A complete lecture of Secondary Sentiment Sense Organs: The Ear, taught at First Moscow State Medical University, Moscow, in the Histology department, for the first year English medium foreign medical students.

1. Secondary Sentient Sense Organs
Organ of Hearing
Organ of Equilibrium
Organ of Taste
Lecturer – professor Boronikhina Tatiana Vladimirovna

2. Secondary sentient sense organs contain neuroepithelial
receptor cells
 Neuroepithelial cells form synapses with sensory neuron dendrites
 Neuroepithelial cells interact with stimuli
⇓
generate nerve impulses
⇓
transmit impulses to sensory neurons
dendrite
°°°°

3. Hearing Equilibrium Taste

4. Organ of hearing
 receptor field is the spiral organ or organ of Corti
 is housed in the cochlea of the inner ear
Cochlea ⇒

5. Inner ear is the bony labyrinth in the temporal bone
 Cochlea
 Vestibule

saccule

utricle
 Semicircular canals (3)
⇓
⇑
the temporal bone petrous portion

6. Bony labyrinth houses the membranous labyrinth
 bony labyrinth is filled with perilymph
 membranous labyrinth is filled with endolymph
⇑
 perilymph and endolymph communicate with CSF in the meningeal spaces

7. Inner ear receptor fields
 hearing and equilibrium receptor fields
⇒
 reside in the membranous labyrinth
 are bathed by endolymph
⇐

8. Cochlea
 has a broad base and apex
 is a bony tube that spirals 2.5 times around
⇓ the modiolus ⇒

9. Modiolus
 is osseous cochlea axis
 contains nerve fibers
 projects laterally into the spiral lamina
⇑
n. vestibulocochlearis (VIII)

10. Spiral lamina
 consists of two lips
 upper lip periosteum thickens to form
the spiral limbus
 contains the spiral ganglion
limbus
⇐ spiral ganglion
upper lip
⇓
lower lip

11. Cochlea passages
 Scala vestibuli
 Scala tympani
 contain perilymph
 Scala media (cochlear duct)
 contains endolymph
SG
Sv
St
Sm

12. Cochlear perilymphatic passages
 Scala vestibuli and scala tympani
⇓
⇑
communicate with each other
at the helicotrema

13. Scala vestibuli and scala tympani
associate with the middle ear
 Scala vestibuli
 ends at the oval window

is closed by the stapes ⇒
 stapes transmits vibrations to perilymph
 Scala tympani
• ends at the round window
• is closed by connective tissue membrane
auditory ossicles

14. Scala media is the cochlear membranous labyrinth
 Scala media walls
 vestibular membrane
 stria vascularis
 basilar membrane

15. Vestibular membrane
 extends between the spiral limbus and the cochlear wall
 separates the scala media from the scala vestibuli
 consists of two layers of endothelial cells
vestibular membrane

16. Stria vascularis
 consists of a pseudostratified epithelium

is vascularized by capillaries ⇒
 secretes endolymph and creates its high positive potential
 rests on the spiral ligament – thickened periosteum of the cochlear bone
stria vascularis
spiral ligament
⇐
⇐
⇐

17. Basilar membrane
 separates the cochlear duct from the scala tympani
 includes keratin-like fibrils – hearing cords
⇑
basilar membrane
• upper surface contains
the spiral organ
• low surface is lined with
endothelium

18. Basilar membrane fibrils vibrate with perilymph
 are slender and long near the cochlea apex
 vibrate in resonance with low-frequency sounds
 are thick and short near the cochlea base
 vibrate in resonance with high-frequency sounds

19. Spiral organ lies upon the basilar membrane
 Phalangeal cells (supporting)
 Hair cells (neuroepithelial)
 stereocilia (hair) are on the apical surface
 stereocilia are embeded in the tectorial membrane
 Pillar cells (supporting)
 enclose the tunnel filled with endolymph

20. Tunnel divides the spiral organ in the two cell groups
⇑
 Outer group is organized in three or more rows
outer phalangeal cells
outer hair cells
 Inner group is organized in a single row
⇐ inner phalangeal cells
inner hair cells
inner hair cell

21. Spiral organ inner group cells
 Inner phalangeal cells
 completely surround the hair cells
 Inner hair cells
 are bulbous in shape
 have stereocilia arranged in a straight line
⇓

22. Spiral organ outer phalangeal cells
 surround only the basal portion of hair cells

phalangeal processes form the cuticular plate ⇒

23. Spiral organ outer hair cells
 are columnar in shape

have stereocilia arranged in a V-formation ⇒

24. Scanning electron micrograph of the hair cell stereocilia
⇐ inner hair cells ⇒
⇐ outer hair cells ⇒

25. Spiral organ histology

26. Spiral organ innervation
 Sensory bipolar neurons are
in the spiral ganglion ⇒
 Afferent fibers
 are sensory neuron dendrites
 pass in the tunnel
 form light synapses on the hair cells
 Efferent fibers
 are the brain neuron axons
 pass in the tunnel
 form dark synapses on the hair cells

