Jittipan Chavadej,Ph.D.
Microanatomy
for
Medical students
Nov. ,43
Dept. of Anatomy, Fac. of Science
Mahidol University
Transverse section of the eye
Structure of the eye
Hollow, spherical structure
dia.~2.5 cm
3 distinct layers
-outer fibrous tunic (corneoscleral coat)
-middle vascular tunic (choroid)
-inner nervous tunic (retina)
Sclera
-thick, fibrous layer~ 0.6-1mm thickness
collagen,elastic & fibroblasts(betw.
fiber bundles)
Tenon’s capsule-thin sheet of CNT
separating eyeball from adipoes tissue
Episcleral space-betw
sclera&Tenon’s capsule--> rotation of
eyeball
Cornea
Corneal epithelium
~5 layers of unkeratinized cells,
rich insensory nerve ending,
regeneration
Bowman’s membrane
-lamina 10-12um thick
-thin collagen fibrils(random)
Stroma (substantia propria)
-90% of the thickness of cornea
-lamellae of collagen fiber(200-250)
-fibroblast&fiber-chondroitin
sulphate and keratan sulphate
Endothelium
-simple squamous epi.
-inner surface of cornea
-numerous pinocytotic vesicles
-Na+ pump-> Na+ into antr
chamber =resorption of excess
fluid->dehydration of stroma
Descemet’s membrane
-thick basement membrane-underlying endothelium
-thin at birth-->older-thicker (thin collagen fibrils)
Sclerocorneal junction(limbus)
-transition betw sclera & cornea
-inner surface-trabecular meshwork
strands of CNT
(covered by endothelium)
-->Schlemn’s canal (tubular space -> deep
vein of the limbus -> epicleral vein)
-drainage pathway of aqueous humor
Clinical correlation
Glaucoma
-failure of drainage of
aq. humor --> increased
intraocular pressure
-lead to progressive
damage to the eye,
retina --> blindness
(untreated)
Drawing of sclerocorneal junction,iris, lens, and ciliary body as
seen in meridian section
Middle layer: Tunica vasculosa
-is composed of 3 parts
1. Choroid
2. Ciliary body
3. Iris
Choroid
-thin, highly vascular layer
-contain many blood vv - loose CNT
-black color-presence of melanocytes
-inner surface-choriocapillary layer
for providing nutrient to retina
-Bruch’s mem.-refractile layer
-antrend-ora serrata(dentated ant
r
margin of retina)
Ciliary body
thickening of
vascular tunic
epith.-2layers+
loose CNT
Epithelium- 2layers
-outer=unpigmented
-inner=pigmented
Unpigmented epith.:mitochondria, RER etc
Zonule fibers-fibrillin :--> lens for anchoring lens in place
Ciliary processes: 70 processes radiate out from the
central core (fenestrated-capillaries)
folding of plasma mem.-transporting H2O,ions-aq. humor
SEM micrograph of postr surface of the lens.
note:lens, suspensory ligament, ciliary body
Ciliary muscle
2 bundles of sm. muscle
-is inserted into sclera
-is inserted along the inner
wall of ciliary body
*Contraction-release
tension --> lens : more
convex
Relaxation of ciliary muscle
Contraction of ciliary muscle
Iris:antr extension of
choroid --> pupi
-stroma: CNT+melanocyte
-antr surface:incomplete
layer
-postr surface:2layers of
epith.
*Dilator pupillae muscle
*Sphinctor pupillae muscle
Refractive media of the
eye :
cornea
lens
vitreous body
Vitreous body
-transparent refractile gel
-adhere to the retina over
the entire surface
99%=H2O+electrolyte+collag
en fibers+hyaluronic acid
Lens
-flexible, biconvex
-consist of 3 parts
-lens capsule
-subcapsular epithelium
(antr surface of the lens)
-lens fibers-2000 fibers
7-10mm long -mature
EM micrograph
of lens fibers
crystallins, few organelles
Macula lutea
-2.5mm lateral to the optic
disk
-1.5mm in diameter
-fovea centralis: 500um
*greatest visual acuity
*only cones are present
Blind spot:optic disk
=exit site of the optic
nerve
Optic disk(optic papilla) small round area -devoid of
photoreceptor cells
Retina seen through the
pupil showing optic disk
and macula lutea(yellow
spot) & fovea centralis
Retina
1
4
note:
sclera,choroid
retina
6
8
10 distinct layers
1.pigment epithium
2.layer of rods & cones
3.outer limiting mem.
