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SENSORY SYSTEM
Part 2
Lecture for medical students
Organs of Hearing,
Equilibrium
and
Taste
Department of histology,
cytology and embryology KhNMU
Organ of Hearing and Equilibrium
is located in the ear.
• Ear consists of:
• External ear – receives the sound waves
• Middle ear – transmits vibrations of
tympanic membrane
• Inner ear = labyrinth – contains receptors
for hearing and equlibrium
External, Middle, Inner Ear
External Ear
Auricle, external auditory meatus, tympanic membrane
(individual)
(ceruminous glands, earwax)
( fibrous membr. mucous inner)
Middle Ear
is the tympanic cavity in the temporal bone,
• contains ossicles: malleus, incus, stapes
Middle Ear
•
•
•
•
is the air space
bony ossicles are connected with joints
malleus is connected with ear drum
stapes closes the oval window,
leading to the inner ear
Middle Ear
is connected with nasopharynx by
eustachian tube
Middle Ear. Auditory (Eustachian)
tube
auditory
tube
Inner ear = labyrinth
is located in the temporal bone,
contains cochlea (organ of hearing),
vestibule and semicircular canals (organ
of equilibrium)
Inner Ear
Vestibule, semicircular canals, cochlea
Inner ear = Bony labyrinth
• is fillled with perilymph
• (similar in ionic content to extracellular fluid)
• in it is located:
• Membranous labyrinth is filled with
endolymph
• (similar to intracellular fluid)
Section of
the inner
ear
C
SC
V
Cochlea (C), vestibule (V), semicircular canal (SC).
Cochlea
The bony cochlea has
at its center the bony
pillar - modiolus (M)
containing spiral nerve
ganglion (G).
Bony canal does 2-3
spiral turns around
modiolus.
SV
SM
Sl
ST
G
M
G
SV
One section of
the coclea
spiral canal
VM
CD
Limbus
OC
Sl
n
S lig
BM
ST
Vestibular membrane (VM) and basilar
membrane (BM) divide canal into
scala vestibuli (SV),
cochlear duct (CD) and
scala tympani (ST).
m
SV
VM
CD
BM
ST
Coclear
duct
is three
angular
VAS
VM
OC
Limbus
S lig
BM
SL
The lateral wall of the cochlear duct is
formed by the stria vasculrias (vas), which
produces endolymph.
Stria
vascularis
Within the stria
vascularis you can
see capillaries (c),
an unusual feature
of this epithelium.
vas
c
SV
VM
CD
One section of
the spiral canal
Limbus
OC
Sl
n
S lig
BM
ST
m
Organ of Corti (OC) is on the basilar
membrane.
It is peripheral part of organ of hearing
Organ of
Corti
OC
TM
OHC
Limbus
IHC
On the osseous spiral lamina locates limbus
from which extends the tectorial membrane (TM)
Organ of
Corti
OC
TM
OHC
Limbus
IHC
Under the tectorial membrane locate the three rows of
outer hair cells (OHC) – columnar shaped.
The single inner hair cell (IHC) is seen medial - pear
shaped.
Organ of
Corti
OC
OHC
tm
sl
IHC
phc
High mag.
bm
pc
t
bsl
At the centre of OC the pillar cells (pc) form tunnel (t).
Hair cells are supported by phalangeal cells (phc).
Organ of Corti
tectorial membrane
outer hair cells
inner h.c.
outer phalanger cells
pillar cells
inner ph.c.
H
SV
At the top of the cochlear
canal the
scala vestibuli connects
with the
scala tympani -
CD
ST
G
Helicotrema
M
G
Helicotrema
SV
CD
ST
Scala vestibuli ends with the oval window,
scala tympani with the round window,
located in between middle and inner ear
oval window
cochlear duct
round window
Spiral
ganglion
G
The basal parts of hair cells
synapse with dendrites of
afferent n. cells of the spiral
ganglion, locating in the
osseous spiral lamina,
extending from the modiolus.
Mechanism of hearing:
under sound tympanic membrane vibrates, ossicles
push oval window.
Mechanism of hearing:
perilymph moves through helicotrema to round window, calls movement of
endolymph of cochlear duct and tectorial membrane which irritates hair cells.
Dendrites of spiral ganglion cells take impulse.
cochlear duct
The fibers of the basilar
membrane are the
shortest at the basal turns
– percept high-frequency
sounds.
H
SV
CD
ST
- are the longest at the
apical turns –
percept low-frequency
sounds.
G
SV
M
Inner hair cells percept
weak sounds, outer intense sounds.
G
Pathology
• Hearing loss:
• Otosclerosis
conductive
sensorineural
Ogran of
equilibrium
bsc
AC
Semicircular
canal
endolymph
Utricle
M
Vestibule
Perilymph
Semicircular canals and vestibule. Perilymph, endolymph.
Within the ampullated end of the bony semicircular canal (bsc) is
the ampullary crest (AC).
The flat macula (M) is in the utricle and saccule of the vestibule.
Inner Ear
Vestibule, semicircular canals, ampulla
Ampullary crest in the
semicircular canals
sc
The sensory epithelium (E) of the crest
has kinocilia and stereocilia and sits
on a mound of CT (ct) with nerves (N)
leading from it.
The crest has a gelatinous cupula (C)
resting on top of its receptor(E).
Function:
AC
C
E
ct
N
Ampullary crest in the semicircular
canals
• Movements of
endolymph causes
the deflection of the
cupula and
arisement of nerve
impulse
• Cells are stimulated
by movements of a
head and angular
accelerations
Macula of the
utricle and
succule
M
Utricle with macula
The macula (M) is a flattened collection of sensory hair cells
sitting upon their supportive cells.
The kinocilium and stereocilia of each sensory cell are
embedded in a gelatinous layer with calcified otoliths (arrow) –
otolith membrane.
Macula of the utricle and succule
O
R
S
A higher magnification of the edge of the macula showing the
otolithic layer (O) resting on a gelatinous layer (light arrow) atop
the sensory receptor (R) and supporting cells (S).
Macula of the utricle and succule gives
information about the force of gravity, linear acceleration and
static position of a head – turning, inclination, or in the dark,
under the water
(Pathology -Vertigo – the sence of rotation without equilibrium)
Otolith
membrane
Hair
cells
Supp.cells
Nerve
endings
The membranous labyrinth develops from ectodermal
first branchial grooves with contact of neural tube.
The vesicles are lined by pseudostraqtified epithelium
Differentiation of inner ear from otic
vesicle
Bony labyrinth and connective tissue develop from
mesenchyme. Nerve supply develops from neural
tube
Organ of Taste
• There are taste buds in the epithelium of
the tonque papillae.
• There are 4 taste sensations: sweet, biter,
acid and salty
cv
Papillae of
the tongue
ve
tb
low
• Tongue. Dorsal surface
• Each papilla contains many oval taste buds (tb) on the lateral
surfaces.
• Each taste bud is opened with taste pore
Taste bud
fp
tb
• Tongue, papilla with taste buds
high
med
There are 3 types of cells in taste bud:
1. basal are stem cells,
2. elongated supporting cells
3. actual taste cells.
Taste cells are also elongated cells whose microvilli extend into the taste pore
which opens to the surface; these cells are contacted by sensory nerves
from below.
Taste sensations
• Tip of the tongue - sensitive to sweet and
salt
• Lateral edges
- sensitive to sour
• Posterior portion - sensitive to bitter