The ear consists of the external, middle, and inner ear. The inner ear contains the cochlea which houses the organ of Corti for hearing and the vestibular organs like the saccule and utricle for balance. Sound waves are transmitted through the external ear to the middle ear bones and then vibrations reach the inner ear where they are transduced by hair cells into nerve impulses for hearing and balance.

1. SPECIAL SENSES - EARS
2015 -Section A Laboratory Trans

2. HANDOG NG
A. B. C.

3. Anj Barbin Claresse

4. EAR
Consists of 3 parts:
1. EXTERNAL EAR – receives sound waves
2. MIDDLE EAR – sound waves are transmitted from
air to bone & by bone to internal ear
3. INTERNAL EAR – vibrations are transduced to
specifc nerve impulses that pass via acoustic nerve
to CNS; also contains vestibular organs which
maintains equilibrium

5. Objectives
1. Describe the histology of • Describe the otolith.
external, middle, and inner • Identify the ff. in a section of
ear & tympanic membrane the cochlea under LM:
2. Describe the histology of – Spiral lamina
the ff.: – Scala vestibulii
1. Macula of the saccule/utricle – Vestibular membrane
2. Crista ampullaris – Cochlear duct
3. Organ of Corti – Tectorial membrane
4. Vestibular membrane – Basilar membrane
3. Trace conjunction of sound – Scala tympani
vibrations from the – Organ of Corti
tympanic membrane to the – Mociolis
organ of Corti. – Cochlear nerve
– Spiral ganglion

6. PARTS OF THE EAR
A, Auricle
B, External auditory
meatus
C, Tympanic
membrane
D, Semicircular canals
E, Vestibule
F, Cochlea

7. EXTERNAL EAR
• Skin of the auricle = keratinized stratified
squamous epithelium (not shown)
• Dermis
– with small hair follicles
– DCT continuous w/ perichondrium that surrounds
elastic cartilage (located in the center of the
structure)
– Elastic cartilage imparts flexibility to the auricle

8. HAIR FOLLICLE
DCT
ELASTIC
CARTILAGE

9. External Auditory Meatus
• The skin lining the external auditory meatus (canal) is generally thin
but contains hair follicles and large ceruminous glands that extend
through the dermis to reach the perichondrium of the cartilagenous
part of the tube.
• Hairs - aid in preventing intrusion of insects into the ear canal
• Ceruminous gland
– has a large lumen
– either cuboidal (inactive) or columnar (active) epithelium
– closely resembles axillary apocrine sweat glands.
– coiled tubular apocrine sweat gland
• Cerumen
– waxy secretion of the ceruminous glands may protect the skin from
desiccation and irritation
– yellowish, semisolid mixture of wax and fats

10. External Ear
(ceruminous
gland)

11. External Auditory Meatus
F – Hair Follicles
G – Ceruminous
Gland

12. Tympanic Membrane (Eardrum)
• Oval membrane; epithelial sheet
• External surface is covered with a thin layer of
epidermis
• Inner surface is covered with simple cuboidal
epithelium continuous with the lining of the tympanic
cavity
• Between the 2 epithelial coverings is a tough
connective tissue layer composed of collagen, elastic
fibers, & fibroblasts
• Fxn: Vibrations of the tympanic membrane produced
by sound waves transmit sound wave energy to the
middle and inner ear

13. MIDDLE EAR
• Contents:
– Tympanic Cavity/ Tympanic Membrane
– Oval Window
– Round Window
– Ossicles
• Malleus
• Incus
• Stapes

14. Tympanic cavity
• Air-filled
• Irregular space that lies within the temporal bone between the
tympanic membrane and the bony surface of the internal ear
• Communications:
– Anterior: communicates with the pharynx via the auditory tube
(Eustachian tube)
– Posterior: smaller, air-filled mastoid cavities of the temporal bone.
• Lined mainly with SIMPLE CUBOIDAL EPITHELIUM resting on a thin
lamina propria that is strongly adherent to periosteum.
• Near the auditory tube, this simple epithelium is gradually replaced
by the CILIATED PSEUDOSTRATIFIED COLUMNAR EPITHELIUM
lining the tube.

