2. - The external ear consists of the auricle and the
external acoustic meatus. Sound waves in the air are
transmitted to the eardrum of the middle ear.
- The middle ear starts from the tympanic membrane,
the epitympanic recess, and the ossicles – malleus,
incus, and stapes. The ossicles sense the vibrations
of the sound waves on the tympanic membrane,
converting and amplifying the energy into mechanical
energy, which travels into the inner ear. Note the
auditory, or Eustachian, tube connecting the middle
ear to the nasopharynx, which allows the equilibration
of pressure.
- The inner ear consists of 1) the cochlea for auditory
sense and 2) the semicircular ducts, ampullae,
utricle, and saccule for the sense of balance and
position. The membranous labyrinth is found within the
bony labyrinth.
3. - Note the handle, or manubrium, of the malleus
(commonly known as the hammer) firmly attaches to
the upper half of the tympanic membrane. The head of
the malleus contacts the incus.
- The incus, or anvil, body articulates with the head of
the malleus. The long process or limb of the incus
descends vertically, parallel to the handle of the
malleus, and contacts the stapes.
- The stapes, or commonly known as the stirrup, head
articulates with the incus. The two crura or limbs
diverge and join at the flattened oval base, which
attaches to the oval window.
- Via the three ossicles, vibrations are transmitted from
the tympanic membrane to the oval window and to the
inner ear, which will be discussed later.
- Note the other structures within the tympanic cavity of
the middle ear. The tensor tympani muscle inserts
into the handle of the malleus and dampens vibrations
of the tympanic membrane.
- The stapedius muscle may not be visible, but its
tendon attaching to the stapes may be seen. It acts to
dampen vibrations of the stapes.
- Note the facial nerve (CN VII) within the facial canal,
making an almost 90 degree turn to exit the
stylomastoid foramen. It gives off the greater petrosal
nerve from the geniculate ganglion. Note also the
chorda tympani coming off the facial nerve and
traveling between the long limb of the incus and
malleus handle.
4. - Shown here is the view of the tympanic membrane
through an otoscope. Note most of the eardrum has a
strong fibrous layer that provides rigidity; this area is
called the pars tensa. The upper one-sixth of the
tympanic membrane lacks this fibrous layer and is
termed the pars flaccida. The manubrium of the
malleus attaches firmly on the tympanic membrane
and can be seen. The cone of light from the otoscope
can be seen inferior and anterior to the manubrium.
Together, they look like an arm bending at the elbow.
- As mentioned before, the inner ear specializes in
auditory sense and sense of balance and
equilibrium.
- The cochlear nerve provides auditory sense from the
cochlea, the spiral-shaped organ that receives the
vibrations from the oval window and converts them to
nerve impulses.
- The vestibular nerve receives input from the
semicircular ducts, the utricle, and the saccule. The
semicircular ducts detect angular acceleration. The
utricle and saccule detect linear acceleration.
- The cochlear and vestibular nerves join together as
CN VIII, the vestibulocochlear nerve.
- Note once again the facial nerve (CN VII) traveling in
close proximity to CN VIII and making a sharp bend
near the tympanic cavity. Note also the geniculate
ganglion, the greater petrosal nerve, and the chorda
tympani.
5. -The inner ear is located in the petrous part of the
temporal bone. Both the tympanic cavity and bony
labyrinth are found here. Within the bony labyrinth is
the membranous labyrinth.
- The bony labyrinth contains perilymph (high Na+, low
K+), while the membranous labyrinth has endolymph
(high K+, low Na+).
- The inner ear is composed of the following:
- semicircular ducts (anterior, posterior, and
lateral) with associated ampullae
- the utricle
- the saccule
- the cochlea
- Review: The tympanic membrane transmits vibrations
through the ossicles to the oval window. The
vibrations then enter the inner ear and are detected by
specialized cells in the cochlea. The round window
acts as a release valve for the vibrations.
- Note in the bottom panel the organization of the
cochlea. The cochlear duct contains the organ of Corti
and three compartments – the scala vestibuli, the scala
media, and the scala tympani – all of which will be
detailed in the following slide.
- The cell bodies of cochlear neurons, or spiral
ganglia, wrap around the modiolus of the cochlea.
