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LECTURE NOTE
MODULE OF SPECIAL SENSE
AN OVERVIEW IN THE HISTOLOGICAL ASPECT
Ahmad Aulia Jusuf, MD, PhD
Departement of Histology
Faculty of Medicine University of Indonesia
Jl. Salemba Raya 6 Jakarta
2009
Introduction
The special senses are also known as the sensory endings or receptors. They are the
terminal of dendrites which perceive the various sensory stimuli and transmit these inputs to the
central nervous system. According to the source of stimuli, these sensory receptors can be
grouped into 3 groups:
1. Exteroreceptor
Exteroreceptor are receptors that perceive the stimuli from the external environments.
They locate near to the body surface. This group is classified into 3 subgroups
a. Exteroreceptor which is a component of general somatic afferent. This
receptor is sensitive to temperature, touch, pressure and pain
b. Exteroreceptor which is a component of special somatic afferent. This
receptor is specialized for perceiving light (sense of vision) and sound (sense
of hearing)
c. Exteroreceptor which is a component of special visceral afferent pathways.
This receptor is specialized to smell and taste.
2. Proprioreceptors
Proprioreceptors are specialized receptors, components of general somatic afferent and
are located in joint capsule, tendons and intrafusal fibers within muscle. These
receptors transmit sensory inputs to the central nervous which is translated into
information that related to the awareness of body in space and in movement. Receptor
vestibular which is located in the inner ear receives the stimuli related to motions
vectors within the head. In the central nervous system the inputs are processing into
the awareness of motion for corrective balance.
3. Interoreceptor
Interoreceptors are specialized receptors, a component of general visceral afferent that
perceives the information from within organs of the body.
In this module we will focus on eye as the sense receptor of light and ear as the sense receptor of
hearing.
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EYES
Eye (Fig-1) is photosensory organ of
Figure-1 The Eye
body that perceive the light stimuli. The
light passes through the cornea, lens and
several refractory structures within the
orb. Light then is focused by lens on a
light sensitive portion of the neural tunic
of the eye, known as retina. Retina
contains the photosensitive, rods and
cones that change the light inputs into the
visul information. The visual information
then is transmitted by the optic nerve to
the brain for processing.
The bulb of eye is composed of
Fig-2 The histological picture of the wall of eye ball
three tunics (coats)
1. Fibrous
layer)
tunic
which
(sclero-cornea
performs
the
outermost coat of the eye. This
part consists of sclera and cornea.
This part also receives insetions
of the extrinsic muscles of the
eye which are responsible for
coordinated movement of the eye
to gain the various visual fields.
2. Vascular tunic (uvea layer /
tunica vasculosa) which performs
the middle coat of the eye. This
part consists of choroids, ciliary
body and the iris.
3. Neural tunic which performs the innermost coat of the eye. This part consists of retina.
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A. FIBROUS TUNIC (SCLERO-CORNEAL LAYER) (Fig-1 dan 2)
The fibrous tunic performs a fibroelastic capsule that strongly keeps the shape of eye ball.
This tunic is divided into two parts, the sclera and cornea. Sclera is the white part of the eye ball
that performs 5/6 part of the eye ball. Cornea is a black part of eye that performs 1/6 part of eye
ball. The junction area between cornea and sclera is called as limbus.
SCLERA
Sclera (Gk. Sclera=hard) is the white part of eye ball which is nearly devoid of blood
vessels (Fig-1and 2). It is composed by the type-1 of collagen fibers that is interlaced with the
network of elastic fibers. This arrangement gives form to the orb which is maintained by
intraocular pressure from the aqueous humor in the anterior part and vitreous body in the
posterior part. The sclera is perforated by the fibers of optic nerve in the posterior part at the
lamina cribosa (Fig-2). Sclera contains the blood vessels especially at the junction between
cornea and sclera, known as limbus.
CORNEA (Fig-3)
Figure-3 Cornea
Cornea is a transparent, avascular and highly innervated structure. This part is origin
from the bulging of fibrous tunic to the anterior part of eye ball. Cornea receives the nutrient by
diffusion manner from the peripheral blood vessels located in the limbus and from the aqueous
humor. Histologically cornea is divided into 5 layers:
1. Corneal epithelium
It is a continuation of conjunctiva, consists of stratified squamous non keratinized
epithelium composed of five to seven layer. The corneal epithelium is highly innervated
by numerous free nerve endings. The superficial cells in corneal epithelium are rapidly
turn overed by the underlying cells. The corneal epithelium also functions in transferring
water and ions from the stroma into the conjunctival sac.
2. Bowman’s membrane.
Bowman’s membrane is a fibrous layer which lies immediately deep to the corneal
epithelium. It is composed by type I collagen fibers.
3. stroma
Stroma is the thicknest layer of cornea which is composed of collagen connective tissue
mostly of type 1 collagen fibers. These fibers are arranged in the parallel manner each
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other to make a lamel liked structure. The fibroblasts are located between the collagen
fibers.
4. Descement’s membrane
Descement membrane is a thick basement membrane, composed by collagen fibers.
5. Corneal endothelium
The corneal endotheliu is the innermost layer of cornea, formed by a simple squamous
epithelial cell. The corneal endothelium synthesizes the protein that is necessary for
maintaining the descement’s membrane. The cells have many pinocytic vesicles, and
their membranes have sodium pumps that transports the excessive sodium ion into the
anterior oculi chamber. These ions are passively followed by chloride ions and water.
The excess water within stroma will be reabsorbed by endothelium to keep the stroma
relatively dehydrated, a factor that contributes to maintaining the refractive quality of the
cornea.
