MICROSCOPIC STRUCTURE AND DEVELOPMENT OF THE ORGAN OF VISION MICROSCOPIC STRUCTURE AND DEVELOPMENT OF THE ORGAN OF HEARING Lecture 9 General Medicine_3rd semester THE EYE AND REFRACTIVE (DIOPTRIC) MEDIA ACCESSORY STRUCTURES OF THE EYE OVERVIEW OF DEVELOPMENT OF THE EYE nthe eye na complex and highly specialized photosensitive organ that permits an naccurate analysis of the form, light intensity, and colour reflected from nobjects n nit consists of: n nthe eyeball (bulbus oculi) nthe accessory organs of the eye: - conjunctiva, - eyelids, - lacrimal apparatus (lacrimal gland with ducts, 2 lacrimal canaliculi - superior and inferior, lacrimal sac and nasal duct) - and oculomotor muscles on each side n nTHE EYEBALL n nresembles a sphere, lies in protective bony structure of the skull - the orbit n nanatomical description of the eyeball uses similar terms as description of nthe earth globe in geography n nmeridians or meridian planes or sections that transect the poles + nthe equator or equatorial plane or section oriented upright to the meridian planes nand halve them anterioposterior diameter 24 - 26 mm the eyeball is made up of: - a wall - a content polus ant. polus post. n. opticus axis bulbi ext. linea visus fovea centralis Zadní část – méně zakřivená (poloměr zakřivení 11-12 mm) – povrch tvoří bělima Přední část – vce zakřivená (poloměr zakřivení 7-8 mm) – tvoří průhledná rohovka Ze zadní část oční koule uprostřed a poněkud med. vystupuje n. opticus Předozadní průměr bulbu – 23-26 mm Vetikální a transversální průměry jsou o něco menší Pro orientaci na bulbu slouží myšlené čáry: přední a zadní pól oka propojují meridiani – poledníky kolmo na ně equator – rovník Poraněné místo lze při dg. popisu označit při pohledu zpředu na oko také číslicí hodinového číselníku bulbus_meridion the eyeball is made up of: - a wall - a content meridional section 001 ----------------------------- 2 hemispheric segments: the anterior the posterior meridians equator the wall: tunica externa tunica media tunica interna nexternal fibrous coat (layer) - tunica fibrosa - comprises the sclera and the cornea n nmiddle vascular coat (layer) - tunica vasculosa or the uveal tract -includes the choroid, ciliary body and iris n ninternal nervous coat (layer) - tunica nervosa or retina n nthe content of the eyeball are the aqueous humour, lens and vitreous body nare known as the refractive (dioptric) media n(in broader sense, the cornea is supposed as an integral part of the refractive media) n n3 well-defined spaces (compartments) are within the eyeball: n nthe anterior chamber - a space between the cornea and the iris and the anterior face of the lens that is filled with the aqueous humour n nthe posterior chamber - a slit-like shaped space between the iris, ciliary processes, zonular attachment and lens containing also the aqueous humour n nthe vitreous space - a compartment lying behind the lens and zonular attachment and retina; it is occupied by the vitreous body. F23_01 nTunica externa oculi - nexternal layer n nThe sclera n nopaque white coat of the eyeball noccupying five-sixth of the external nlayer n nconsists of dense fibrous nconnective tissue made up nmainly of the flat collagen bundles, na moderate amount of ground nsubstance, and a few fibroblasts n nCollagen bundles run parallel with the surface nof the eyeball and intersect in various ndirections n nexternally, the sclera is enveloped nwith fascial sheath - Tenon´s ncapsule n na delicate space between the sclera and ncapsule is known as Tenon´s space sclera kopie n The cornea n ncolourless, transparent and avascular segment of the external layer that occupies one-sixth of the tunic n n5 layers: §the corneal epithelium n a stratified squamous, and nonkeratinized, composed of 5-6 cell layers n numerous mitosis in the basal layer n is penetrated with dense free nerve endings n nthe Bowman´s membrane - 7-12 mm thick membrane that contributes to the stability n and strength of the cornea n it consists of collagen fibres crossing at random and intercellular substance n nthe substantia propria (stroma) - 90% of total thickness n formed by many lamellae (membranes) of collagen fibres that run parallel in the same layer n fibroblasts