27. Spiral ganglion sensory neuron axons
⇑
form the cochlear division of
n. vestibulocochlearis (VIII)
pass in the modiolus
⇓

28. Hearing

sound waves transmit vibrations on ⇒ timpanic membrane ⇒ auditory
ossicles ⇒ oval window ⇒ perilymph ⇒ basilar membrane fibrils
⇓
spiral organ

29. Hair cells are mechanoreceptors
 nerve impulse generation results from stereocilia inclination
 microenvironment - endolymph
tectorial membrane
⇒
dendrite
°°°°°°°°
dendrite

30. Hair cell differentiation
Hair cells perceive
 in the cochlea base – high-frequency sounds
 in the cochlea apex – low-frequency sounds
 outer hair cells – high intensity sounds
 inner hair cells – low intensity sounds

31. Organ of equilibrium or vestibular apparatus
 receptor fields are the maculae and the cristae
 are housed in the vestibule and canals of the inner ear
⇐ vestibule and
semicircular canals

32. Equilibrium receptor field localization
 maculae (2) are in the saccule and utricle
 cristae (3) are in the ampullae of the semicircular canals
⇓

33. Vestibular macula and crista ampullaris
crista in the semicircular
canal ampulla ⇒
macula in the saccule
⇐

34. Macula structure
 supporting cells
 neuroepithelial hair cells
 otolithic membrane with otoliths

35. Crista structure
 supporting cells
 neuroepithelial hair cells
 cupula

36. Equilibrium neuroepithelial hair cells
 are innervated by afferent
and efferent fibers ⇒
 apical surface contains
50-100 stereocilia and
a single kinocilium ⇒

37. Equilibrium hair cell types
 Type I cells
 are bulbar in shape
 basal portion surrounded by
a cap-shaped nerve ending
 Type II cells
 are columnar in shape
 basal portion has bouton nerve ending
⇐
⇒

38. Vestibular apparatus innervation
 sensory neuron bodies are housed
in the vestibular ganglion ⇓
 their dendrites innervate hair cells of
maculae and cristae
 their axons form vestibular division of
n. vestibulocochlearis (VIII)
⇐
⇑

39. Equilibrium hair cells are mechanoreceptors
 nerve impulse generation results from stereocilia inclination
dendrites
microenvironment – endolymph
cupula
otolithic membrane with otoliths
dendrites
dendrite
°°°°

40. Equilibrium hair cell stereocilium inclination
⇑ ⇓
towards the kinocilium away from the kinocilium
cells become excited cells become inhibited

41. Equilibrium hair cell differentiation
 Maculae are sensors of
 linear accelerations
 gravity
 vibrations
 Cristae are sensors of
 angular accelerations
⇐
⇒

42. Organ of taste
 receptor field consists of the taste bauds
 taste buds are located on the lateral surface
of lingual papilae
⇐
tongue ⇒
dorsal surface

43. Lingual papillae are projections of the mucosa
on the tongue dorsal surface
Papilla structure:
 stratified squamous partially keratinized epithelium
 a central core (primary papilla) – LCT
 taste buds occupy the epithelium of the lateral papilla surface
⇓
⇑
taste bud is an ovoid
intraepithelial structure

44. Lingual papilla types
 filiform papillae are covered by keratinized epithelium
and lack the taste buds ⇒

45. Taste buds are epithelial structures
 epithelial cells are arranged around the taste pit
 taste pore leads to the taste pit
taste pore
⇓

46. Taste bud morphology
taste pore
⇓
photomicrograph
⇓
electron micrograph
⇒

47. Taste bud cells
 supporting cells
 neuroepithelial cells
 basal cells (stem cells)

48. Taste bud neuroepithelial cells are chemoreceptors
 Apical cell surface possesses microvilli
 pass through the taste pore
 are bathed by saliva
 contain membrane chemoreceptors for taste molecules
microenvironment - saliva
⇓

49. Taste bud innervation
 Neuroepithelial cell basal portion synapses with
afferent and efferent nerve fibres
⇒
• chorda tympani of n. facialis (VII)
⇐
• n. glossopharyngeus (IX)
⇐
• from taste buds of the epiglotis
n. loryngeus superior of n. vagus (X)

50. Sensory neurons of the taste analyzer
 are in sensory ganglia associated
with the cranial nerves:
• n. facialis
• n. glossopharyngeus
• n. vagus

51. Taste bud neuroepithelial cell differentiation
 Perception of the taste sensations
bitter ⇒
sour (acid) ⇒
salt ⇒
sweet ⇒

52. Thank you for attention!