LIMBUS (SCLEROCORNEAL JUNCTION)
Limbus (sclerocorneal junction) (Fig-4) is the boundary of cornea and sclera. On its outer
aspect there is an outer depression of stroma called as external sclera sulcus, where the gently
curving sclera is continuos with the more convex cornea. On its inner aspect, there is also
depression called as internal scleral sulcus, which is filled by the trabecular meshwork with its
trabecular space, also known as Fontana space and canal Schlemm. On the posterior lip of the
internal scleral sulcus, the scleral stroma projects toward the interior of the eye forming a small
circular ridge called as scleral spur. Limbus is covered by a transition of the corneal epithelium
into the epithelium of conjunctiva of the bulb. The epithelium of bulb conjunctiva is composed by
the simple columnar epithelial cells with its underlying lamina propria. The stroma of limbus is
performed by the unification between sclera and cornea. This stroma consists of fibrous connective
tissue.
Figure-4 Sclerocorneal junction (Left) and canal of Schlemm (Right)
CANAL OF SCHLEMM
The canal of Schlemm, a flattened vessel extends around the entire circumference of the
limbus just anterior to the scleral spur. The lumen is lined by simple squamous epithelial cell.
This canal will continue to the scleral plexus and finally drainages to the plexus of scleral vein.
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B. TUNICA VASCULOSA / UVEA (L. Uva= grape) (Fig-2 and 5)
Figure-5 Tunica vasculosa
The vascular middle tunic of the eye, the tunica
vasculosa (uvea) consists of three parts: the choroids,
the ciliary body and the iris (Fig-2 and 5)
CHOROID (Fig-5 and 6)
The choroid is the richly vascularized pigmented
layer of the posterior wall of the orb that is loosely
Figure-6 Choroid
attached to the tunica fibrosa. Choroid consist of
many blood vessels and pigment cells that give the appearance of this part to be brown in color
This layer is composed of collagen and elastic fibers, fibroblast, blood vessels and melanocytes.
Choroid is divided into 3 layers (Fig-6):
1. Bruch’s membrane
Bruch’s membrane is the innermost component of the choroid consists of a network of
collagen and elastic fibers and basal lamina. This part is attached to the pigment
epithelium of retina
2. The choriocapillaries
This middle layer of choroid contains fenestrated capillaries that supply oxygen and
nutrients to the outer layers of the retina and fovea. The capillaries are responsible to
providing nutrient and oxygen to the outer part of retina
3. The choroidal stroma / vessel layer
The stroma consists of large arteries and veins surrounded by collagen and elastic fibers,
fibroblasts, a few smooth muscle cells, neurons of autonomic nervous system and
melanocytes
CILIARY BODY (Fig-7)
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Ciliary body is the wedge-shape extension of choroid that rings the inner wall of the eye at
the level of lens. It is located between ora serrata of retina and limbus. The ciliary body is
composed of loose connective tissue containing numerous elastic fibers, blood vessels and
melanocytes.
Figure-7 Ciliary body
The cilary body forms short, finger like projections, known as the ciliary processes. Fibers
composed of fibrilin radiate from the ciliary processes to insert into the lens capsule, known as
suspensory ligaments of the lens (zonula zinii) that anchores the lens in place.
The inner surface of ciliary body is lined by the pars ciliaris of the retina, a pigmented
layer of the retina, composed of two cell layers. The outer layer is composed of heavily pigmented
columnar epithelium, while the inner layer is composed by non pigmented columnar epithelim.
The cells in the inner layer secreted the low protein containing filtrated plasma known as humor
aqueous into the posterior oculi chamber.
After secreted by the ciliary body, humor aqueous is drainaged into the anterior oculi
chamber from posterior oculi chamber through the papillary aperture. From the anterior chamber
humor aqueous is drainage to canal of Schlemm through trabeculae space of Fontana. From canal
of Schlemm, humor aqueous is drainaged to plexus of scleral vein through scleral plexus.
The bulk of the ciliary body contains three bundles of smooth muscle cells called as the
ciliary muscle. One bundle stretches the choroids and opens the canal of Schlemm. Two other
bundles that attach to scleral spur reduce tension on the zonula zinii. As the result the lens
becomes thicker and more convex. This function is known as accommodation process.
In clinic, there is a condtion called as glaucoma, characterized by prolonged increasing of
intraocular pressure caused by the failure of drainage of humor aqueous from the anterior chamber
of the eye. If this condition is not treated it results in blindness
IRIS (L. Iris = rainbow) (Fig-4 and 8)
Iris is the outermost part of uvea layer, projecting from the ciliary body and forms a
diaphragma in the anterior lens. Iris separates the anterior chamber from the posterior chamber of
eye. The aperture between the right and left part of iris known as pupil (L pupil=little girl).
Iris is composed by loose connective tissue that contains the pigment and rich with the
blood vessels. The anterior surface of iris is irregular with the incomplete layer of pigmented cells
and fibroblasts. The posterior surface of iris is smooth and covered by continuation of the two
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layers of epithelium that cover the ciliary body. The surface toward to the lens contains many
pigment cells that protect the passing of light directly through iris. Thus the light will be focused
entering the eyes through pupils.
Iris contains two kinds of smooth muscle (Fig-8) the dilatator pupillae and sphincter
pupillae muscles. These two muscles control the diameter of pupil. The dilatator pupillae muscle,
innervated by sympathetic nervous system, dilates the pupil whereas the sphincter puplillae musle,
innervated by parasympathetic fibers of he oculomotor nerve (CN III) constricts the pupil.
Figure-8 Iris (CP = constrictor pupillae muscle, DP= dilatator pupillae muscle)
The abundant population of melanocytes located in the epithelium and stroma of iris influence
the colour of eyes. The eyes are dark when the number of melanocytes is large, whereas they are
blue when the melanocytes number is low
Lens (Fig-4 dan Gb-9)
Lens consists of three parts: lens capsule, subcapsular epithelium and lens fibers. The capsule
of lens is a basal lamina mostly composed by type IV collagen fibers and glycoprotein. This
capsule is elastic, transparent, and compaq structure. The subcapsular epithelium is located only in
the anterior surface of lens, immediately deep to the lens capsule. This epithelium is composed by
simple cuboidal cells. The bulk of lens is composed of long cells known as lens fibers. These cells
located immediately deep to the subcapsular epithelium and lens capsule. These cells have been
already loosed their nuclei and organelles. This lens fiber is filled by crystallins, the lens protein.