Their axons come together as the cochlear nerve
found in the center of the modiolus.
6. - The 3 membranous tubes of the cochlea are shown at
higher magnification:
- scala vestibuli – perilymph
- scala media (cochlear duct) – endolymph
- scala tympani – perilymph
- The scala vestibuli and scala media are separated by
the vestibular (Reissner’s) membrane. The scala
media and scala tympani are separated by the basilar
membrane, which is not a basement membrane but
instead includes the organ of Corti.
- The basilar membrane oscillates in response to
various frequencies transmitted from the oval window.
Low frequency sounds vibrate near the apex of the
cochlea, while high frequency is sensed near the base.
- Note the 3 outer hair cells (labeled 1, 2, 3) with
apical stereocilia displaced by the tectorial membrane
when the basilar membrane vibrates. The reticular
lamina is a rigid plate of cytoplasm that prevents
abnormal displacement of the stereocilia and
subsequent depolarization. The hair cells are
supported by phalangeal cells.
- The inner and outer pillar cells are filled with
microtubules to provide a rigid, triangular inner tunnel.
This remains rigid to allow the organ of Corti to rock
back and forth, instead of collapsing on itself by the
vibrations.
- Inner hair cells are found as a single row near the
7. - Within the bony vestibule, we find the utricle and the
saccule of the membranous labyrinth. It is very difficult
to identify one from the other without seeing
surrounding structures. The utricle is closer to the
semicircular ducts, while the saccule is closer to the
cochlea. The utricle and saccule are filled with
endolymph, while the surrounding vestibule with loose
connective tissue contains perilymph.
- Both the utricle and saccule contain a neurosensory
area known as the macula. This consists of hair and
supporting cells overlaid by a gelatinous otolithic
membrane covered with otoliths or otoconia.
Displacement of the otolithic membrane moves the
stereocilia of the hair cells, allowing the maculae to
sense linear acceleration.
8. - The three semicircular ducts are oriented in 3
perpendicular planes. This allows detection of angular
acceleration. At the origin of each semicircular duct
near the utricle, there are ampullae. Each one of these
dilations has a crista ampullaris projecting into the
lumen.
- The thickened sensory epithelium at the tip of the
crista contain many neurosensory cells with stereocilia,
which is similar to the macula. The hair cells insert into
the cupula, which is a gelatinous material similar to the
otolith membrane but lacking any otoliths. The cupula
shown in the bottom right appears dehydrated.
- Like other parts of the inner ear, the membranous
part of the semicircular duct contains endolymph while
the bony part contains perilymph.
9. EAR, HEARING & BALANCE
In the inner ear are the organs for the senses of hearing
and balance - the cochlea and the vestibular apparatus
The outer and middle ear get airborne sound to the
inner ear.
Most of the balance information provided is not ‘sensed’,
but ‘balance‘ will do to get us started
The signals are turned into nerve-cell electrical activity
by mechanoreception for sensing fluid movement
so we shall start with this idea in lower animals that
need to know what water currents are around them and
how they are moving in relation to the water.
Then we’ll see how sensing the movement of special
fluid in the vestibular apparatus informs on how the
head is positioned and is moving
10. The ‘HAIRS’ of HAIR CELLS
Thus far, we have spoken of hairs as they
were known to microscopists for the first half
of the last century.
The electron microscope revealed that each
‘hair’ consists of one kinocilium at the side of
an array of many non-motile sensory
stereocilia. (These stereocilia are not the
absorptive kind found in the male repoductive tract.)
A cell - View from on top
Cilium
Viewed from the side, the
stereocilia differ regularly
in height, becoming
shorter going away from
the tall kinocilium
They are more numerous
than shown (70 per cell),
and are attached by links
near their tips
Stereocilia
11. HAIR-CELL DIRECTIONAL SENSITIVITY
Kinocilium
Viewed from the
side, the stereocilia
vary regularly in
height, becoming
shorter going away
from the tall
kinocilium
Stereocilia
Sensitive to bending:
Tip links
between
stereocilia
Plate for
attachment of
actin cores of
stereocilia
Vesicles &
tubules
Afferent axon
Synapse
Towards kinocilium
causes cell
depolarization, and
increased afferent
fiber firing
Bending away from
kinocilium causes cell
hyperpolarization, and
decreased afferent
fiber firing
12. CUPULA
The bending of the hairs sometimes is coordinated and amplified by imbedding the
hairs in a gelatinous body called the cupula
CANAL FLUID
CUPULA
HAIR CELLS
13. HAIR-CELL SIGNAL TRANSDUCTION
Kinocilium
How does bending towards kinocilium
cause cell depolarization, and increased
Stereocilia
afferent fiber firing?
