Microscopic structure of the sense organs Aleš Hampl Sense system It serves to convey stimuli that influence organism from inside and outside Sensitive nerve endings (with simple structure) • Simple sensory endings • Intraepithelial sensory endings • Sensory bodies Complex organs • Photosensitive organ - Eye • Organ of hearing and equilibrium - Ear Photoreceptor organ – Eye Analyzes the form, light intenzity and colour reflected from objects Eye ball (three-layered structure) • tunica externa = fibrosa • tunica media = vasculosa • tunica interna = nervosa Accessory structures • eye lids • conjunctiva • lacrimal apparatus • muscles What do we expect form the eye ? • Ability to sense signals and transfer them to CNS • • Ability to focus on objects • • Enough strength • • Ability to regenerate • • Ability to move with a minimal friction • Enough strength Eyes sit in the protective environment of the skull, in orbits, surrounded by the fat cussions.. Sclera Cornea Cornea + Sclera = Tunica externa oculi 1/6 + 5/6 = 6/6 of the surface Limbus = corneoscleral junction • average thickness 0.5 mm (thicker in posterior part) • bundles of flat collagen I fibers (intesrsecting in all directions) • few fibroblasts, minimum ground substance • relatively avascular • connected by loose system of collagen fibers with Tenon´s capsule - Tenon´s space – allows for free movement of the yee • lamina suprachoroidea – connection to choroid (loose connective tissue with melanocytes, fibroblasts and elastic fibers) Sclera Cornea • average thickness 0.9-1.0 mm • colorless • transparent • thoroughly avascular • 5 distinct layers continues on the next slide Sulcus clerae • stratified + squamous (5-6 layers) • nonkeratizing • rich in nerve endings • surface cells equipped with microvili (protrude into the space with the film of tears) = Lamina limitans anterior • thickness about 7 – 12 mm • fine collagen fibers (intersecting in all directions) • no cells • provides strength = Lamina limitans posterior • fine collagen fibers • fibers are arganized to 3D network Cornea (transversal section) Corneal epithelium Bowman´s membrane Substancia propria corneae = STROMA Descemet´s membrane Corneal endothelium • many layers of collagen fibers (in right angles) • flat keratocytes in between the collagen lamellae (fibroblast-like cells) • contains mucoid substance rich in chondroitinsulphate • properly hydrated • simple + squamous • active in transport to maintain cornea in a proper state • continues on the frontal part of iris (via spongium anguli iridocornealis) KEY to the TRANSPARENCY Ability to regenerate Limbus – corneoscleral junction Sclera Cornea Limbus Limbus The area of transition of the transparent collagen bundles of cornea into the opaque collagen bundles of sclera. Highly vascularized – feeds avascular cornea Stroma Epithelium Vessels Limbus Cornea p63 p63 SC Choroid + Ciliary body + Iris = Tunica media Choroidea Corpus ciliare Iris T. vasculosa Choroid Iris Ciliary body Enough supply of resources Choroid Lamina suprachoroidea • loose connective tissue • rich for pigment cells - melanocytes Lamina vasculosa • loose connective tissue • rich for pigment cells - melanocytes • contains larger vessels and nerves Lamina choriocapillaris • loose connective tissue • network of small vessels Lamina vitrea = L. basalis = Bruch’s membrane • fibers of collagenu a elastin • averall thickness about 3-4 mm • links together basal lamina s of Lamina choriocapillaris of choroid and pigmented epithelium of retina Choroid = 4-layered structure Ability to focus on objects Ciliary body – anterior extension of the choroid Triangular on crossection Connects to: • lens + posterior chamber (A) • sclera (B) • vitreous body (C) • CB B C A Processes of CB (Processus ciliares) • protrude into posterir chamber • total number of about 70-80 • rich for capilaries (chamber