4.outer nuclear layer
5.outer plexiform layer
6.inner nuclear layer
7.inner plexiform layer
8.ganglion cell layer
9.optic nerve fiber layer
10.inner limiting mem.
Pigmented epithelium
Outer nuclear layer
-nuclei of rods & cones
Inner nuclear layer
-nuclei of bipolar neurons amaccrine,horizontal,
Muller cells
Ganglion cell layer
-multipolar neurons
2-3Rods
2-3bipolar neurons
1ganglion cell->Single nerve fiber
1 Cone
1 bipolar neuron
1 ganglion cell
Rod:activated in dim light
Outer segment
 several hundred flattened
membranous lamellae(invagination
of plasma mem.-->detached from cell
surface)
membrane contain rhodopsin
(a light-sensitive pigment)
Inner segment
mitochondria-glycogen
granules RER,SER,golgi cpx.
proteins-->outer seg.->disk
Cone :activated in bright light
Lamellae-attached to plasma
membrane
are sensitive to color
Diagram of the
morphology of a rod
and cone
note:outer&inner seg.,
connecting stalk,
synaptic region
EM micrograph of portion of
outer & inner segment of cone
EM micrograph of portion of
outer & inner segment of rod
Note:ellipsoid-shape
mitochondria
Pigment Epithelium
-cuboid to columnar cells
-mitochondria-cell invagination
-*desmosome-zonulae occludentes-zonulae
adherentes--> lateral cell mem.-forming
blood-retina barrier
-apical surface->microvilli & sleeve-like
structure-surround the tip of rod & cone
cells (detached retina-hard jolt)
Pigment epithelium(cont.)
-abundance of melanin granules
-function:
absorb light after it has passed through
and stimulated the photoreceptor cells->preventing reflections from the tunic
phagocytized spent membranous disks
from the tip of the rods
play an active role in vision by esterifying
vit.A derivatives in their SER.
Eyelids
-skin
-loose CNT-muscles
-tarsal plate-dense CNT
Meibomian gland (modified
sebaceous gland)->thin
lipid layer
over tear film-retard its
evaporation
Lacrimal glands
-tubuloalveolar gland
-alveoli-serous columnar cells
-tear film -over the bulbar conjunctiva
and cornea
-tear--> lacrimal puncta-->lacrimal duct->lacrimal sac-->nasolacrimal duct-->infr
meatus of nasal cavity
Jittipan Chavadej, Ph.D.
Dept. of Anatomy,Fac. of Science,
Microanatomy for
Medical student
Dec.43
Mahidol University
Diagram showing major parts of the ear
3 regions :
 external ear,
 middle ear, and
 internal ear
External ear
Auricle: elatic cartilage plate-skin
External auditory meatus:skin lining
+cerumenous gland (modified sweat gland)
>tympanic membrane
--
Middle ear
Tympanic cav.:
Air-filled space
Ear ossicles
Tensor tympani
Stapedius
Eustachain tube
Tympanic membrane:
outer surface-thin layer of epidermis middle-tough layer of CNT
inner surface-sq. epith. that line tymp.