The present of crystalline will increase the refractory index of the lens.
Figure-9. Lens
Lens is completely free from the blood vessel. Its nutrient is received from the humor
aqueous and vitreus body. The lens is impermeable but it can be passed by the light easily. The
lens is hanging to the ciliary body by suspensory ligaments of the lens known as zonula zinii.
VITREOUS BODY (Fig-4 and 10)
Vitreous body is a transparent, refractile gel that fills the cavity of the eyes (vitreus
cavity), composed by mostly water (99%), electrolyte, collagen fibers and hyaluronate acids. In the
centrale of vitreus body there is a rudimenter canal knows as canal of hyaloidea. During the fetal
period this canal contains the arteri hyalodea. The vitreus body is necessary to maintain the shape
and elasticity of eye ball.
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Figure-10 Vitreus body
CHAMBERS OF EYES (Fig-4)
The eye contains two chambers, the anterior and posterior eye chambers. The anterior
chamber is a chamber which is lined in the anterior by the posterior part of cornea and by lens, iris
and the anterior surface of ciliary body. The lateral border of anterior chamber is the angle of iris
or limbus which is occupied by the trabeculae meshwork that play the role in drainaging the humor
aqueous to the canal of Schlemm. Posterior chamber is the chamber which is bordered by iris in
the anterior and the anterior surface of lens and zonula zinii in the posterior. The lateral of this
chamber is bordered by ciliary processus.
The anterior and posterior chamber is filled by humor aqueous. Humor aquous is a clear,
watery fluid secreted by the cilary epithelium and also produced by the diffusion process of the
plasma from capillaries in the ciliary processus. This solution contains the substance that can
diffuse from the blood plasma but with the low amount of protein.
Humor aqueous is secreted continuously to the posterior chamber then drainages to
anterior chamber through pupil. Humor aqueous then is drainaged to canal of Schlemm through
the trabeculae meshwork. In normal condition the secreted solution is balanced with the excreted
solution keeping the intraocular pressure to be constant at about 23 mmHg. The intraocular
pressure will be increased if there is an inhibition of passing humor aqueous, known as glaucoma.
If this condition is untreated the blndness will be occurred.
C. RETINA (NEURAL TUNIC) (Fig 5 and 11)
Retina, the innermost tunic of the eye, contains the
Figure-11 Optic Cup
photoreceptor cells, known as rods and cones. The
retina develops from the optic cup, an evagination of
the procencephalon which give rise to the primary optic
vesicle, whereas the stalk of the optic cup develops to
become the optic nerve. The outer wall of optic up
develops to be the outer pigment layer of retina
whereas the neural retina is origin from the optic cup.
The optic disk (Fig-12), located on the posterior of the
orb is the exit site of optic nerve. The nerve fibers in
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this area will be joined together to form a protrusion
called as papil of optic nerve. Because it does not
contain the photoreceptor cells, it is insensitive to the
light and is therefore called as blind spot of the retina.
The papil of optic nerve contains the arteries and venous centralis which give the nutrition to the
retina. The blockage of these arteries can cause the permanent blindness. Retina is also supplied by
other arteries such as the cilioretina arteri.
Optic nerve is not the peripheral neves but it is the tractus of nerve between the ganglion
retina and midbrain. The optic nerves contain more than one thousand mielinated nerve fibers and
pass through chiasma optic, supporting by neuroglia (astrosit). The meninges and subarachnoid
space exists from the brain as the sheath of optic nerve.
Figure-12. Optic disc (Left) and Fovea centralis (Right)
Approximately 2.5mm lateral to blind spot or optic disc is a yellow pigmented zone in the
retina wall called as the macula lutea (yellow spot) (Fig-12). In the center of macula lutea, at 4 mm
temporal to optic disc and 0.8 mm under the meridian horizontal, there is a depression area, called
as fovea centralis, where the visual activity is the greatest. Fovea centralis is specialized area of the
retina containg only cones, which are packed tightly as the other layers of retina are pushed aside.
The optic retina lines the choroid from the papil of optic nerve in posterior to the ora serrata in the
anterior. In the histological section (Fig-13 and 14) Retina consists of 10 layers, from outside to
inside:
1. Pigment epithelium
2. layers of cones and rods
3. outer limiting membrane
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 membrane
Pigment epithelium is a layer composed of cuboidal to columnar cells. The nuclei are cuboid,
whereas the cytoplasms are rich with the melanin pigment. The melanin pigment functions as
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1. Absorbing the light after it has passed through and stimulated the photoreceptors, thus
preventing reflections from the tunic.
2. giving the nutrition for photoreceptor
3. storage and releasing the vitamin A
4. synthesizes the rhodopsin
The rods and cones consists of two types cells of photoreceptor, the rod and cone cells
which are the modification of nerve cells. This layer contains the cytoplasm of rod and cone cells.
The rods are elongated specialized cells which composed of outer and inner segment, a
nuclear region and a synaptic region. The outer segmentsof rod cell is cylindric in shape with the
length of 28 micrometer and contains the photopigment of rhodopsin which are sensitive to the
light. The terminal part of outer segment is embedded in the pigment epithelium. The inner
segment of rod cell is bottle in shape with the length is 32 micrometer. Both of them have the
thickness of 1.5 micrometer. The outer and inner segment is connected by a narrow neck like
structure. The terminal part of inner segment has the shape like spherule called as rod spherule
which synapses to the outer plexiform layer. Electrone microscopy shows that the outer segment is
Figure-13 Retina
composed by membraneous lamellae that are arranged in parallel manner. The rod cells are
sensitive to the dim light but it is insensistive to the bright light and color.
Figure-14 The ultramicroscopy structure of retina.