are called keratocytes n an amorphous metachromatic glycoprotein substance F23_04 nthe Descemet´s membrane - 5-10 mm n homogeneous structure composed of fine collagen filaments organized in a complex 3-D network n prominent in older persons n produced by the corneal endothelium n nthe corneal endothelium - a simple squamous epithelium that is continuous with the epithelium covering the anterior surface of the iris n nthe corneoscleral limbus (or junction) - an area of transition between the cornea n and the sclera nperipherally, the cornea and the iris meet each other in an angle - iridocorneal angle nfilled with trabecular meshwork = endothelium lined channels, they open into the canal of nSchlemm - regulates the outflow of the aqueous humour from the anterior chamber into blood prsegmentSchema kopie nTunica media oculi, vascular layer or the uveal tract n nthe choroid, ciliary body, and iris n nThe choroid n nis highly vascularized coat, composed of loose connective tissue, blood vessels and nmelanocytes (they give it its characteristic black colour), 0.1-0.2 mm thick n nit consists of 4 layers (laminae): nthe suprachoroidal lamina - a thin layer nof loose connective tissue rich in melanocytes, nfibroblasts and elastic fibres n nthe vessel layer - contains of arterioles nand venules n nthe choriocapillary layer - contains ncapillaries arranged in one layer and provides nnutrition of the retina n nBruch´s membrane (the lamina vitrea) – na hyaline membrane that separates the choriocapillary nlayer from the retina cevnatka F23_03 nThe ciliary body nis continuous thickened ring situated at the inner surface of the anterior portion of nthe sclera nit resembles a triangle on meridional sectinos none of its faces is in contact with vitreous body, one with the sclera, and the third with the nlens and the posterior chamber n na core of the ciliary body is formed by the ciliary muscle nis surrounded with loose connective tissue (rich in elastic fibres, vessels, and nmelanocytes) nfree surface of ciliary body is folded and sends off extensions oriented toward nthe lens - the ciliary processes n n sklerokorn kopie pars plicata pars radiata 011 nciliary muscle is smooth ncells run in 3 directions of: n - an inner circular group - muscle of Müller, n - a middle radial group, n - an outer meridional group n nby contractions of individual muscle groups, the volume of body and tension of the zonular fibres are nchanged what plays important role in visual accommodation n nsurface of the ciliary processes is covered with 2-layered epithelium, a ciliary part of nonnervous n(not photosensitive) portion of the retina nthe basal layer = a simple columnar cells rich in melanin (it corresponds to the pigment layer of the retina) nthe superficial layer = a simple columnar cells without pigment (it corresponds to the sensory layers of the nretina), it produces the aqueous humour n nfrom the ciliary processes emerge fibres (zonule fibres) nthat insert into the capsule of the lens and nanchor it in place corpusciliare prsegmentSchema kopie nThe iris nit lies in front of the lens and has form of diaphragm with central located round nopening - the pupilla; 100 mm thick nit has two margins: ciliary (at the ciliary body) and pupillary (at the pupilla) Smyslové orgány II - 32 nIt consists of: nthe anterior epithelium - a simple flat (the endothelium), nthe stroma - poorly vascularized, with few fibers and many fibroblasts and n melanocytes nthe posterior epithelium - a simple columnar and pigmented one (it is iridical n part of the nonnervous (not photosensitive) portion of the retina Bez názvu 1 kopie In addition, the iris contains 2 unstriped muscles: § the circular sphincter of the pupilla (it lies near the pupillary margin), § the radiating dilator of the pupilla (it lies near the ciliary margin). nTunica interna oculi, tunica nervosa ninternal nervous layer - retina n nthe retina lines the eyeball and ends at the margin of the pupil Øphotosensitive portion of the retina - 120–180 mm Ønot photosensitive portion of the retina - 20 - 25 mm (that is identical with n surface epithelium of the ciliary body and the posterior epithelium of the iris) n nthe ora serrata 003 nPhotosensitive