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
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
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
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
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
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.
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
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.
41. COCHLEA
O – Organ of Corti
SV – Scala Vestibuli
SM – Scala Media
ST – Scala Tympani
42.
43.
44.
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
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
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)
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.The hairs may aid in preventing intrusion of insects into the ear canal, and the waxy secretion of the ceruminous glands may protect the skin from desiccation and irritation.The coiled ceruminous gland has a large lumen, and the cells are either cuboidal (inactive) or columnar (active). The gland closely resembles axillaryapocrine sweat glands. The secretory product, cerumen (ear wax), is a yellowish, semisolid mixture of wax and fats. These glands are considered a special variety of coiled tubular apocrine sweat gland.
Within the cavities of the petrous portion of the temporal bone (B) are fluid-filled channels in the inner ear, suspended from the bone by delicate collagenous fibrils. The innermost of these structures is the membranous labyrinth, one of which is part of the semicircular canals (SC). The membranous labyrinth is filled with a fluid called endolymph, which has a composition similar to intracellular fluid, having a relatively high potassium content. For most of its length, the membranous labyrinth is lined with simple squamous epithelium, with the exception of six regions of neurosensory epithelium.Fibroblasts (arrow) and collagen fibrils are found within the region between the bony and membranous labyrinths. The fluid found in this middle region is called perilymph and is similar in composition to extracellular fluid, in that it has a relatively high content of sodium ions; thus, it is different in ionic composition from endolymph.