Tip links
between
stereocilia
Transduction channels
for cations, e.g., Ca2 +, K+
are opened by the bending
The entering cations
depolarize the cell
Vesicles &
tubules
Synapse
which increase s transmitter
release at the base,
raising the firing rate in
the axon
14. Supporting, basal, mantle, etc cells
Electron microscopy also revealed that the
‘supporting’ cells were of various different
kinds
Certain of the supporting cells secrete the
gelatinous (glycoprotein) cupula
Nerve fibers and synapses were both afferent,
and coming from the CNS as effferent
(controlling)
Afferent synapses were of more than one kind,
as are the hair cells
Although there was a fundamental pattern,
species differences were widepsread in ‘hairs,
sensory cells, ‘supporting’ cells, and almost all
aspects of the receptor structures
15. VESTIBULAR APPARATUS I
Spaces form in the skull’s temporal
bone on each side for three differently
oriented CANALS communicating with
a larger space - VESTIBULE - to hold a
system of fluid-filled bags & tubes
The fluid in the bags - endolymph has a special ionic composition to
allow for efficient depolarization,
when the hair-cell stereocilia are
deflected.
Each canal, and the hair cells
positioned within it, provide nervous
signals responsive to movement of
the head in a particular way.
The three mutually perpendicular
canals on each side can thus inform
on any angularly accelerated (rotary)
head movement
16. VESTIBULAR APPARATUS II Semicircular canal & duct
BONE
SEMICIRCULAR CANAL containing
Perilymph
SEMICIRCULAR DUCT containing
Endolymph
Always an initial source of confusion - the semicircular space
in the bone is the CANAL
Inside, and attached to the wall, is the smaller membranous tube the DUCT
The rest of the space in the canal is taken by a loose arachnoidlike tissue, occupied by CSF-like perilymph
The duct is filled with endolymph, high in K+,
& made elsewhere
When the head moves in the plane of the canal, the endolymph
lags a little in relation to the canal’s & duct’s movement
17. VESTIBULAR APPARATUS III Duct’s Ampulla & Christa
At one end of the canal, where it opens into the bony vestibule,
the duct swells out, then constricts, creating the ampulla
SEMICIRCULAR DUCT
BONE
ENDOLYMPH
Endolymph
CUPULA
SEMICIRCULAR
CANAL
Perilymph
AMPULLA
Raised ridge CRISTA - with hair
cells & gelatinous
cupula
Opening into utricle
18. VESTIBULAR APPARATUS IV Duct & Christa Activity
As th head moves so
, the endolymph in this duct lags
along with the cupula
SEMICIRCULAR DUCT
BONE
ENDOLYMPH
Endolymph
CUPULA
SEMICIRCULAR
CANAL
Perilymph
But moving with the
head are the tissues,
including the hair
cells
So the hair cells are
bent by the dragging
cupula
causing opening or
closing of the cation
channels, with
change in hair-cell
polarization &
synaptic drive
to the christa axons
19. VESTIBULAR APPARATUS V Saccule & Utricle
MACULA
of Utricle
Ampulla of superior
semicircular duct
start of superior
semicircular duct
UTRICLE
Utricular Duct
MACULA
of Saccule
SACCULE
SACCULE
Saccular
Duct
20. VESTIBULAR APPARATUS VI Saccule versus Utricle
Both contain endolymph & are connected via the U & S ducts
Both utricle & saccule contain a macula with hair cells
Both maculae are covered with a gelatinous otolithic membrane
MACULA
of Utricle
UTRICLE
but