portion of the retina npigment cells, cone and rod cells, bipolar cells, ganglion cells, horizontal cells, amacrine cells, and supporting ncells n npigment cells: are columnar in shape with a basal nucleus, basal aspects of cells adhere to Bruch´s membrane, apices have abundant extensions: microvilli and cylindrical sheaths that invest the tips of the rods and cones n the cytoplasm contains numerous melanin granules that may migrate from body into microvilli and cylindrical sheaths F23_16 § Rod and cone cells n are thin, elongated and highly specialized nerve cells (50 to 70 x 1.5 to 3.0 mm), they form the first neuron of the retina n nRod cells consist of: nTHE PERIPHERAL PART - serves as nphotoreceptive apparatus; it has two nsegments - the outer and the inner ones, nthat are separated each other by a constriction ncontaining an atypical kinocilium n nthe outer segment contains 600 to 1000 flattened nmembranous disks piled up like a stack of coins. The disks ncontain visual purple or rhodopsin n nthe inner segment - is rich in glycogen and local naccumulation of mitochondria and polyribosomes n nTHE CENTRAL PART - contains nucleus and n narrows into the thick process ending with n arborizations that contact the dendrites of n bipolar cells n approx. 120 millions, responsible for night vision n nThe cone cells have similar structure to that nof the rod cells but they are shorter and fatter, ncells synthesize photopigment iodopsin n nresponsible for visual discrimination and colour nvision - total number of cones is about 6-7 millions retina_bunky Smyslové orgány I - 16 F23_14 nBipolar cells: have small bodies, one dendrite and one neurit; represent the second neuron of the retina nGanglion cells: show large bodies, numerous dendrites and single axon; cells represent the third neuron of the retina nHorizontal cells - association nerve cells that establish contact between different photoreceptors. Cells are located in the internal nuclear layer (near to the outer plexiform layer) nAmacrine cells - association nerve cells that establish contact between the ganglion cells. Cells are located in the internal nuclear layer (near to the inner plexiform layer) n nSupporting cells: are modified glial ones known as Müller cells n cells are columnar in shape and their bodies have many depressions due to neurons n Mueller cells occupy practically the entire retina, e.g. its part between the outer and inner limiting membranes (which are formed by their outer or inner cell bases) Nuclei of Müller cells are in the internal nuclear layer F23_12 ncells described above show layered (laminated) organization in the retina nin direction from the Bruch´s membrane to the vitreous space, 10 distinct layers nare to distinguish n1. Pigment epithelium (layer) n n2. Layer of rods and cones = the peripheral parts of the rod a cone cells n n3. External limiting membrane = outer bases of Müller cells THE 1ST NEURON n n4. External nuclear layer= nuclei of rod and cone cells n n5. External plexiform layer - contains synapses between the rod (cone) cells and nbipolar cells n n6. Internal nuclear layer= bipolar cells (it also contains nuclei of Müller cells, bodies n of horizontal and amacrine cells) THE 2ND NEURON n n7. Internal plexiform layer - contains synapses between the bipolar and ganglion ncells n n8. Ganglion cell layer = bodies of multipolar neurons THE 3RD NEURON n n9. Nerve fiber layer = axons of multipolar neurons converging to blind spot n n10. Internal limiting membrane = inner bases of Müller cells retina_schema Smyslové orgány I - 32 F23_10 005 006 nHuman retina (similar to retina of all vertebrates) is inverse ne.g. light must pass through most layers of retina (in all, through 7 layers - nfrom 10th to 3rd ones) than is absorbed of peripheral parts of rods and ncones n F23_11 nRegional differences of nthe retina n nthe fovea centralis and blind spot nshow modified microscopic structure n nfovea centralis - macula lutea n is a depressions lying in the optical axis, in whose centre only cones occur (bipolar and ganglion cells lie at the periphery) - light is directly absorbed with photoreceptors n n fovea centralis is responsible for maximal visual acuity F23_02 009 n blind spot (or papilla) - is a site of leaving axons of ganglion cells no photoreceptors Bez názvu 1 kopie 010 nREFRACTIVE MEDIA OF THE EYEBALL n nare characterized by high transparency and refractivity n nthe cornea (it has been described above), the aqueous humour, the lens, and the nvitreous body n nThe aqueous humour na transparent fluid having composition similar to blood plasma ncontains less than 0.1 % proteins (plasma has approx. 