15. Auditory ossicles
• Series of small bones that connects tympanic
membrane to the oval window
• transmit the mechanical vibrations of the
tympanic membrane to the internal ear
• covered with SIMPLE SQUAMOUS EPITHELIUM
• Three ossicular bones:
1. MALLEUS – “hammer”; attached to connective tissue
of the tympanic membrane
2. INCUS – “Anvil”
3. STAPES – “Stirrup”;attached to connective tissue that
of the membrane in the oval window

16. Tympanic Membrane
& Ossicles
3 Layers of Tympanic Membrane
C – cuticle layer (external)
- consist thin layer of skin
Fi – fibrous layer
- type I & Type II collagen
M – mucus layer (internal)
- cuboidal cells
Ossicles
CB – Compact Bone
Ca - Cartilage
Mu – Tensor Tympani Muscle

17. INTERNAL EAR
• Bony Labyrinth
• Membranous Labyrinth

18. Summary:
Bony Membranous Receptor
Functions
Labyrinth Labyrinth Organs
Vestibule Saccule & Macula Equilibrium
Utricle (Linear
acceleration)
Semicircular Semicircular Crista Equilibrium
Canal Duct Ampullaris (Angular
acceleration)
Cochlea Cochlea Organ of Corti Hearing

19. Middle & Inner Ear

20. Bony Labyrinth
• lined with endosteum
• separated from the membranous labyrinth by the
perilymphatic space
– This space is filled with a clear fluid called the
perilymph, within which the membranous labyrinth is
suspended.
Three components:
1. Semicircular canal
2. Vestibule
3. Cochlea

21. Bony Labyrinth
• Semicircular Canals (SC) • Cochlea
– Sup, pos, lateral – Hollow, bony spiral that
– One end of each canal is turns around itself like a
enlarged (ampulla) snail around central bony
– Enclose semicircular ducts column (Modiolus)
– Contains cochlear duct
• Vestibule
– Central region bet SC &
cochlea
– Houses saccule & utricle
– also contains oval (where
stapes is related) and
round window

22. B – Bone
SC – Semicircular Canals
Arrow - Fibroblast

23. COCHLEA OF THE INNER EAR
A. Anatomy of bony labyrinth
B. Anatomy of the membranous labyrinth
C. Sensory labyrinth.

24. Membranous Labyrinth
• epithelium derived from the embryonic
ectoderm which invades the developing
temporal bone
• Contains circulating endolymph
Specialized Areas:
– Saccule & Utricle
– Semicircular ducts
– Cochlear duct

25. ML - Membranous
Labyrinth
(Lined by SQUAMOUS
EPITHELIUM)

26. SACCULE & UTRICLE
• thin sheath of connective
tissue lined with simple
squamous epithelium
• Consist of MACULA
– neuroepithelial cells
innervated by vestibular
nerve
– receptors for sensing
orientation of the head
relative to gravity (saccule) &
acceleration (utricle)
– Consist of the ff cells:
• Receptor Hair Cells
• Supporting Cells
• Aff & eff nerve endings

27. Macula of the saccule -ilocated in the
wall, thus detecting linear vertical
acceleration
Macula of the utricle
located in the floor, thus detecting
linear horizontal acceleration).

28. Macula of the Saccule & Utricle
Consist of two types of cells:
• Supporting cells
– Columnar; with nuclei nearest the
basement membrane
• Sensory receptor (or hair) cell
2 Types of Hair cells:
a) Type I hair cells (flask shaped)
b) Type II hair cells (cylindrical)
• Both have nerve terminals &
stereocilia
• Also possess OTOLITHIC MEMBRANE
– gelatinous membrane of
glycosaminoglycans that contains
crystals of calcium carbonate &
protein (OTOLITHIS)
It is difficult to resolve the two types of hair cells in light micrographs. In this image, the more
rounded cells are most likely type I hair cells.