fluid) • covered by two-layered epithelium (from the retina – pars ciliaris retinae) • linked to the lens capsula fibrae suspensoriae lentis (zonulae) Stroma of ciliary body • loose connective tissue • contains elastic fibers, vessels and melanocytes • rich for capillaries (chamber fluid) • bundles of smooth muscle fibers (anchored to sclera and protrude to the processes of ciliary body – m. ciliaris) Choroid Iris Ciliary body Ciliary body Zonulae CB processes M. ciliaris Closer sight Longer sight • muscle contracted • zonulae loosened • muscle relaxed • zonulae stretched Lens accommodation Stroma Ciliary body Lens Iris - 1 Anterior continuation of the choroid. Partially covers the lens. Iris Iris Pupil Lens Anterior epithelium • continuation of the posterior ep. of the cornea • discontinuos layer of flat epithelial cells, fibroblasts a melanocytes Anterior border layer • thin layer of connective tissue • rich for pigmented cells - melanocytes • decides about eye colour Stroma • loose connective tissue • large number of radially running vessels • concentrically ordered smooth muscle fibers (=musculus sphincter pupillae) Pars iridica retinae • 2-layered • continues form ciliar body • layer facing the stroma contains smooth muscle fibers (=musculus dilatator pupillae) Iris = 4-layered structure Layers from outside: 1. 2. 3. 4. Iris - 2 iris 2 M. dilatator pupilae Stroma Pigmented epithelium M. sphincter pupilae Epithelium + border layer Posterior chamber Lens Lens Epithelium (cuboidal + low cylindrical) only on the anterior surface. Fibrae suspensorie lentis are anchored to the equator of the lens. Epithelium Lens fibers Nuclei TEM Capsule + Epithelium + Fibers • 10-20 mm • Collagen IV Ability to sense signals and transfer them to CNS for processing Retina = Tunica aculi interna – Tunica nervosa Posterior part • photosensitive • multilayered Anterior part • non-photosensitive • two-layered • covers ciliary body and posterior part of the iris Invagination of prosencephalon creates two-layered optic cup. Inner layer Neural retina Outer layer Stratum pigmenti retinae • columnar cells • basally located nucleus • firm connection with lamina vitrea/basalis of choroid • zonulae occludentes and adherentes • rich for smooth ER (esterification of vit A) • rich for melanin granula • apical extensions (microvili and sheets) • vesicles in apical parts Choroid ~ 0.2 mm Neural (optical) retina minimum 15 different types of neurons with tens of interactions (synapses) Stratum pigmenti External nuclear layer External plexiform layer Internal nuclear layer Internal plexiform layer Ganglion cell layer Layer of nerve fibers Layer of rods and cones External limiting membrane Internal limiting membrane Photoreceptors = Rod and cone cells 1 I. Neurones of the optical path Stratum pigmenti External nuclear layer External plexiform layer Internal nuclear layer Internal plexiform layer Ganglion cell layer Layer of nerve fibers Layer of rods and cones External limiting membrane Internal limiting membrane External nuclear layer Layer of rods and cones Membrana limitans externa External plexiform layer (series of junctional complexes between photoreceptors and glial Muller cells) Outer segment Inner segment Central part Peripheral part Rod cells: 100-150 mil. Cone cells: 7 mil. (méně citlivé) Synaptic region Nuclear region SEM Photoreceptors = Rod and cone cells 2 I. Neurones of the optical path Other neurons of the optical path 1 Stratum pigmenti External nuclear layer External plexiform layer Internal nuclear layer Internal plexiform layer Ganglion cell layer Layer of nerve fibers Layer of rods and cones External limiting membrane Internal limiting membrane III. neuron Ganglion cells (multipolar) • Large cells • Nuclei mainly in one layer • Dendrites connect to neurites of bipolar and amakrine cells • Neurites run in 9. layer of the retina and