7 %) n ZonZinnii nThe lens nis biconvex and elastic body, located nbehind the iris n nlens capsule - 10-20 mm thick, homogeneous, refractive (carbohydrates and collagen IV) n nlens epithelium - occurs only on the anterior aspect of the lens beneath the capsule (a single flat to columnar epithelium) n nlens fibers that are highly specialized and differentiated cells arising by transformation of the lens epithelium at the equator n contain no nuclei and cell organelles, and reach 7-10 mm in length, 5-7 mm in width n lens fibers are rich in special proteins - crystallins and filensin n nthe lens is suspended on zonular nfibers that insert on the ciliary body n 003 004 F23_05 nThe vitreous body noccupies the vitreous spacethe vitreous body is of transparent, gel-like nconsistence nmain components are water (99%), collagen and heavily hydrated glycosamino- nglycans (rich in hyaluronic acid) nACCESSORY ORGANS OF THE EYE n nConjunctiva - is a thin, transparent mucous membrane that covers the anterior portion of the eye to the cornea and the internal surface of the eyelids n it consists of a stratified columnar epithelium with numerous goblet cells and lamina propria of the loose connective tissue n nEyelids - are movable folds that protect the eye n the core of the eyelid consists of the tarsal plate n (dense fibrous connective tissue) and orbicular n ocular muscle situated ventrally to the tarsal plate n ventral aspect - is covered with thin skin, n dorsal aspect - is covered with the conjunctiva n n Glands of the eyelids: n n - the meibomian glands are long sebaceous n glands placed in the tarsal plate, their ducts open n direct on margo liber of the eyelid (they never n communicate with hair follicles) n n - the glands of Zeiss are modified sebaceous glands n connected with the hair follicles of the eyelashes n n - the glands of Moll are sweat, tubular and n unbranched, they open into the hair follicles of n the eyelashes F23_17 víčko kopie tunica conjunctiva 006 eyelid nThe lacrimal apparatus n nthe lacrimal gland with ducts: serous gland similar to parotid, which is composed of several small lobes formed with serous acini; the secretory ducts open into the superior conjunctival fornix. Secretions of the lacrimal gland are tears n n tears moisten the surface of the bulb and conjunctiva and are collected near the inner eye canthus §lacus lacrimalis § §the lacrimal canaliculi drain (through lacrimal puncta) tears in the lacrimal sac. Lacrimal ductuli are two (superior and inferior), they have length 8 mm and diameter of 1 mm and are lined with a stratified squamous epithelium § §the lacrimal sac - is dilated part of the lacrimal drainage system located in the bone. Its continuation forms § §the nasolacrimal duct which opens into the inferior meatus lateral to the inferior turbinate n (the lacrimal sac and nasolacrimal duct are lined with a pseudostratified ciliated epithelium) n nOculomotor muscles F23_18 nDEVELOPMENT OF THE EYE n nthe eye primordia appear very early (about on the 22nd day) as optic sulci in the neural folds at the site of forebrain n nas neural folds fuse, the optic sulci evaginate to form paired hollow diverticula called optic vesicles n nthe optic vesicle then grows laterally on each side and its connection with nthe forebrain becomes to narrow and forms optic stalk n Smyslové orgány I - 25 nlater both optic vesicles invaginate and become double-walled, cup-like structures - optic ncusps nthey reach up to the surface ectoderm that becomes thickened and form lens placode n nthe central region of each lens placode invaginates and sinks below the surface, forming a lens pit. nthe edges of the lens pit gradually come together and fuse to form a spherical lens vesicle n nRemember: the lens vesicle and optic