29. Macula of
the Utricle

31. Arrow – otoliths
Arrow head - stereocilia

32. Hair Cells
• Type I hair cells
– GOBLET cells
– bulbous in shape and stain
poorly
– nuclei tending to lie at a
lower level than type II
– invested by a meshwork of
dendritic processes of
afferent sensory neurones
• Type II hair cells
– COLUMNAR CELLS
– more slender in shape
– have only small dendritic
processes at their bases
SUPPORTING CELLS

33. SEMICIRCULAR DUCT
• Arise/ continuation of utricle
• Ampullae – expanded regions at its lateral ends
• Receptor Organ: CRISTAE AMPULLARES
• Composed of
– Supporting cells
• sit on the basal lamina
– Hair cells
• type I and type II hair cells, exhibit the same morphology as the
hair cells of the maculae
– Cupula
• a gelatinous glycoprotein mass overlying the cristae ampulares
• similar to the otolithic membrane in structure and function
• cone-shaped and does not contain otoliths

34. Semicircular Ducts (Crista Ampullaris)

36. Crista
Ampularis
Black & Green Arrow – Cupula
Red - Type I Hair cell
Yellow - Supporting cells

37. COCHLEAR DUCT
• a diverticulum of the saccule
• highly specialized as a sound receptor
• surrounded by perilymphatic spaces
• appears to be divided into three spaces:
– SCALA VESTIBULI (above)
• Contains PERILYMPH
– SCALA MEDIA (cochlear duct) in the middle
• Contains ENDOLYMPH
• Roof: vestibular (Reissner’s) membrane
• Floor: basilar membrane
– SCALA TYMPANI
• Contains PERILYMPH
The SV & ST are continuous (from oval window to round window) & communicate at the
apex of the cochlea via an opening known as the helicotrema.

39. Inner Ear: COCHLEA (vertical section)

41. COCHLEA
O – Organ of Corti
SV – Scala Vestibuli
SM – Scala Media
ST – Scala Tympani

45. COCHLEAR DUCT (Scala Media) Parts
1. Vestibular (Reissner's) 3. Stria Vascularis
Membrane – pseudostratified epithelium
– consists of 2 layers of – contains intraepithelial plexus of
squamous capillaries
epithelium, derived from – Covers lateral wall of cochlear duct, b/w
scala media & scala vestibular membrane & spiral
vestibuli prominence
– preserve very high ionic – responsible for ionic comp of
gradients across endolymph
membrane
4. Spiral prominence
2. Basilar Membrane – in inferior portion of lateral wall of
– supports the organ of Corti cochlear duct
– composed of two zones: – small protuberance that juts out from
• Zona arcuata - thinner, lies the periosteum of cochlea into cochlear
more medial duct
• Zona pectinata - similar to
a fibrous meshwork – Continious with stria vascularis cells
containing a few fibroblasts • These cells are reflected into the spiral
sulcus, where they become cuboidal
• Cells of this layer continue onto the basilar
lamina as the cells of Claudius, which
overlie the smaller cells of Böttcher

47. COCHLEAR DUCT (Scala Media)

48. COCHLEAR DUCT & ORGAN of CORTI

49. A, Scala vestibuli B, Scala tympani C, Scala media (cochlear duct) D, Tectorial membrane
Arrowhead – Vestibular membrane Arrow – Basilar membrane Curved Arrow – Stria vascularis
Double arrowhead – Spiral prominence

50. COCHLEAR DUCT Parts
5. Limbus of the Spiral Lamina 6. Tectorial membrane
– Locates at the narrowest – proteoglycan-rich
portion of the cochlear gelatinous mass
duct, where vestibular & – contains numerous fine
basilar membranes meet keratin-like filaments
– Formed from the bulging out – overlies organ of Corti
of the periosteum (into the – where the stereocilia of
scala media) covering the hair cells of the organ of
spiral lamina Corti are embedded
– Part of the limbus projects over – Secreted by interdental
the internal spiral sulcus cells (found in the body of
(tunnel). spiral limbus)

51. ORGAN OF CORTI
• receptor organ for hearing
• lies on the basilar membrane
• composed of hair cells and supporting cells.