Photoreception by rods begins with absorption of light by rhodopsin, which comprises the
transmembrane protein opsin bound to cis retinal, the aldehyde form of vitamin A. Absoption of
light causes isomerization of the retinal moiety which then dissociates from opsin. This bleeching
yields activated opsin which facilitates binding of guanosine triphosphate (GTP) to the alpha
subunit of a trimeric G protein called transducin. The resulting GTP-Gactives cyclic guanosine
monophosphate phosphodiesterase, an enzyme that catalyzes the breakdown of 3’,5’-cGMP.
cGMP opens Na+ channels in the plasmalemma of rod cells. During the dark phase, Na+ ions are
pumps out of the inner segment and enter the outer segment of the rods through gated Na +
channels. The presence of Na+ in the outer segment results in the release of neurotransmitter
substance into the synapse with the bipolar cells. The light induced activation of cGMP
phosphodiesterase depletes cGMP levels, consequently, the Na+ gate channels close, and the rods
become hyperpolarized. This event results in the inhibition of neurotransmitter release into the
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synapse with the bipolar cells. During the next dark phase the level of cGMP is regenerated, the
Na+ion channels are reopened and ion flow resumes as before. Light induced hyperpolarization
causes the signal to be transmitted through various cell layers to the ganglion cells where the
signal generates an action potential along the axons to the brain.
The structure of cone cells are similar to the rod cells, however its apical terminal of outer
segment is shaped more like a cone than a rod. The nuclei of cone cells are bigger than rod cells.
The inner segment of cone has the shape like bottle with the cone pedicle at its terminal part.
The cone cells are activated by bright light and produce greater visual activity than that of
rod cells. There are 3 types of cones each containing a different variety of photopigment iodopsin.
Each variety of iodopsin has amaximum sensitivity to red, green and blue.
External limiting membrane is not a membrane but it is a zonulae adherentes between
Muller cells and photoreceptor. Outer nuclear layer consists of the nuclei of rod and cone cells.
Outer plexiform layer is a synapse between axons of rod and cone cells with dendrites of bipolar
and horizontal cells.
Inner nuclear layer consist of the nuclei and body of bipolar, horizontal, amacrine and
Muller cells. Axon of bipolar cells pass vertically into the inner plexiform layer and synapses to
the dendrites of ganglion cells. The horizontal cells have the body bigger than bipolar cells. Its
dendrite synapses to cone pedicles. The amacrine cells have the shape like plump fruit with one
processus toward to the inner plexiform layer and make synapse with several ganglion cells.
Muller cells, also called as retinal gliocytes, have the giant size with the nuclei located in the inner
nuclear layer. The cytoplasm processes of Muller cells pass toward to the external and internal
limitans layer.
The processes of amacrine, bipolar and ganglion cells are intermingled in the inner
plexiform layer. Axodendritic synapses between axons of bipolar cells and dendrites of ganglion
cells are also located in this layer.
Ganglion layer consists of body and nuclei of ganglion cells. Ganglion cells is the large
cells similar to the neuronal cells in the brain which have the Nissl bodies. Axons of these neurons
pass to the nerve fiber layer. Hyperpolarization of the rods and cones activates the ganglion cells,
which then generate an action potential that is passed to the brain via visual relay system.
Optic nerve fiber layer is formed by unmyelinated axons of the ganglion cells. The inner
lmiting membrane is the basal laminae of the Muller cells that separates the retina from the vitreus
body.
REFRACTORY MEDIA
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The refractory media is the transparant structures which is passed by the light to reach the
retina. The components of refraction media are cornea, anterior and posterior chamber of eye, lens
and vitreus body.
THE ACCESSORY STRUCTURES OF EYE
The eye is located in the bone space that opens to the anterior. This anterior cleft is
covered by superior and inferior eyelids that meet in the center, called as palpebral fissure. The
transparent mucous membrane, known as the conjunctiva, lines the inner surface of the eyelid and
it is called as palpebral conjunctiva. The accessory structures of the eye consist of palpebrae,
conjunctiva and lacrimal glands.
THE EYELIDS
The eyelids are formed as folds of skin that cover the anterior surface of the eye. The
eyelids consists of skin in the outer part, fibrous connective tissue (tarsus) and sebaceous gland
(Meibomian) in the middle part and mucose membrane in the inner part. Stratified squamous
epithelium of skin covers their external surface whereas at the palpebral fissure, palpebral
conjunctiva covers the inner surface. Sweat glands are located in the skin of the eyelids, as are fine
hairs and sebaceous glands. The dermis of eyelids is thinner than in most skin, contains numerous
elastic fibers and is without fat. Dermis also contains the skeletal muscle, orbicularis oculi muscle.
The margins of the eyelids contain eyelashes arranged in row of three or four, but they are without
arrector pili muscle. Modified sweat glands called as glands of Moll, form a simple spiral before
opening into the eyelash follicles. The other smaller modified sebaceous glands, the glands of
Zeiss are associated with eyelashes and secrete their product into the eyelash follicles The eyelids
are supported by a framework of tarsal plates Meibomian glands, modified sebaceous glands
located in the tarsus of each lid, open on the free edge of the lid. The oily substance secreted by
these glands becomes incorporated into the tear film and impedes evaporation of the tears. In the
posterior of secreted duct of Meibomian glands there is a continuation of orbicularis oculi muscle
known as ciliary muscle of Riolani.
Figure-15 Palpebra (Eyelids)
CONJUNCTIVA (Fig-15)
Conjunctiva is a transparant mucous membrane, lines the inner surface of the eyelids
(known as palpebral conjunctiva) and covers the sclera of anterior portion of the eye (bulbar
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conjunctiva). Conjunctiva is composed of a stratified columnar epithelium that contains goblet
cells overlying a basal lamina and a lamina propria composed of loose connective tissue.
Sectretion of goblet cells become a part of the tear film, which aids in lubricating and protecting
the epithelium of anterior eye. At the corneoscleral junction, where the cornea begins, the
conjunctiva continues as the strafied squamous corneal epithelium and is devoid of goblet cells.
Conjunctivitis is an inflammation of the conjunctia usually associated with hyperemia and
a discharge. It may be caused by a number of bacterial agents, viruses, allergens and parasitic
organisms.