The maculae are oriented differently
Saccule’s near vertical;
Utricle’s near horizontal
The utricle is much larger
Utricular Duct
The utricle has the six openings
for the 3 semicircular ducts
MACULA
of Saccule SACCULE
Saccular
Duct
21. VESTIBULAR APPARATUS VII Macula Structure
Endolymph
OTOLITHIC
MEMBRANE
Connective
tissue
Crystalline OTOCONIA
on gelatinous
OTOLITHIC
MEMBRANE
HAIR CELLS
Supporting cells
Basement membrane
AXONS of vestibular
ganglion neurons
Being in pairs, and in different orientations, the maculae
can sense the head’s position and its linear movement
The OTOCONIA of calcium salts and protein contribute to the effect
of gravity on the hair cells, providing a vestibular drive to eventually
keep ‘postural’ skeletal muscles active in maintaining one’s posture
22. VESTIBULAR APPARATUS VIII Vestibular nerve & Ganglion
Ampulla of
superior
semicircular
duct
CRISTA
start of superior
semicircular duct
The vestibular
ganglion & nerve
lie in the bony
internal acoustic
meatus
UTRICLE
Bipolar
neurons VESTIBULAR
NERVE
MACULA
of Utricle
MACULA
of Saccule
SACCULE
VESTIBULAR GANGLION
23. TEMPORAL BONY SPACES
We have seen that: the semicircular ducts require three
canals in each temporal bone; the utricle and ampullae,
& the saccule, need a vestibule in the bone; and the
vestibular ganglion & nerve need a passageway
(meatus) to reach the brainstem.
Also, within the bone, spaces must be found for the air
vibrations to be conveyed to the cochlea; while air
pressure has to be equilibrated across the ear drum
The cochlea has to have its own coiled space in the bone
Finally, passages (aqueducts) are needed to keep the
two fluids - perilymph and endolymph - in balance
The intricate result is best depicted initially as a crude
diagram for learning parts and relations
31. EAR, HEARING & BALANCE
In the inner ear are the organs for the senses of hearing
and balance - the cochlea and the vestibular apparatus
The outer and middle ear get airborne sound to the
inner ear.
The signals are turned into nerve-cell electrical activity
by mechanoreception for sensing fluid movement
so we shall start with this idea in lower animals that
need to know what water currents are around them and
how they are moving in relation to the water.
Having seen how sensing the movement of special fluid
in the vestibular apparatus informs on how the head is
positioned and is moving,
we can examine how sounds are sensed in the cochlea
32. COCHLEAR APPARATUS I
Spaces form in the skull’s temporal
bone on each side for three differently
oriented CANALS communicating with
a larger space - VESTIBULE - to hold a
system of fluid-filled bags & tubes
Also, coming off the vestibule is the
snail-like bony cochlea with 21/2 turns
The cochlear duct inside contains
endolymph , with a special ionic
composition to allow for efficient
depolarization, when the hair-cell
stereocilia are deflected.
The deflection arises from membrane
deflections, ultimately derived from air
vibrations outside the head
33. TEMPORAL BONY SPACES
We have seen that: the semicircular ducts require three
canals in each temporal bone; the utricle and ampullae,
& the saccule, need a vestibule in the bone; and the
vestibular ganglion & nerve need a passageway
(meatus) to reach the brainstem. (Other nerves pass by.)
