1. Organs of Hearing, Equilibrium and Taste
SENSORY SYSTEM
Part 2
Lecture for medical students
Organs of Hearing, Equilibrium
and
Taste
Department of histology,
cytology and embryology KhNMU

2. 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

3. External, Middle, Inner Ear

4. External Ear Auricle, external auditory meatus, tympanic membrane (individual) (ceruminous glands, earwax) ( fibrous membr. mucous inner)

5. Middle Ear is the tympanic cavity in the temporal bone, malleus, incus, stapes
contains ossicles:

6. Middle Ear Middle Ear is connected with nasopharynx by eustachian tube
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

7. Middle Ear. Auditory (Eustachian) tube

8. Inner ear = labyrinth is located in the temporal bone,
contains cochlea (organ of hearing),
vestibule and semicircular canals (organ of equilibrium)

9. Inner Ear Vestibule, semicircular canals, cochlea

10. 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)

11. Section of the inner earSC V
Cochlea (C), vestibule (V), semicircular canal (SC).

12. Cochlea SV
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.
SM Sl ST G M G

13. One section of the coclea spiral canalSV
One section of the coclea spiral canal VM CD
Limbus
Sl n OC
S lig BM m ST
Vestibular membrane (VM) and basilar membrane (BM) divide canal into
scala vestibuli (SV),
cochlear duct (CD) and
scala tympani (ST).

14. SV CD ST VM BM

15. 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.

16. Stria vascularis
Within the stria vascularis you can see capillaries (c), an unusual feature of this epithelium.
vas c

17. One section of the spiral canalSV
One section of the spiral canal VM CD
Limbus
Sl n OC
S lig BM m ST
Organ of Corti (OC) is on the basilar membrane.
It is peripheral part of organ of hearing

18. Organ of Corti OC TM
OHC
Limbus
IHC
On the osseous spiral lamina locates limbus from which extends the tectorial membrane (TM)

19. 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.

20. Organ of Corti OC OHC tm sl IHC bm pc t bsl
phc bm
pc t bsl
High mag.
At the centre of OC the pillar cells (pc) form tunnel (t).
Hair cells are supported by phalangeal cells (phc).

21. Organ of Corti
tectorial membrane outer hair cells inner h.c outer phalanger cells inner ph.c pillar cells

22. At the top of the cochlear canal the scala vestibuli connects with the SV
At the top of the cochlear canal the
scala vestibuli connects with the
scala tympani - Helicotrema CD ST G M G

23. Helicotrema SV CD ST

24. 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

25. 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.

26. Mechanism of hearing:
under sound tympanic membrane vibrates, ossicles push oval window.

27. Mechanism of hearing: cochlear duct
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

28. - are the longest at the apical turns – percept low-frequency sounds.
The fibers of the basilar membrane are the shortest at the basal turns – percept high-frequency sounds.
- are the longest at the apical turns –
percept low-frequency sounds.
Inner hair cells percept weak sounds, outer - intense sounds. SV CD ST G SV M G

29. Pathology
Hearing loss: conductive
sensorineural
Otosclerosis

30. Ogran of equilibrium bsc
endolymph
bsc
Utricle AC
Semicircular canal
Vestibule M
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.

31. Inner Ear Vestibule, semicircular canals, ampulla

32. Ampullary crest in the semicircular canalssc AC
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: C E ct N

33. 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

34. Macula of the utricle and succule
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.

35. Macula of the utricle and succule
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).

36. 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

37. The membranous labyrinth develops from ectodermal first branchial grooves with contact of neural tube. The vesicles are lined by pseudostraqtified epithelium

38. Differentiation of inner ear from otic vesicle

39. Bony labyrinth and connective tissue develop from mesenchyme
Bony labyrinth and connective tissue develop from mesenchyme. Nerve supply develops from neural tube

40. Organ of Taste
There are taste buds in the epithelium of the tonque papillae.
There are 4 taste sensations: sweet, biter, acid and salty

41. cv Papillae of the tongue ve Tongue. Dorsal surface tb low
Each papilla contains many oval taste buds (tb) on the lateral surfaces.
Each taste bud is opened with taste pore

42. Taste bud fp tb Tongue, papilla with taste buds high med
There are 3 types of cells in taste bud: 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.
med

43. Taste sensations Tip of the tongue - sensitive to sweet and salt
Lateral edges sensitive to sour
Posterior portion - sensitive to bitter