LACRIMAL GLANDS (Fig-16)
The lacrimal glands lies in the lacrimal fossa located within orb, superior and lateral to the
orb. The shape of lacrimal gland is like almond, a serous compound tubuloalveolar gland that
resembles the parotis glands. Myoepithel completely surround the secretory portions. The gland
secretes its product through 10-15 excretory duct to the lateral portion of superior conjunctival
fornix.
Figure-16 Lacrimal glands
Lacrimal fluid (tears) is composed mostly of water. This sterile fluid, containing lysozyme, an antibacterial
agent, passes through the secretory duct to enter the conjunctival sac. The upper eyelids, by blinking, wash
the tears over the anterior portion of sclera and cornea, thus keeping them moist and protect them from
dehydration. The lacrimal fluid is wiped in a medial direction and enters the lacrimal puncta, an aperture
located in each of the medial margins of superior and inferior eyelids. The puncta of each eyelid leads
directly to lacrimal canaliculi, which join into a common conduit that leads to the lacrimal sac. The wall of
the lacrimal canaliculi are lined by stratified squamous epithelium. The lacrimal sac is the dilated superior
portions of the nasolacrimal duct. It is lined by psuedostratified ciliated columnar epithelium. The inferior
continuation of the lacrimal sac is the nasolacrimal duct, also lined by pseudostarfied ciliated columnar
epithelium. This duct carries the lacrimal fluid into the inferior meatus located in the floor of the nasal
cavity.
TELINGA
PENDAHULUAN
Telinga merupakan organ pendengaran sekaligus juga organ keseimbangan. Telinga terdiri
atas 3 bagian yaitu telinga luar, tengah dan dalam (Gb-1). Gelombang suara yang diterima oleh
telinga luar di ubah menjadi getaran mekanis oleh membran timpani. Getaran ini kemudian di
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perkuat oleh tulang-tulang padat di ruang telinga tengah (tympanic cavity) dan diteruskan ke
telinga dalam. Telinga dalam merupakan ruangan labirin tulang yang diisi oleh cairan perilimf
yang berakhir pada rumah siput / koklea (cochlea). Di dalam labirin tulang terdapat labirin
membran tempat terjadinya mekanisme vestibular yang bertanggung jawab untuk pendengaran
dan pemeliharaan keseimbangan. Rangsang sensorik yang masuk ke dalam seluruh alat-alat
vestibular diteruskan ke dalam otak oleh saraf akustik (N.VIII).
TELINGA LUAR
Telinga luar terdiri atas daun telinga (auricle/pinna), liang telinga luar (meatus accusticus externus) dan gendang telinga (membran timpani) (Gb-1).
Daun telinga /aurikula (Gb-2) disusun oleh tulang rawan elastin yang ditutupi oleh kulit tipis
yang melekat erat pada tulang rawan. Dalam lapisan subkutis terdapat beberapa lembar otot lurik
yang pada manusia rudimenter (sisa perkembangan), akan tetapi pada binatang yang lebih rendah
yang mampu menggerakan daun telinganya, otot lurik ini lebih menonjol.
Liang telinga luar (Gb-1 dan Gb-3) merupakan suatu saluran yang terbentang dari daun telinga
melintasi tulang timpani hingga permukaan luar membran timpani. Bagian permukaannya
mengandung tulang rawan elastin dan ditutupi oleh kulit yang mengandung folikel rambut,
kelenjar sebasea dan modifikasi kelenjar keringat yang dikenal sebagai kelenjar serumen. Sekret
kelenjar sebacea bersama sekret kelenjar serumen merupakan komponen penyusun serumen.
Serumen merupakan materi bewarna coklat seperti lilin dengan rasa pahit dan berfungsi sebagai
pelindung.
Membran timpani (Gb-4) menutup ujung dalam meatus akustiskus eksterna. Permukaan luarnya
ditutupi oleh lapisan tipis epidermis yang berasal dari ectoderm, sedangkan lapisan sebelah dalam
disusun oleh epitel selapis gepeng atau kuboid rendah turunan dari endoderm. Di antara keduanya
terdapat serat-serat kolagen, elastis dan fibroblas. Gendang telinga menerima gelombang suara yang
di sampaikan lewat udara lewat liang telinga luar. Gelombang suara ini akan menggetarkan
membran timpani. Gelombang suara lalu diubah menjadi energi mekanik yang diteruskan ke tulangtulang pendengaran di telinga tengah.
TELINGA TENGAH (Gb-1)
Telinga tengah atau rongga telinga adalah suatu ruang yang terisi udara yang terletak di bagian
petrosum tulang pendengaran. Ruang ini berbatasan di sebelah posterior dengan ruang-ruang udara
mastoid dan disebelah anterior dengan faring melalui saluran (tuba auditiva) Eustachius.
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Epitel yang melapisi rongga timpani dan setiap bangunan di dalamnya merupakan epitel selapis
gepeng atau kuboid rendah, tetapi di bagian anterior pada pada celah tuba auditiva (tuba
Eustachius) epitelnya selapis silindris bersilia. Lamina propria tipis dan menyatu dengan
periosteum.
Di bagian dalam rongga ini terdapat 3 jenis tulang pendengaran (Gb-4) yaitu tulang maleus,
inkus dan stapes. Ketiga tulang ini merupakan tulang kompak tanpa rongga sumsum tulang. Tulang
maleus melekat pada membran timpani. Tulang maleus dan inkus tergantung pada ligamen tipis di
atap ruang timpani. Lempeng dasar stapes melekat pada tingkap celah oval (fenestra ovalis) pada
dinding dalam. Ada 2 otot kecil yang berhubungan dengan ketiga tulang pendengaran. Otot tensor
timpani terletak dalam saluran di atas tuba auditiva, tendonya berjalan mula-mula ke arah posterior
kemudian mengait sekeliling sebuah tonjol tulang kecil untuk melintasi rongga timpani dari dinding
medial ke lateral untuk berinsersi ke dalam gagang maleus. Tendo otot stapedius berjalan dari
tonjolan tulang berbentuk piramid dalam dinding posterior dan berjalan anterior untuk berinsersi ke
dalam leher stapes. Otot-otot ini berfungsi protektif dengan cara meredam getaran-getaran
berfrekuensi tinggi.