cusp derive from the ectoderm resp. neuroectoderm and are completely surrounded with head mesenchyme Smyslové orgány I - 26 nThe retina n ndevelops from the double-layered optic cusp n nthe outer layer becomes the pigment epithelium, and the inner layer differentiates into the remaining layers (rod and cone, bipolar, and ganglion cells) n nintraretinal space, presented initially between the outer and inner layers gradually disappears so that the pigment epithelium and remaining retinal layers fuse n nthe junction of definitive pigment layer with the layer of rods and cones is not so firm as elsewhere so that detachment of retina may occur (after traumatic injury of the eye) n nthe edge of the optic cusp gives rise to the ciliary epithelium and posterior epithelium of the iris is identical with the not photosensitive portion of the retina Smyslové orgány I - 27 Smyslové orgány I - 28 nThe middle and external layers ndevelop from the mesenchyma that envelops the external surface of the noptic cusp n nThe lens develops from the lens vesicle nthe anterior wall of the vesicle gives rise to the anterior epithelium of the nlens, the cells of the posterior wall gradually lengthen and form lens fibers nthe lens capsule is produced by the epithelial cells of both aspects of the nlens vesicle nnutrition of the lens during development is provided by the hyaloid artery, na branch of the ophthalmic artery nrests of the hyaloid artery found in vitreous body are known as hyaloid canal n(Cloqueti) n nThe anterior eye chamber originates as cleft-like space that forms between nthe lens and the surface ectoderm n nThe cornea develops from the surface ectoderm and mesenchyme adhering nto it after forming of the anterior eye chamber n nthe stalk of the optic cusp becomes the optic nerve Smyslové orgány I - 29 F23_13 MICROSCOPIC STRUCTURE OF THE EAR (VESTIBULOCOCHLEAR ORGAN) Major structural differences between the statokinetic and acoustic compartments OVERVIEW OF DEVELOPMENT OF THE VESTIBULOCOCHLEAR ORGAN nthe ear (vestibulocochlear organ) has 2 main functions: nit serves to hearing nit serves to maintain equilibrium n nthe ear consists of 3 parts: n nthe external ear - nreceiver of sound waves n nthe middle ear - nconducts acoustic waves from n air to nbone and it amplifies them n nthe inner ear - ntransduction of acoustic nwaves to specific nerve nimpulses Smyslové orgány II - 18 nEXTERNAL EAR n nthe auricle (pinna), the external auditory nmeatus, and the tympanic membrane n nThe auricle: contains as a core tissue elastic cartilage that is covered by thin skin with hairs, sebaceous glands and few eccrine sweat glands n nThe external auditory meatus - is a somewhat flattened canal extending from the surface into the temporal bone up to the tympanic membrane nmeatus is supported by elastic cartilage (in the outer 1/3 and bone tissue (in inner remaining 2/3) lumen is lined with thin skin containing hair follicles, sebaceous glands and modified sweat glands - the ceruminous glands n produce earwax - the cerumen (a brownish, semisolid mixture of fats and waxes) n nThe tympanic membrane - 3 layers n a core of the membrane = plate of dense connective tissue n a thin epidermis n a thin mucous coat covered with a simple cuboidal epithelium nthe anterior upper quadrant of the tympanic nSchrapnell´s membrane n nFunction: the tympanic membrane transmits sound nvibrations to the ossicles of the middle ear Smyslové orgány II - 18 nMIDDLE EAR n nthe tympanic cavity, ossicles and auditory n(Eustachian) tube n nthe tympanic cavity: between the tympanic membrane and medial boundary at the bony wall of the inner ear n by a simple squamous epithelium n (except region near the tympanic membrane and the beginning of the auditory tube where is a simple cuboidal epithelium) n nOssicles: the malleus, incus, and stapes n are composed of lamellar bone tissue n they articulate each other via small synovial joints n surface of ossicles covers thin mucous coat n nFunction: ossicles transmit the mechanical vibrations generated in the tympanic membrane to the inner ear ( on the oval window) n nThe auditory tube (eustachian tube) n portion of tube near the middle ear is supported by the temporal bone, portion