cavity
Tympanic cavity communicates :
-antr-->nasopharynx-Eustachain tube
-postr --> mastoid air cells
-oval&round windows-medl wall,
-connect to inner ear
Ear ossicle chain :
-tympanic membrane - malleus--incus->stapes - oval window
Middle ear -2 small muscles
tensor tympani-medl surface of
malleus & cartilagenous wall of auditory
tube-->pull malleus inward
stapedius-postr surface of
stapes&inner wall of tympanic cav.-->pull
stapes outward
Loud sound-->contraction of mus.->movement
of malleus & stapes
bridge of ear ossicles-more rigid->vibration
to inner ear is reduced
Auditory tube
 Connect the middle ear to the
throat
 Helps to maintain equal air pressure
on both sides of the ear drum
 Usually closed-open by swallowing,
yawning-->hasten the equalization of air
pressure during altitude changes
Provide the route for middle ear
infection
Inner ear
A
Osseous labyrinth bony canal
memb. labyrinth B
tube lies within the bony
canal
A=bony labyrinth
C
B=bony cochlea-mem. part
C=membranous labyrinth
 Inner Ear
 Vestibule - Utricle and saccule
 Semicircular canals Semicircular ducts
 Cochlea - Cochlear duct
Perilymphatic space-betw. bony &
memb. parts - perilymph
perilymph-is secreted by the
cells in the wall of the bony canal
All portions of membranous
labyrinth contain a fluid = endolymph
Vestibule - saccule & utricle
Wall-thin outer vascular leyer of CNT
-inner layer of simple squamous-low
cuboidal epithelium
specialized region=receptors
saccule-macula sacculi -floor
utricle-macula utriculi -lateral wall
M. utriculi/
sacculi
Hair cells
otolithic
membrane
otolith
Type I Hair Cell
•Round base,narrow neck
•RER,Golgi cpx,numerous small
vesicles
•Single kinocilium
•Stereocilia-dense terminal
web(actin filaments cross-linked by
fimbrin) bending at the neck region
•surrounded by a cup-shaped
afferent nerve fiber
Type II Hair Cell
Similar to type I hair cell
longer,more columnar in shape
many small nerve endings
synaptic ribbons-function in
synapses with efferent nerves
for modulaing sensitivity
Supporting cell-interposed betw. Type I&II hair cells
A
B
SEM micrograph of the bundle of stereocilia on the
vestibular hair cell
A-hair cell of bull frog
b-hair cell found in utricle & saccule
Supporting cell
A few microvilli-apical surface
a well-developed Golgi cpx.+ secretory
granules
thick junctional cpx. to the hair cells
fn.:-help to maintain hair cell ?
-may contribute to the production
of endolymph ?(dark cell of non receptor
region)
Otolithic membrane :
thick gelatinous glycoprotein mass
otolith (otoconia)-on the surface
region of otolithic membrane
otolith=small calcium carbonate
crystals
Bending the head
- cause displacement
of endolymph->otolith->bending of
stereocilia->action
pot.->nerve impulse>brain-inform the
position of the head
Semicircular ducts
3 ducts-perpendicular to each other
lined by cuboid epithelium
contain endolymph
each has a small dilatation=ampulla
transverse ridge(floor of ampulla)=crista
ampullaris-receptor region
Crista ampullaris:
hair cell+supporting cells(stereocilia & single
kinocilium)
cupula-conical,gelatinous structure->lumen of
ampulla
Head-stationary
position
Crista amp.-upright
Head moving
Cupula-bending
Angular acceleration of the head->movement of
endolymph->stereocilia->electricle impulse->brain
3 chambers: S. vestibuli,S. media,S.tympani
S.vestibuli&S.tympani - helicotrema(apex of cochlea)
S.media end at the tip of the spiral
S.media-specialized receptor organ=organ of Corti
 Cochlea
35mm in length
23/4 turns around modiolus
-spiral ganglion-->organ of Corti
S. vestibuli
S. media
Vestibular mem.
(sponge bone)
S. tympani
Basilar mem.
Lateral wall:thicken stratified
epith.=stria vascularis
Cells at supllayer-microvilli+
basal infolding-->maintenance
H2O&electrolyte composition
Organ of Corti
•Hair cells+several types
of supporting cells
•Tectorial membrane
•Basilar membrane
2 types of hair cell:
Micrograph of organ of
Corti sitting on basilar
membrane (cross section of
cochlea)
•inner hair cell
•outer hair cell
Tectorial membrane:
•proteoglycan-rich gelatinous mass
•containing fine keratin-like filaments
Hair cells of organ of Corti
Do not have a kinocilium, but a basal
body is present
Inner hair cell(hair cell type I):
mito., RER, SER, small vesicles
50 - 60 stereocilia arranged in a V
shape
Outer hair cell
(hair cell type II):
elongated cylindrical cell
abundant RER, mito-basal
portion
100 stereocilia arranged in a W
shape
SEM micrograph of
guinea pig organ of
Corti seen from above.
Note: The W-shape of the bundles of stereocilia on the outer
hair cells is less clear than in the human.
Cochlear function
Sound wave-->ext. auditory meatus
-->movement of tympanic mem.-->
vibration of ear ossicles-->oval window
(foot of stapes)-->pressure
wave in
perilymph -S.ves.->S.tymp.-->vibration of
basilar mem.--> Hair cells of organ of
Corti-generate impulse-->Brain
Effect of sound waves on cochlear structures
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