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LECTURE NOTEMODULE OF SPECIAL SENSE

AN OVERVIEW IN THE HISTOLOGICAL ASPECT

Ahmad Aulia Jusuf, MD, PhD

Departement of HistologyFaculty of Medicine University of Indonesia

Jl. Salemba Raya 6 Jakarta2009

IntroductionThe 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

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.

Figure-1 The Eye

The bulb of eye is composed of

three tunics (coats)

1. Fibrous tunic (sclero-cornea

layer) which 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

Fig-2 The histological picture of the wall of eye ball

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

attached to the tunica fibrosa. Choroid consist of

Figure-6 Choroid

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

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

Figure-11 Optic Cup

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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-Gactives 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 accus-

ticus 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 tulang-

tulang 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 lembaran-

lembaran 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 badan-

badan 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

21

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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