come together to form optic nerve II. neuron Bipolar cells Diffuse • Synapses with two or more receptors Monosynaptic • Synapses with only one receptor • Direct transfer of impulses from some rods Asociating + integrating neurons Horizontal cells • Small • Multipolar • Amacrine cells • They don´t have neurite Cells with their nuclei in internal nuclear layer Other neurons of the optical path 2 Supporting cells of the retina 1 Stratum pigmenti External nuclear layer External plexiform layer Internal nuclear layer Internal plexiform layer Ganglion cell layer Layer of nerve fibers Layer of rods and cones External limiting membrane Internal limiting membrane = modified glial cells of the CNS Internal limiting membrane External limiting membrane Internal nuclear layer Supporting cells of the retina 1 Muller cells Fovea centralis of the macula lutea = the sharpest vision Papilla of the optic nerve Light Macula lutea Choroid Retina Central x Peripheral vision „Does the retina see the same in all its areas“ Audioreceptor system = Vestibulocochlear apparatus Sensing and transfer of sound Sensing static equilibrium Sensing dynamic equilibrium External ear Middle ear Internal ear Internal ear Internal ear External + Middle ear – Organ of hearing Middle ear – fitted in the cavities of temporal bone along with internal ear – osseous labyrinth. Tympanic membrane Round window Auditory meatus Maleus Stapes Oval window Incus Auricle Auditory tube (Eustachian) • Pars ossea: 2-layered vilous cylindrical epithelium • Pars cartilaginea: – multilayered -“- • Stratum mucosum • Stratum fibrosum • Stratum cutaneum • Pars ossea • Pars cartilaginea Elastic cartilage Internal ear Bony labyrinth • series of cavities • petrous portion of temporal bone Vestibulum Semicircular canals Cochlea Membranous labyrinth • series of interconnected tubes and vesicles • lined by epithelium • positioned in bony lybrinth Utricle Cochlear duct Semicircular ducts Saccule Internal ear – Organ of hearing Ductus cochlearis (Scala media) Cochlear and vestibular branches of n. vestibulocochlearis (VIII) Round window Stapes at oval window Semicircular ducts Ductus vestibularis Modiolus (bony core) • central axis of cochlear duct • contains ganglion spirale cochleae, nervus cochlearis and vessels Cochlea • 2,5 turns around modiolus • total length about 35 mm Scala vestibuli Scala tympani Cochlear branch of n.v. Scala media Vestibular membrane Ganglion spirale Tectorial membrane Basilar membrane 7 – 9 mm Helicotrema Internal ear – Detail of cochlear duct Scala vestibuli Scala tympani Scala media Bony lamina spiralis Vestibular membrane (Reissner´s) Tectorial membrane Basilar membrane Stria vascularis Stria vascularis • vascularized epithelia • responsible for the composition of endolymph? Basilar membrane • between lig. spirale and bony lamina spiralis • supports the cells of organ of Corti • made of fibrils of keratin-like proteins Ligamentum spirale PERILYMPH PERILYMPH ENDOLYMPH Tectorial membrane • product of the cells of spiral limbus • rich for glycoproteins • přes vrcholky smyslových buněk organ of Corti Internal ear – Organ of Corti - 1 Supporting cells Hensen´s cells Outer phalangeal cells • support to hair cells, which run through the spaces between ph. Outer pillar of Corti Outer pillar of Corti Inner phalangeal cells • same as inner ph. cells Border cells Secondary receptor cells • hearing hairs – stereocilia • in contact with tectorial membrane • bases wraped by dendrites of bipolar cells of ganglion spirale Outer hair cells • 3-5 rows, ~12 000, no axonema Inner hair cells • 1 row, ~3 500, no axon. Outer Inner Outer phalangeal c. Outer pillar Inner pillar Hensen´s c. Inner phalangeal c. Outer h.c. Inner h.c. Inner tunnel Tectorial membrane Basilar membrane Internal ear – Organ of Corti - 2 Inner ear – Principle of hearing Outer ear Middle ear Inner ear Middle