Tingkap oval (Gb-4) pada dinding medial ditutupi oleh lempeng dasar stapes, memisahkan
rongga timpani dari perilimf dalam skal vestibuli koklea. Oleh karenanya getaran-getaran membrana
timpani diteruskan oleh rangkaian tulang-tulang pendengaran ke perilimf telinga dalam. Untuk
menjaga keseimbangan tekanan di rongga-rongga perilimf terdapat suatu katup pengaman yang
terletak dalam dinding medial rongga timpani di bawah dan belakang tingkap oval dan diliputi oleh
suatu membran elastis yang dikenal sebagai tingkap bulat (fenestra rotundum)(Gb-4). Membran ini
memisahkan rongga timpani dari perilimf dalam skala timpani koklea.
Tuba auditiva (Eustachius) (Gb-1) menghubungkan rongga timpani dengan nasofarings
lumennya gepeng, dengan dinding medial dan lateral bagian tulang rawan biasanya saling
berhadapan menutup lumen. Epitelnya bervariasi dari epitel bertingkat, selapis silindris bersilia
dengan sel goblet dekat farings. Dengan menelan dinding tuba saling terpisah sehingga lumen
terbuka dan udara dapat masuk ke rongga telinga tengah. Dengan demikian tekanan udara pada
kedua sisi membran timpani menjadi seimbang.
TELINGA DALAM (Gb-1 dan Gb-5)
Telinga dalam adalah suatu sistem saluran dan rongga di dalam pars petrosum tulang
temporalis. Telinga tengah di bentuk oleh labirin tulang (labirin oseosa) yang di da-lamnya
terdapat labirin membranasea. Labirin tulang berisi cairan perilimf sedangkan labirin
membranasea berisi cairan endolimf.
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LABIRIN TULANG (Gb-1 dan Gb-5)
Labirin tulang terdiri atas 3 komponen yaitu kanalis semisirkularis, vestibulum, dan koklea
tulang. Labirin tulang ini di sebelah luar berbatasan dengan endosteum, sedangkan di bagian
dalam dipisahkan dari labirin membranasea yang terdapat di dalam labirin tulang oleh ruang
perilimf yang berisi cairan endolimf.
Vestibulum merupakan bagian tengah labirin tulang, yang berhubungan dengan rongga
timpani melalui suatu membran yang dikenal sebagai tingkap oval (fenestra ovale). Ke dalam
vestibulum bermuara 3 buah kanalis semisirkularis yaitu kanalis semisirkularis anterior, posterior
dan lateral yang masing-masing saling tegak lurus. Setiap saluran semisirkularis mempunyai
pelebaran atau ampula. Walaupun ada 3 saluran tetapi muaranya hanya lima dan bukan enam,
karena ujung posterior saluran posterior yang tidak berampula menyatu dengan ujung medial
saluran anterior yang tidak bermapula dan bermuara ke dalam bagian medial vestibulum oleh
krus kommune. Ke arah anterior rongga vestibulum berhubungan dengan koklea tulang dan
tingkap bulat (fenestra rotundum).
Koklea (Gb-1, Gb-4, Gb-5 dan Gb-6) merupakan tabung berpilin mirip rumah siput. Bentuk
keseluruhannya mirip kerucut dengan dua tiga-perempat putaran. Sumbu koklea tulang di sebut
mediolus. Tonjolan tulang yang terjulur dari modiolus membentuk rabung spiral dengan suatu
tumpukan tulang yang disebut lamina spiralis. Lamina spiralis ini terdapat pembuluh darah dan
ganglion spiralis, yang merupakan bagian koklear nervus akustikus.
LABIRIN MEMBRANASEA (Gb-5 dan Gb-6)
Labirin membransea terletak di dalam labirin tulang, merupakan suatu sistem saluran yang
saling berhubungan dilapisi epitel dan mengandung endolimf. Labirin ini dipisahkan dari labirin
tulang oleh ruang perilimf yang berisi cairan perilimf. Pada beberapa tempat terdapat lembaranlembaran jaringan ikat yang mengandung pembuluh darah melintasi ruang perilimf untuk
menggantung labirin membranasea.
Labirin membranasea terdiri atas:
1. Kanalis semisirkularis membranasea
2. Ultrikulus
3. Sakulus
4. Duktus endolimfatikus merupakan gabungan duktus ultrikularis dan duktus sakularis.
5. Sakus endolimfatikus merupakan ujung buntu duktus endolimfatikus
6. Duktus reuniens, saluran kecil penghubung antara sakulus dengan duktus koklearis
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7. Duktus koklearis mengandung organ Corti yang merupakan organ pendengaran.
Terdapat badan-badan akhir saraf sensorik dalam ampula saluran semisirkularis (krista
ampularis) (Gb-7) dan dalam ultrikulus dan sakulus (makula sakuli dan ultrikuli) (Gb-8)
yang berfungsi sebagai indera statik dan kinetik.
SAKULUS DAN ULTRIKULUS (Gb-5, Gb7 dan Gb-8)
Dinding sakulus dan ultrikulus dibentuk oleh lapisan jaringan ikat tebal yang mengandung
pembuluh darah, sedangkan lapisan dalamnya dilapisi epitel selapis gepeng sampai selapis kuboid
rendah. Pada sakulus dan ultrikulus terdapat reseptor sensorik yang disebut makula sakuli dan
makula ultrikuli. Makula sakuli terletak paling banyak pada dinding sehingga berfungsi untuk
mendeteksi percepatan vertikal lurus sementara makula ultrikuli terletak kebanyakan di lantai
/dasar sehingga berfungsi untuk mendeteksi percepatan horizontal lurus.