Also, within the bone, spaces must be found for the air
vibrations to be conveyed to the cochlea; while air
pressure has to be equilibrated across the ear drum
The cochlea has to have its own coiled space in the bone
Finally, passages (aqueducts) are needed to keep the
three fluids - perilymph, endolymph, & CSF - in balance
The intricate result is best depicted initially as a
diagram for learning parts and relations, but first a more
anatomical overview of the whole system
37. COCHLEA III One turn - Compartments
BONE
Scala vestibuli
PERILYMPH
BONE
Scala tympani
Osseous
spiral lamina
PERILYMPH
Reissner’s
membrane
COCHLEAR
DUCT or
Scala media
ORGAN of
CORTI
Basilar
membrane
38. COCHLEA IV Bony Modiolus
HELICOTREMA
where Scalae
vestibuli & tympani
connect
The cochlea
spirals around a
bony core - the
Modiolus
Note that
although, in
a section, we
see five
profiles, the
structures
spiral
continously
e.g.,
OSSEOUS
SPIRAL
LAMINA
M
O
D
I
O
L
U
S
Scala vestibuli
COCHLEAR
DUCT or
Scala media
Scala
tympani
39. COCHLEA IV Spiral ganglion & Modiolus
The modiolus is very
spongy bone , filled with
nerve fibers becoming the
cochlear nerve
SPIRAL
GANGLION
ORGAN of
CORTI
Also, the VIIIth nerve
has incoming efferent
fibers to influence the
outer hair cells in the
Organ of Corti
’efferent’ - from
brain-stem neurons
Axons to Inner
hair cells derive
from spiralganglion cell
bodies
40. COCHLEA VI Basilar membrane I
Osseous
spiral lamina
BONE
Scala vestibuli
PERILYMPH
BONE
SPIRAL
LIGAMENT
STRIA
VASCULARIS
makes
endolymph
Scala tympani
PERILYMPH
The basilar membrane is tensed
between the osseous spiral lamina &
the spiral ligament
Basilar
membrane
41. COCHLEA VII Basilar membrane II
The spiralling hides that the basilar membrane is LONG
The basilar membrane is vibrated by fluid pressures in the Scala typani
Its WIDTH & STIFFNESS alter regularly along its length, so that
COCHLEAR
DUCT or
Scala media
BONE
Scala vestibuli
The high-frequency
response is at the base
The particular component
frequencies of a ‘sound’
produce a pattern of
vibrations along the basilar
membrane,
PERILYMPH
BONE
Scala tympani
PERILYMPH
Vibrations from oval
window of vestibule
It vibrates well to low
frequency sounds at its apex
ORGAN of
CORTI
detectable by the inner hair
cells attached to the active
regions of the
Basilar membrane
42. Tectorial membrane & Inner Hair Cell
TECTORIAL MEMBRANE is gelatinous, like the cupula, but is
attached at one side, aside from its hair-cell connections
Support for Reissner’s
membrane & Tectorial
membrane
TECTORIAL
MEMBRANE
with attached
ENDOLYMPH
SPIRAL LIMBUS
Scala
tympani
INNER HAIR CELL
innervated by axon
from spiralganglion neuron
Basilar
membrane
43. Organ of Corti - cell types
Crista & Macula -- “Electron microscopy also revealed that the
‘supporting’ cells were of various different kinds”. Far more true for
the Organ of Corti, and detectable already in the 19th century, hence
some eponyms
TECTORIAL MEMBRANE
TECTORIAL CELLS
INNER HAIR CELL
OUTER HAIR CELLS
SPIRAL LIMBUS
HENSEN &
CLAUDIUS
CELLS
Basilar membrane
INNER &
OUTER PHALANGEAL CELLS
DEITER’S
INNER & OUTER
PILLAR CELLS
44. Stria vascularis & K+ recycling I
The Kcc4 channel gets the K+ into the Deiter’s cells, whence it
goes via gap junctions to theStria for pumping into the endolymph
STRIA CELLS
FIBROBLASTS
OUTER HAIR CELLS
INNER HAIR CELL
K+
HENSEN &
CLAUDIUS
CELLS
Basilar membrane
INNER & OUTER OUTER PHALANGEAL CELLS
PILLAR CELLS
DEITER’S
45. Stria vascularis II
The Stria vascularis was so named because, quite unusually, capillaries
are found amongst the three kind of epithelial cells
STRIA CELLS
HENSEN &
CLAUDIUS
CELLS
Basilar membrane
46. SOUND CONDUCTION TO THE INNER EAR
We’ll return to the schematic of the whole auditory
system for:
The cochlea has to have its own coiled space in the bone
Also, within the bone, spaces must be found for the air
vibrations to be conveyed to the cochlea; while air
pressure has to be equilibrated across the ear drum
The membrane-sealed openings - oval & round windows
- from vestibule to middle ear, allowing transmission of
pressures, but keeping in the perilymph
The tympanic membrane (ear drum) separating outer
auditory meatus from the middle ear
51. AUDITORY OSSICLES II
OVAL WINDOW
VESTIBULE
ROUND WINDOW
To relieve fluid pressures
in the vestibule
STAPES
INCUS
MALLEUS
EXTERNAL
CANAL
EAR
MALLEUS
INCUS
STAPES
MIDDLE EAR
DRUM
The malleus (hammer) is vibrated by air impinging
on the tympanic membrane (ear-drum). Malleus
movements drive the incus (anvil), which in its
turn moves the stapes (stirrup) in and out of the
oval window, so pulsating the fluid (perilymph) in
the vestibule. The bony chain & geometry amplify
the air’s initial force.