near the nasopharynx by a spiral elastic cartilage n the tube is lined with a thin mucosa covered by a low ciliated columnar epithelium in portion near the middle ear and by a in its nasopharyngeal end pseudostratified columnar epithelium n the lamina propria is thin and becomes thickened to the pharyngeal opening where may be infiltrated with lymphocytes - tubal tonsil (of Gerlach) n nFunction: the auditory tube serves to equalise pressure in ntympanic cavity and outside world Smyslové orgány II - 18 nINTERNAL EAR n nwithin petrous portion of the ntemporal bone n ntwo labyrinths: Øthe bony (osseous) Øthe membranous n nthe bony labyrinth nincludes series of spaces: n n- the vestibule n- 3 semicircular canals n- cochlea Smyslové orgány II - 18 Smyslové orgány II - 20 nthe membranous nlabyrinth n Øthe utricle and the saccule n - are housed within the vestibule Ø Øthe 3 semicircular ducts - nlie within semicircular canals Ø Øcochlear duct (scala media) n - is housed within the cochlea n nindividual segments are ninterconnected each other n nspace between the bony and nmembranous labyrinths = nperilymphatic space Smyslové orgány II - 20 F23_20 Bez názvu 1 kopie nthe membranous labyrinth n nis lined with simple epithelium (ectodermic norigin) n nfrom site to site is differentiated in specialized nsensory fields: n Øthe maculae (in the utricle and saccule) - nserve to vestibular function Ø Øthe cristae (in the semicircular ducts) nserve vestibular function Ø Øthe organ of Corti (in the cochlear duct) - nserves auditory function n nare continuous each other ncontain endolymph ( fluid with low sodium and high potassium content; the protein concentration is extremely low) n na narrow space between the membranous and bony labyrinths is lined with flat cells - and is filled with perilymph n (has similar ionic composition as the endolymph) Smyslové orgány II - 20 nSaccule and utricle n nboth compartments are bound to the periosteum of the bony labyrinth by thin nstrands of dense fibrous connective tissue n ntheir wall is composed of n- a thin sheath of connective tissue n- a simple squamous epithelium n nthe epithelium is in one site higher and forms nsensory field - the macula n(of the saccule/utricle) n nmaculae consist of n receptor hair cells n supporting cells n (and nerve endings) n nhair cells - on apices have 40 - 80 long rigid stereocilia (highly specialized microvilli) arranged in rows of nincreasing length and one kinocilium (probably immotile); cells contain numerous mitochondria, a well- ndeveloped Golgi apparatus, and an abundance of smooth endoplasmic reticulum n2 types of hair cells are distinguished (according to the form of their afferent innervation: ntype I - have a large, cup-shaped ending surrounding most of the base of the cell, ntype II- have many small afferent endings n nSupporting cells - are columnar in shape with microvilli on their apical surfaces, between hair cells HISTOLOGY OF THE MEMBRANOUS LABYRINTH 014 nsurface of both maculae - covered with a thick gelatinous glycoprotein layer, secreted by nsupporting cells nit contains deposits of calcium carbonate crystals = otoliths or otoconia n nFunction: the maculae nrespond to linear nacceleration (by changes nin position of the head, nthe otoliths displace nwithin the glycoprotein nmembrane and deformate nstereocilia of the hair cells, nthe deformation results in naction potentials that nare carried to the CNS F23_21 013 macula nSemicircular ducts n nare 3 noriented in main planes of body nreceptor area occupies dilated end of each duct = the ampulla and has an nelongated and ridge like form - crista ampullaris n nstructurally, cristae are similar to nmaculae nbut glycoprotein layer is substantially nthicker and has conical form - a ncupula nit does not contain otoliths Smyslové orgány II - 21 crista F23_23 Function: the cristae respond to angular acceleration (increase or decrease) changes of angular acceleration cause a flow of fluid in the semicircular ducts that induces a movement of the cupula over the crista ampullaris and results in bending of the stereocilia on hair cells is followed by arising of action potentials nCochlear duct nthis compartment of the membranous labyrinth