Makula disusun oleh 2 jenis sel neuroepitel (disebut sel rambut) yaitu tipe I dan II (Gb-9)
serta sel penyokong (Gb7) yang duduk di lamina basal.Serat-serat saraf dari bagian vestibular
nervus vestibulo-akustikus (N.VIII) akan mempersarafi sel-sel neuroepitel ini.
Sel rambut I berbentuk seperti kerucut dengan bagian dasar yang membulat berisi inti dan
leher yang pendek. Sel ini dikelilingi suatu jala terdiri atas badan akhir saraf dengan beberapa
serat saraf eferen, mungkin bersifat penghambat/ inhibitorik. Sel rambut tipe II berbentuk
silindris dengan badan akhir saraf aferen maupun eferen menempel pada bagian bawahnya.
Kedua sel ini mengandung stereosilia pada apikal, sedangkan pada bagian tepi stereosilia
terdapat kinosilia. Sel penyokong (sustentakular) merupakan sel berbentuk silindris tinggi,
terletak pada lamina basal dan mempunyai mikrovili pada permukaan apikal dengan beberapa
granul sekretoris.
Pada permukaan makula (Gb-7) terdapat suatu lapisan gelatin dengan ketebalan 22
mikrometer yang dikenal sebagai membran otolitik. Membran ini mengandung banyak badanbadan kristal yang kecil yang disebut otokonia atau otolit yang mengandung kalsium karbonat
dan suatu protein. Mikrovili pada sel penyokong dan stereosilia serta kinosilia sel rambut
terbenam dalam membran otolitik. Perubahan posisi kepala mengakibatkan perubahan dalam
tekanan atau tegangan dalam membran otolitik dengan akibat terjadi rangsangan pada sel
rambut. Rangsangan ini diterima oleh badan akhir saraf yang terletak di antara sel-sel rambut.
KANALIS SEMISIRKULARIS (Gb-5)
Kanalis semisirkularis membranasea mempunyai penampang yang oval. Pada permukaan
luarnya terdapat suatu ruang perilimf yang lebar dilalui oleh trabekula.
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Pada setiap kanalis semisirkularis ditemukan sebuah krista ampularis, yaitu badan akhir
saraf sensorik yang terdapat di dalam ampula (bagian yang melebar) kanalis (Gb-8). Tiap
krista ampularis di bentuk oleh sel-sel penyokong dan dua tipe sel rambut yang serupa dengan sel
rambut pada makula. Mikrovili, stereosilia dan kinosilianya terbenam dalam suatu massa
gelatinosa yang disebut kupula (Gb-8) serupa dengan membran otolitik tetapi tanpa otokonia.
Dalam krista ampularis, sel-sel rambutnya di rangsang oleh gerakan endolimf akibat
percepatan sudut kepala. Gerakan endolimf ini mengakibatkan tergeraknya stereosilia dan
kinosilia. Dalam makula sel-sel rambut juga terangsang tetapi perubahan posisi kepala dalam
ruang mengakibatkan suatu peningkatan atau penurunan tekanan pada sel-sel rambut oleh
membran otolitik.
KOKLEA (Gb-5, Gb-6 dan Gb- 10)
Koklea tulang berjalan spiral dengan 23/4 putaran sekiitar modiolus yang juga merupakan
tempat keluarnya lamina spiralis. Dari lamina spiralis menjulur ke dinding luar koklea suatu
membran basilaris. Pada tempat perlekatan membran basilaris ke dinding luar koklea terdapat
penebalan periosteum yang dikenal sebagai ligamentum spiralis. Di samping itu juga terdapat
membran vestibularis (Reissner) yang membentang sepanjang koklea dari lamina spiralis ke
dinding luar. Kedua membran ini akan membagi saluran koklea tulang menjadi tiga bagian yaitu
1. Ruangan atas (skala vestibuli)
2. Ruangan tengah (duktus koklearis)
3. Ruang bawah (skala timpani).
Antara skala vestibuli dengan duktus koklearis dipisahkan oleh membran vestibularis
(Reissner). Antara duktus koklearis dengan skala timpani dipisahkan oleh membran basilaris.
Skala vesibularis dan skala timpani mengandung perilimf dan di dindingnya terdiri atas jaringan
ikat yang dilapisi oleh selapis sel gepeng yaitu sel mesenkim, yang menyatu dengan periosteum
disebelah luarnya. Skala vestibularis berhubungan dengan ruang perilimf vestibularis dan akan
mencapai permukaan dalam fenestra ovalis. Skala timpani menjulur ke lateral fenestra rotundum
yang memisahkannya dengan ruang timpani. Pada apeks koklea skala vestibuli dan timpani akan
bertemu melalui suatu saluran sempit yang disebut helikotrema.
Duktus koklearis berhubungan dengan sakulus melalui duktus reuniens tetapi berakhir buntu
dekat helikotrema pada sekum kupulare.
Pada pertemuan antara lamina spiralis tulang dengan modiolus terdapat ganglion spiralis
yang sebagian diliputi tulang. Dari ganglion keluar berkas-berkas serat saraf yang menembus
tulang lamina spiralis untuk mencapai organ Corti. Periosteum di atas lamina spiralis menebal
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dan menonjol ke dalam duktus koklearis sebagai limbus spiralis. Pada bagian bawahnya menyatu
dengan membran basilaris.
Membran basilaris yang merupakan landasan organ Corti dibentuk oleh serat-serat kolagen.
Permukaan bawah yang menghadap ke skala timpani diliputi oleh jaringan ikat fibrosa yang
mengandung pembuluh darah dan sel mesotel.
Membran vestibularis merupakan suatu lembaran jaringan ikat tipis yang diliputi oleh epitel
selapis gepeng pada bagian yang menghadap skala vestibuli.
DUKTUS KOKLEARIS (Gb-5, Gb-6 dan Gb-10)
Epitel yang melapisi duktus koklearis beragam jenisnya tergantung pada lokasinya, diatas
membran vestibularis epitelnya gepeng dan mungkin mengandung pigmen, di atas limbus
epitelnya lebih tinggi dan tak beraturan. Di lateral epitelnya selapis silindris rendah dan di
bawahnya mengandung jaringan ikat yang banyak mengandung kapiler. Daerah ini disebut stria
vaskularis dan diduga tempat sekresi endolimf.