52. AUDITORY OSSICLES II
OVAL WINDOW
VESTIBULE
ROUND WINDOW
To relieve fluid pressures
in the vestibule
STAPES
INCUS
MALLEUS
EXTERNAL
CANAL
EAR
MALLEUS
INCUS
STAPES
MIDDLE EAR
DRUM
The malleus (hammer) is vibrated by air impinging
on the tympanic membrane (ear-drum). Malleus
movements drive the incus (anvil), which in its
turn moves the stapes (stirrup) in and out of the
oval window, so pulsating the fluid (perilymph) in
the vestibule. The bony chain & geometry amplify
the air’s initial force (& match impedance)
53. AUDITORY OSSICLES III
The malleus (hammer) is vibrated by air impinging on the
tympanic membrane (ear-drum). Malleus movements
drive the incus (anvil), which in its turn moves the stapes
(stirrup) in and out of the oval window, so pulsating the
fluid (perilymph) in the vestibule. The bony chain &
geometry amplify the air’s initial force.
EAR DRUM
MALLEUS
INCUS
STAPES
OVAL WINDOW
54. Stapedius muscle & Facial nerve
Tympanic cavity/
Middle ear
FACIAL
NERVE
INCUS
the Stapedius muscle
whose contraction
hinders the
movement of the
STAPES so
protecting the ear
from loud sounds
along with Tensor
tympani‘s action (
Stapedius muscle
Oval
window
Other long spaces in
the bone house the
Facial nerve &
VESTIBULE
The two responses
constitute Sound
attenuation reflex
55. TENSOR TYMPANI
Tensor tympani muscle has its bony tunnel parallel to Eustachian tube’s
VESTIBULE
AURICLE
MIDDLE EAR
EAR CANAL
V th
NERVE
COCHLEA
Auditory TUBE
Malleus
Tensor tympani muscle TT tendon
TT contraction limits Malleus movement for protection from loud sounds
56. EMBRYOLOGY I
COCHLEA II
LININGS
BRAIN
CRANIAL
CAVITY
SEMICIRCULAR
CANALS
PERIOSTEUM
SACCULE
TS
UC
ED
QU
A
UTRICLE
VESTIBULE
Two chambers
connect
COCHLEA
MASTOID
AIR
CELLS
EXTERNAL CANAL
COCHLEA
MIDDLE
EAR
TEMPORAL BONE
EUSTACHIAN TUBE
Ductus reuniens
Note the TWO chambers for perilymph
with the Scala media in between
PERIOSTEUM
‘AIRWAY’
MENINGES
‘SKIN’
MUCOSA
COCHLEAR
DUCT or
Scala media
MEMBRANOUS
LABYRINTH
The linings are clues to the several structures involved in ear formation
The precursors of the linings sent signals to surrounding mesenchyme,
to construct structures to house what they themselves were engaged in
forming
57. Full-face view 4-w embryo
What is going on inside the cranial end of the
embryo? E.g., plans for Inner & Middle ear?