appears to be as diverticulum of the saccule, it nis blind and filled with endolymph, about 35 mm nlong nis housed within cochlea nit serves as sound receptor The cochlea (saggital section): the cochlear spiral canal - is about 35 mm in total length and makes 2.5 turns around bony core the modiolus (is penetrated by spaces (chanels) containing blood vessels and cell bodies and processes of acoustic branch of the 8th cranial nerve - spiral ganglion) the osseous spiral lamina - extends laterally from the modiolus 3 spaces are in the cochlear spiral canal: Smyslové orgány II - 22 -- the scala vestibuli - turned to the apical part of the cochlea -- the scala media = cochlear duct -- the scala tympani - turned to the base of the cochlea both scalae communicate each other via opening known as the helicotrema - situated at the apex of the cochlea around the chochlear duct is the perilymph scalae are in realty one long tube, beginning at the oval window and terminating at the round window F23_20 Bez názvu 1 kopie Cochlea_azan kopie nThe cochlear duct has triangular nprofile in sagittal section n n3 walls : na vestibular membrane (Reissner´s membrane) n na lateral wall n na tympanic wall n- including the basilar nmembrane with the organ nof Corti peripherally n n- the osseous spiral lamina ncentrally Smyslové orgány II - 19 nthe vestibular membrane (Reissner´s membrane) nis very thin and covered from both sides by a simple squamous epithelium n nextensive tight njunction are nbetween cells nof both layers F23_24 F23_24 Ductus cochlearis (scala media) The lateral wall extends from the insertion of the vestibular membrane to the spiral ligament its core is a thickened periost covered by highly vascularized stratified epithelium - called as stria vascularis 3 types of cells: marginal, intermediate, and basal marginal cells are responsible for the characteristic ionic composition of endolymph Starting from the prominentia spiralis (thin-walled blood vessel - vas prominens lying here in dense connective tissue), the stria vascularis epithelium is replaced by simple cuboidal epithelium nThe tympanic wall nconsists of the basilar membrane and osseous spiral lamina n nthe membrane extends between the crista membranae basilaris and the labium tympanicum of the limbus laminae spiralis nis composed of fibrils related to keratin (are produced by cells of the organ of Corti as well as cells lining the scala tympani) nthe basilar membrane is about 100 mm wide in the basal turn of the cochlea and 500 mm in the apical turn nthe sound receptor known as organ of Corti rests on the membrane F23_24 Bez názvu 1 kopie nORGAN OF CORTI (seu papilla spiralis) n nconsists of supporting cells and hair cells n nSupporting cells n involve several different types n lie in rows arranged in direction from sulcus spiralis externus to sulcus spiralis internus: n nClaudius´ cells and Boettcher´s cells - columnar in shape and line the external spiral sulcus nHensen's cells - form several rows and are tall and slim nouter phalangeal (Deiter's) cells lie in 3 to 5 rows (depending on the position of the turn (apically the number of rows is increasing) nouter and inner pillars cells that limit the inner tunnel (of Corti), pillar cells are highly modified epithelial cells whose apices terminate with cuticular plates, their bodies contain numerous tonofilaments n the Nuel' s space - between the outer pillar cells and adjacent row of phalangeal cells ninner phalangeal cells - lie axially to the inner pillar cells and only in one row nborder cells - tall and slim cells lowering in height towards the internal spiral sulcus ninterdental cells - cover the labium vestibulare of the limbus laminae spiralis and produce gelatinous membrana tectoria or tectorial membrane extending above the apices of hair cells. n 009 nHair cells nthe outer hair cells - lie in 3 -5 rows and are supported by the outer phalangeal cells nthe inner hair cell - occur in single row and are supported by the inner phalangeal cells nhair cells are columnar, with nuclei located basally, numerous mitochondria and ncisternae of smooth endoplasmic reticulum in the cytoplasm n napices of hair cells are provided with nstereocilia n- W shaped