52. O osseous spiral lamina SL spiral limbus SLig spiral ligament SM scala media
T tunnel of Corti TM tectorial membrane Svasc Stria Vascularis

53. Organ of Corti – Supporting Cells
INNER AND OUTER PILLAR CELLS (IP & OP) INNER PHALANGEAL CELLS
– tall cells with wide bases and apical end – located deep to the inner pillar cells
– shaped like an elongated "I" – completely surround the inner hair cells they
– attached to the basilar membrane, and support
each one arises from a broad base
– support the hair cells of the organ of Corti BORDER CELLS
Inner tunel – delineate the inner border of the organ of
– Medial wall formed by IP Corti
– Lateral wall: OP – slender cells that support the inner aspects of
IP >OP (usu 3 IP vs 2 OP. the organ of Corti
OUTER PHALANGEAL CELLS CELLS OF HENSEN
– tall columnar cells attached to the basilar – define the outer border of the organ of Corti
membrane – tall cells
– With cup-shaped apex – b/w outer phalangeal cells & shorter cells of
– support the basilar portions of outer hair Claudius, which rest on the underlying cells of
cells along with bundles of eff & aff nerve Böttcher.
fibers (which pass between them on their
way to the hair cells)
– Found below the hair cells
Space of Nuel - fluid-filled gap around unsupported
regions of the outer hair cells that conects with
inner tunnel

54. Organ of Corti - Hair Cells
specialized for transducing impulses for the organ of hearing
Has TWO TYPES (depending on location)
Inner hair cells Outer hair cells
– single row of cells supported – supported by outer
by inner phalangeal cells phalangeal cells
– extend the inner limit of the – near the outer limit of the
entire length of organ of Corti organ of Corti
– Short – elongated cylindrical cells
– centrally located nucleus – nuclei are located near their
– w/ stereocilia ( "V" shape) bases
– No kinocilium – W/ stereocilia ("W”-shaped )
– basal aspects of these cells – synapse with afferent and
synapse with afferent efferent fibers on its base
cochlear nerve – Nokinocilium
– arranged in rows of three (or
four) along the entire length
of this organ

57. orh

58. Arrowhead (left) – Inner Pillar cell Arrowhead (right) – Outer Pillar cell
Arrow - Outer Phalangeal cells Blue arrow – Tectorial membrane
Red Arrow – Inner Hair cell Yellow Arrow – Outer Hair cell
Curved Arrow – Hensen’s cell Diamond (green) – Inner Tunnel

59. Description of Image
• The organ of Corti contains a single row of inner hair cells (arrow) nestled in
cytoplasmic recesses of the inner phalangeal cells. Thus, the inner hair cells do not
touch the basilar membrane.
• The inner hair cells have a rounded base and a short neck, similar in appearance to
the type I hair cells of the cristae and maculae. Their apical surface has 50 to 70
stereocilia.
• In addition to the phalangeal cells, the inner hair cells are held close to the
tectorial membrane by cytoplasmic extensions from the inner pillar cells
(arrowhead). These cell processes contain aggregations of microtubules.
• There are three to five rows of outer hair cells (curved arrow) and one row of inner
hair cells in the organ of Corti. The outer hair cells are cylindrical in shape, similar
to the type II hair cells of the cristae and maculae.
• The outer hair cells do not rest directly on the basilar membrane; they are cradled
by the outer phalangeal cells (arrow). Recall that the inner hair cells are also
supported by the inner phalangeal cells. Thus, each row of hair cells has a
corresponding row of phalangeal cells.
• Fingerlike extensions of the phalangeal cytoplasm abut the apical cytoplasm of the
hair cells to keep these cells close to the tectorial membrane. These cytoplasmic
areas of the phalangeal cells contain bundles of microtubules. The phalangeal cells
and the inner and outer pillar cells (arrowheads) provide the major structural
support for the hair cells.

60. Tips
• Pag nasa side ng Tectorial
membrane, “INNER” un (meaning inner cell or
if sa baba nun inner phalangeal cell)
• Mas marami ang rows ng Outer hair cell kesa
sa Inner hair cell.
• For the pillar cells, nasa paligid lang siya ng
inner tunnel. Again, pag nasa side ng tectorial
membrane inner pillar (usu mas marami din)

61. Spiral Ganglion

62. Spiral ganglion