12)
crura; (13) ampulla of
horizontal semicircular
canal; crus commune of
frontal and sagittal semicircular canals
VESTIBULE (VESTIBULUM)
• The) lies in the centre of the bony labyrinth on whose
external wall is the oval window;
• on the opposite, internal wall, there are two recesses for
the two membranous sacs of the vestibule.
• The front sac known as the saccule (sacculus)
communicates with the membranous cochlea lying before
the vestibule, while the rear sac or utricle (utriculus) is
connected with the three membranous semicircular
canals passing behind and above the vestibule.
• The intercommunicating sacs of the vestibule contain the
statokinetic receptors or maculae acusticae,
• otolithic organs made up of a highly-differentiated
specific neuroepithelium covered with a membrane
containing granules of carbonate and phosphorate of
lime, i.e. the otoliths
SEMICIRCULAR CANALS
• The are set at right angles to each other and represent the
three planes of space.
• They are three in number: the external or horizontal, the
superior or frontal, and the posterior or sagittal. One end
of each canal opens out into a larger space known as
ampulla, the other end is even. The frontal and sagittal
canals have a common even stem (crus commune).
• The ampulla of each membranous canal contains a ridge.
• the crista ampullaris, which is a receptor, i.e. a nerve
ending consisting ot a highly-differentiated
neuroepithelium or hair and supporting cells.
• The free surface of the hair cells is covered with hairs
which respond to the slightest displacement or pressure of
the endolymph.
• The receptors of the vestibule and semicircular canals are
the peripheral nerve endings of the vestibular analysator.
COCHLEA
Modiolus the external wall and also turning
round the former, divides the tube lumen into
two directions, the upper or scala vestibuli
and the lower or scala tympani which
communicate at the apex of the cochlea
through a small opening known as the
helicotrema. Both channels are filled with
perilymph. The scala vestibuli communicates
with the vestibule, while the scala tympani
borders on the tympanic cavity through the
round window covered by the secondary tympanic membrane.
The scala vestibuli of the cochlea contains
the thin Reisner's membrane which extends
from the osseous spirn lamina to cut off a
small membranous canal of trianguli section
filled with endolymph and known as the
cochles duct or ductus cochlearis.
ORGAN OF CORTI
• (1) basilar
membrane: (2)
tectorial membrane;
(3), (4) hair cells; (5)
supporting cells; (6)
nerve fibres
reaching hair cells
Mechanism of
Hearing
• External ear “collects” the
sound
• Ossicles vibrate in the airfilled environment,
magnifying the sound and
aiming it to the oval
window
• The cochlea converts a
mechanical stimulus into
an electrical one
• The message is
transported to the brain by
the VIII-th nerve
Pure Tone Audiometry
• Audiometry is the precise method of hearing assessment. It is
performed in
a soundproof compartment by an audiologist, who uses an audiometer to
introduce measured sound intensities of selected tones to the listener,
usually through earphones. Pure tone thresholds are the minimal
intensities
of given tones (frequencies) that can be heard by the person being
tested. These thresholds are usually recorded on a grid, to create an
audiogram. This one has no responses recorded on it and is
presented purely to give an idea of the frequencies and loudness of
common sounds.
On this graph, the vertical axis plots hearing level (HL) in decibels (dB),
tiny units of loudness. These two abbreviations are usually used together
(dB HL) to report a patient’s test results or to refer to the level of loudness
of a given tone. Zero dB HL is near the top of the graph; this level is
barely
audible to a human with “perfect hearing.”