ORGAN CORTI (Gb-10 dan Gb-11)
Organ Corti terdiri atas sel-sel penyokong dan sel-sel rambut. Sel-sel yang terdapat di organ
Corti adalah
1. Sel tiang dalam merupakan sel berbentuk kerucut yang ramping dengan bagian basal
yang lebar mengandung inti, berdiri di atas membran basilaris serta bagian leher yang
sempit dan agak melebar di bagian apeks.
2. Sel tiang luar mempunyai bentuk yang serupa dengan sel tiang dalam hanya lebih
panjang. Di antara sel tiang dalam dan luar terdapat terowongan dalam.
3. Sel falangs luar merupakan sel berbentuk silindris yang melekat pada membrana
basilaris. Bagian puncaknya berbentuk mangkuk untuk menopang bagaian basal sel
rambut luar yang mengandung serat-serat saraf aferen dan eferen pada bagian
basalnya yang melintas di antara sel-sel falangs dalam untuk menuju ke sel-sel rambut
luar. Sel-sel falangs luar dan sel rambut luar terdapat dalam suatu ruang yaitu
terowongan Nuel. Ruang ini akan berhubungan dengan terowongan dalam.
4. Sel falangs dalam terletak berdampingan dengan sel tiang dalam. Seperti sel falangs
luar sel ini juga menyanggah sel rambut dalam.
5. Sel batas membatasi sisi dalam organ corti
6. Sel Hansen membatasi sisi luar organ Corti. Sel ini berbentuk silindris terletak antara
sel falangs luar dengan sel-sel Claudius yang berbentuk kuboid. Sel-sel Claudius ter-
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letak di atas sel-sel Boettcher yang berbentuk kuboid rendah.
Permukaan organ Corti diliputi oleh suatu membran yaitu membrana tektoria yang
merupakan suatu lembaran pita materi gelatinosa. Dalam keadaan hidup membran ini menyandar
di atas stereosilia sel-sel rambut.
GANGLION SPIRALIS (Gb-6, Gb-10 dan Gb-11)
Ganglion spiralis merupakan neuron bipolar dengan akson yang bermielin dan berjalan
bersama membentuk nervus akustikus. Dendrit yang bermielin berjalan dalam saluran-saluran
dalam tulang yang mengitari ganglion, kehilangan mielinnya dan berakhir dengan memasuki
organ Corti untuk selanjutnya berada di antara sel rambut. Bagian vestibular N VIII memberi
persarafan bagian lain labirin. Ganglionnya terletak dalam meatus akustikus internus tulang
temporal dan aksonnya berjalan bersama dengan akson dari yang berasal dari ganglion spiralis.
Dendrit-dendritnya berjalan ke ketiga kanalikulus semisirkularis dan ke makula sakuli dan
ultrikuli.
Telinga luar menangkap gelombang bunyi yang akan diubah menjadi getaran-getaran oleh
membran timpani. Getaran-getaran ini kemudian diteruskan oleh rangkaian tulang –tulang
pendengaran dalam telinga tengah ke perilimf dalam vestibulum, menimbulkan gelombang
tekanan dalam perilimf dengan pergerakan cairan dalam skala vestibuli dan skala timpani.
Membran timpani kedua pada tingkap bundar (fenestra rotundum) bergerak bebas sebagai katup
pengaman dalam pergerakan cairan ini, yang juga agak menggerakan duktus koklearis dengan
membran basilarisnya. Pergerakan ini kemudian menyebabkan tenaga penggunting terjadi antara
stereosilia sel-sel rambut dengan membran tektoria, sehingga terjadi stimulasi sel-sel rambut.
Tampaknya membran basilaris pada basis koklea peka terhadap bunyi berfrekuensi tinggi ,
sedangkan bunyi berfrekuensi rendah lebih diterima pada bagian lain duktus koklearis.
Rujukan
1. Wonodirekso, S dan Tambajong J (editor) (1990), Organ-Organ Indera Khusus dalam
Buku Ajar Histologi Leeson and Leeson (terjemahan), Edisi V, EGC, Jakarta,
Indonesia Hal.574-583.
2. Fawcett, D.W (1994), The Ear in: A Textbook of Histology (Bloom and Fawcett), 12th
edition, Chapman and Hall, New York, USA, pp. 919-941
3. diFiore, MSH (1981), Organs of Special Sense and Associated Structures, in Atlas of
Human Histology, 5th edition, Lea and Febiger, Philadelphia, USA, pp.256-257.
4. Young, B and Heath, J.W. (2000), Special Sense Organs in Wheater’s Functional
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Histology, 4th edition, Churchill Livingstone, London, UK, pp 380-405
5. Gartner, LP and Hiatt, J.L. (1997), Special Senses in: Color Textbook of Histology,
W.B. Saunder Company, USA, pp. 422-442
References
1. Wonodirekso, S dan Tambajong J (editor) (1990), Organ-Organ Indera Khusus dalam
Buku Ajar Histologi Leeson and Leeson (terjemahan), Edisi V, EGC, Jakarta,
Indonesia Hal.538-574.
2. Fawcett, D.W (1994), The Eye in: A Textbook of Histology (Bloom and Fawcett), 12th
edition, Chapman and Hall, New York, USA, pp. 872-916
3. diFiore, MSH (1981), Organs of Special Sense and Associated Structures, in Atlas of
Human Histology, 5th edition, Lea and Febiger, Philadelphia, USA, pp.248-256.
4. Young, B and Heath, J.W. (2000), Special Sense Organs in Wheater’s Functional
Histology, 4th edition, Churchill Livingstone, London, UK, pp 380-405
5. Gartner, LP and Hiatt, J.L. (1997), Special Senses in: Color Textbook of Histology,
W.B. Saunder Company, USA, pp. 422-442
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