ear ossicles Round window Oval window Auditory tube Basilar membrane 16 000 Hz 6 000 Hz 1 000 Hz Inner ear – Statokinetic / Vestibular organ - 1 Uniform composition of the wall (vessicles and tubes) Thin layer of connective tissue + single-layer squamous/cuboidal epithelium. Unifying concept of the composition of sensing elements (vessicles – maculae; tubes – cristae ampullares) Thickening of the wall with neuroepithelial cells inervated by branches of n. vestibularis. Periosteum Wall of the tube/vessicle Fibers of n. vestibularis in connective basis of macula Otoliths CaCO3 Sensing of static equilibrium (maculae = static spots) Supporting cells Hair cells Dendrites of cells gangl. n. vestibuli Otoliths Otolith membrane 25-100 mm Supporting cell Stereocilia (microvili) Kinocilium (no axonema) Hair cells Terminal plexus of tonofibrils Afferent innervation Efferent innervation Deviation from the gravity force (gravity force of otoliths) max. pressure – max. pull Position of maculae Saccule bottom Utricle lateral wall Inner ear – Statokinetic / Vestibular organ - 2 Sensing of dynamic equilibrium (cristae ampulares) Reaction on acceleration/deceleration (movement of endolymph) Position of cristae amplulares • in ampules of semicircular ducts • ridges perpendicular to axis of SDs Supporting cells Hair cells Dendrites of cells gangl. n. vestibuli Hair cells Cupula Crista Cupula Ampula bone Hair cells Inner ear – Statokinetic / Vestibular organ - 3 Development of sense organs – Overall picture Sense organs – Reminder – Neural tube Sense organs – Reminder – Neural crest Arise from both dorsal epidermis and neural plate Sense organs – Cranial neural tube + Placodes Brain after 4 weeks of development ch13_33.jpg 00002FDA Macintosh HD ABA78158: Placodes: patches of dense culumnar epithelium in the epidermis covering the head – their formation is induced by underlying brain and mesenchymal tissue – develop in week 4 Dorsolateral placodes Contribute to: •eye – lens placode •ear – otic placode •nose – nasal placode •sensory ganglia Epibranchial placodes Develop into: •sensory ganglia of cranial nerves (V, VII, IX, X) Brain after 5 weeks of development Sense organs – Eye development 1 Neural plate ectoderm -> prosencephalon (forebrain) eye fields -> -> neural plate growth carries eye field region forward -> -> eye field invaginates forming optic grooves (sulci) Sense organs – Eye development 2 Lens placode: the ectoderm invaginates in response to signals from the optic cup underneath. It then pinches off as a lens vesicle. Cells elongate to fill the vesicle and start to synthesize crystallins. Optic cup: forms from the neural tube by invagination. The opening (choroid fissure) closes forming a round optic cup, an extension of the brain. Optic stalk: connection to the brain that is filled with neurons to form the optic nerve. Reciprocal interaction: the lens induces the formation of the optic cup and the cup regulates formation of the lens. Prosencephalon – transversal section – about 30 days Epidermal ectoderm Neuroectoderm Mesenchyme Optic cup Optic vesicle Lens placode Intraretinal space Optic stalk cavity Diencephalon – transversal section – 6 weeks Neuroectoderm Lens vesicle Hyaloid artery and vein Sense organs – Eye development 3 Lumen of optic stalk Intraretinal space About 7 weeks Undifferentiated mesenchyme Optic nerve Lens epithelium Eyelid Hyaloid artery Pigmented and neural retina • m. ciliaris • proc. ciliares • stroma iridis • choroid • sclera • vitreous Histogenesis of retina ends in 8 month. Sense organs – Eye development 4 Sense organs – Ear development Rhombencephalon – transversal section Epidermal ectoderm Mesenchyme Otic placode Otic vesicle Ganglion vestibulocochleare (neural crest) Otic pit Otic pit 22 days 24 days 26 days 30 days Otic vesicle • saccular part • utricular part Thank you for your attention !