BRAIN
I
II
I
CORD
HEART
II
CARDIAC BULGE
Mid-sagittal section
58. Mid-sagittal section of 1-m embryo
PHARYNGEAL ARCHES
covered by ectoderm
PHARYNGEAL POUCHES
lined by endoderm
BRAIN
I II
Pouch pattern is more
complicated & does not
quite match arch pattern
Next slides will
schematize &
simplify floor of
Arches I-IV
59. Pharyngeal
groove I
PHARYNGEAL POUCHES: inside
for ear canal
Endodermal lining of
pharyngeal pouch
for Middle ear
ARCH
I
II
Endodermal lining of
pharyngeal pouch
III
IV
Ectodermal
covering
Mesenchymal core
makes, for instance, the ossicles
Arch cut into
60. SOURCES OF EAR LININGS
The linings are clues to the several structures involved in ear formation
PHARYNGEAL POUCHES
lined by endoderm
‘AIRWAY’
MUCOSA
of Middle ear
PHARYNGEAL ARCHES
covered by ectoderm
I II
BRAIN
‘SKIN’
of ear canal
Neural crest
MESECTODERM
Ectodermal
OTIC PLACODE
but lying
laterally
MEMBRANOUS LABYRINTH
MENINGES
PERIOSTEUM
but later, when
bone has formed
61. OTIC PLACODE Lens & Olfactory similar
OTIC PLACODE
BRAIN ECTODERM
Neural crest MESECTODERM
OTIC PLACODE’s rim rises, so
creating, then deepening the otic pit
in preparation for forming a vesicle
OTIC VESICLE is already defining upper
& lower parts of membranous labyrinth
U
L
62. OTOCYST SITE & DEVELOPMENT
7 weeks
Semicircular
Duct
5 weeks
Endolymphatic
duct
Utr
BRAIN
Utricle
Rhombencephalon
Sa
U
L
OTIC VESICLE/CYST
Mesenchyme
for OSSICLES
Ist PHARYNGEAL
CLEFT
TUBULO-TYMPANIC
RECESS
Cochlear
Duct
Sacc
Semicircular
Duct
64. SOURCES OF EAR LININGS
The linings are clues to the several structures involved in ear formation
Ectodermal
OTIC PLACODE
MEMBRANOUS LABYRINTH
PHARYNGEAL ARCHES
covered by ectoderm
PHARYNGEAL POUCHES
lined by endoderm
‘SKIN’
of ear canal
‘AIRWAY’
MUCOSA
OTIC VESICLE/
OTOCYST
Ist PHARYNGEAL
CLEFT
TUBULO-TYMPANIC
RECESS
of Middle ear
Neural crest
MESECTODERM
MENINGES
Neural crest
MESECTODERM
PERIOSTEUM
around cranial
NEURAL TUBE
BONES
65. 4-w/3.5mm EMBRYO
Full-face
Remains of FRONTONASAL
PROMINENCE after
development of nasal placodes
NASAL PLACODE
OPTIC PLACODE
MAXILLARY PROCESS
STOMODEUM
with perforating membrane
MANDIBULAR ARCH
HYOID ARCH
CARDIAC BULGE
FACE
67. EAR PATHOLOGY
Wax, foreign
Overgrowth of bone - Otosclerosis
bodies in canal
Excess endolymph - hydrops
Ankylosed ossicles
Meningitis,
FACIAL
abscess
NERVE
VIIIth
Angle tumor
NERVE
-Neuroma of
AURICLE
VIIIth N - bad
balance
/hearing
Lost Hair
cells - loud
noises, age,
streptomycin,
neomycin,
cisplatin
Blocked tube
V
EAR CANAL
COCHLEA
EAR DRUM
MIDDLE
EAR
CARTILAGE
Perforated ear-drum
-infection, blast injury
Eustachian TUBE
Otitis media - middle ear infection; Cholesteatoma - kerat strat squam ep
Nasopharynx Auditory/
68. EAR PATHOLOGY II
Lost/damaged Hair cells from - loud noises, age;
ototoxic agents - streptomycin, neomycin (aminoglycoside
antibiotics), cisplatin (anticancer agent)
Congenital deafness - One of a number of defects in genes can
impair the development of the inner ear, or the differentiation and
functioning of hair cells
Hypothyroidism and iodine deficiency in pregnancy can result in
defective development of the fetus’ Organ of Corti
69. EAR PATHOLOGY III
Overgrowth of bone Otosclerosis
Angle tumor -Neuroma
of VIIIth N - bad
Ankylosed
ossicles
Meningitis,
abscess
balance /hearing
Lost Hair cells - loud
noises, age, streptomycin,
Excess endolymph hydrops
Congenital deafness - defects in genes
Blocked Eustachian tube
Wax, foreign
bodies in canal
Otitis media - middle ear
infection
Perforated ear-drum
-infection, blast