in the outer cells and n- linear in the inner ones nthe height of stereocilia increases nfrom one side of array to the other n nthe tips of the tallest stereocilia nof the outer hair cells are embedded nin the tectorial nmembrane F23_25 Smyslové orgány II - 29 Smyslové orgány II - 27 Bez názvu 1 kopie ghanglionspirale nFunction of the organ of Corti: nbecause the ossicle form a unit and the base of stapes is inserted in the oval window, vibrations of the tympanic membrane cause the vibrations of perilymph of both scalae (vestibuli and tympani) nthe pressure changes are transmitted across the vestibular and basilar membrane of the cochlear duct, which result in positional changes of stereocilia against tectorial membrane nsequence of mentioned processes induces to arise action potentials within hair cells nOUTLINE OF DEVELOPMENT OF THE EAR n nTHE EXTERNAL EAR nThe external acoustic meatus develops from the dorsal end of the 1st branchial groove; ectodermal cells at the bottom of the groove proliferate and extend inward as a solid epithelial plate - meatal plug; in the fetal period, the central cells of this plug degenerate, forming cavity that becomes the inner part of the external acoustic meatus Smyslové orgány II - 13 nThe auricle n develops from 6 swellings known as auricle hillocks that surround the margin of the first branchial groove n 3 hillocks are on the first branchial (mandibular) arch and 3 on the second (hyoid) branchial arch n at the end of the 2nd month all hillocks fuse to form the definitive pinna Smyslové orgány II - 14 n The tympanic membrane (TM) derives from the branchial membrane separating the 1st branchial groove from the 1st pharyngeal pouch initially, the membrane is made up of only the ectoderm and endoderm, as development proceeds, mesenchyme grows between both germ layers and is differentiated into the fibrous stratum of the TM, the ectoderm gives rise to the epidermal and the endoderm to the mucous aspect of the definitive TM nTHE MIDDLE EAR n n2 different embryonic anlages - the 1st pharyngeal pouch and n- cartilages of the 1st and 2nd pharyngeal arches n nThe tympanic cavity - 1st pharyngeal pouch - its distal expanded end then envelopes the auditory ossicles n the proximal unexpanded portion becomes the Eustachian tube Smyslové orgány II - 13 nthe auditory ossicles nthe malleus and incus from dorsal part of Meckel´s cartilage (supporting the first branchial or mandibular arch) nthe stapes from dorsal part of Reichert´s cartilage (supporting the second or hyoid branchial arch) Smyslové orgány II - 15 during the late fetal period, the tympanic cavity becomes larger and expands into the temporal bone = mastoid antrum nTHE INNER EAR ndevelopes from the ectoderm n nfirst anlage occurs early during the 4th week as a thickened plate of the ectoderm n- otic placode - on each side of the head nplacode invaginates and sinks below the surface ectoderm into the underlying nmesenchyme to form otic pit nedges of the pit come together and fuse to form an otic vesicle or otocyst that lies nlaterally to the rhombencephalon n Smyslové orgány II - 7 Smyslové orgány II - 8 the otocyst serves a primordium of future membranous labyrinth two divisions are early recognizable on the otocyst: a dorsal or utricular portion, differentiating into the utricle, semicircular ducts and endolymphatic duct and sac and a ventral or saccular portion that gives rise to the saccule and cochlear duct Smyslové orgány II - 9 n nInitially, the semicircular ducts form flat-like diverticula growing out from the utricular portion; central parts of them then fuse and disappear n nthe peripheral infused portions of the diverticula become the semicircular ducts n nfrom the ventral saccular portion of the otocyst, the coiled cochlear diverticulum grows out n nstarting the 4th month, differentiation of maculae begin in the utricle and saccule, cristae within semicircular ducts and the organ of Corti within the cochlear duct n nthe mesenchyme around the otic vesicle (later its parts) condenses and differentiates into the bony labyrinth na space separating the membranous labyrinth from the osseous one soon fills the perilymph Smyslové orgány II - 10 Smyslové orgány II - 12