Sense Organs [download]

Sense Organs1. Sense organs – classification2. Sensory receptors3. Gustatory apparatus4. Olfactory apparatus5. Visual apparatus – the eye. Visual pathway6. Vestibulocochlear apparatus – the ear.Auditory and vestibular pathways

four kinds of touch sensations: light toucht(contact) cold heat painSense of touchSense organsProf. Dr. Nikolai Lazarov 3

3 main groups – Sherrington, 1906: exteroceptors proprioceptors interoceptorsby sensory modality: baroreceptors – respond to pressure chemoreceptors – chemical stimuli mechanoreceptors – mechanical stress nociceptors – pain perception thermoreceptors – temperature (heat, cold or both)by location: cutaneous receptors muscle spindlesby morphology:Sensory receptors – classification free nerve endings encapsulated receptorsC.S. Sherrington1857–19521952Sense organsProf. Dr. Nikolai Lazarov 4

peripheral gustatory organs: taste buds(gustatory caliculi) – 2000-9000: vallate papillae – most numerous plentiful in the posterior ⅓ of the tongue fungiform papillae soft palate, epiglottis and pharynx no structural difference among taste buds: gustatory (taste) pore – 2-3 µm collection of 50-100 epithelial cells contain long microvilliextend through a taste pore contain two types ofgustatory receptor cells• with and without dense-cored granules supporting (non-sensory) cells basal cells – undifferentiated,form new receptor cells every 10-14 daysGustatory apparatusNB:Sense organsNB: about 50 fibers innervate a single taste bud!Prof. Dr. Nikolai Lazarov 5

traditionally four basic qualitiesof taste: sweetness bitterness sourness saltiness fifth basic taste umami (“deliciousness”) –non-salty sensations evoked by someamino acids – glutamateGustatory apparatusSense organsNB: about 50 fibers innervate a single taste bud!NB:Prof. Dr. Nikolai Lazarov 6

the sense of smell (olfaction): receptors are part of the olfactory epitheliumolfactory mucosa – 3 cell types: cell bodies of olfactory receptor cells(40 million in human olfactory epithelium)Olfactory apparatus supporting cells – columnar cells basal cells – form new receptor neurons (4-8 weeks) olfactory (Bowman’s) glands – in lamina propriaSense organsNB: The smell receptors are sensitive to seven types of sensation:NB:The smell receptors are sensitive tocamphor, musk, flower, mint, ether, acrid, or putrid!Prof. Dr. Nikolai Lazarov 7

Olfactory neuroepitheliumnon-myelinated axons of theolfactory epithelium: gather into 18-20 bundles –filaments of the olfactory nerve (CNI) pass through the cribriform plate of theethmoid bone attach to the olfactory bulbsSense organsProf. Dr. Nikolai Lazarov 8

transmits smell informationfrom the nose to the brain:Olfactory bulb supported and protected by the cribriform plate multi-layered cellular architecture: glomerular layer external plexiform layer mitral cell layer internal plexiform layer granule cell layerSense organs olfactory bulb – synaptic glomeruli: nucleus of termination of cranial nerve I mitral, granule and periglomerular cells initial part of rhinencephalonProf. Dr. Nikolai Lazarov 9

consists of: axons of the mitral and tufted cells centrifugal axons from the opposite bulbanterior olfactory nucleus: medium-sized multipolar neurons their axons continue into the olfactorystriae and trigoneolfactory striae:Olfactory tract lateral olfactory stria limen insulae medial olfactory stria diagonal band of Brocaanterior perforate substanceolfactory tubercle – reduced in manSense organsProf. Dr. Nikolai Lazarov 10

primary olfactory cortex: prepiriform cortex – lateral olfactory gyrus gyrus ambiens periamygdaloid area – lateral olfactory stria gyrus semilunaris secondary olfactory cortex: entorhinal area, cranial part of parahippocampal gyrusSense organsOlfactory cortex (piriform lobe)Prof. Dr. Nikolai Lazarov 11

The eye – some amazing facts:Human visual organs the eyeball of a human weighs approximately 28 g; g although only 1/6th of it is exposed to the outsideworld, about half of our brain is involved in the seeingprocess – humans are thus very much visual animals! the only part of our body that can function at 100%ability at any moment, day or night, without rest; most complex organs we possess – composed ofmore than 2 million working parts; the external muscles that move the eyes are thestrongest muscles in the human body for the job thatthey have to do. They are 100 times more powerfulthan they need to be! the retina contains 120 million rods for "night vision",and 8 million cones that are colour sensitive andwork best under daylight conditions; contributes towards 85% of our total knowledge –can process 36,000 bits of information every hour.NB: Human eye: a window to the outside world!NB:Human eyeProf. Dr. Nikolai Lazarov 12

The eye – Lat. oculus, , Gr. ophthalmos: eyeball – coats ocular fibrous tunic• sclera• cornea vascular tunic (uveal tract) retina• choroid• ciliary body• iris ocular refractive media aqueous chamber&humor vitreous body lens accessory structures extraocular muscles eyebrows and eyelids lacrimal apparatusAnatomy of the eye Human eyeProf. Dr. Nikolai Lazarov 13

EyeballHuman eye Eyeball – the peripheral organ of sight: embedded in the fat of the orbit enveloped by a fascial sheath (capsule of Tenon) anterior and posterior poles optic (visual) axis approximately spherical “ball” – dimensions: vertical diameter – 23.5 mm anterioposterior diameter – 24 mm (17.5 mm at birth) three coats (tunics): fibrous tunic vascular, pigmented tunic nervous layer, retina content – ocular refractive mediaProf. Dr. Nikolai Lazarov 14

Human eyeOcular fibrous tunic Sclera (tunica sclera) – Gr. skleros, , hard: the outer layer of the eyeball – “the white of the eye” the posterior five-sixthsof the connective tissue coat of the globe firm protective membrane maintains the shape of the globe smooth, provides an attachmentfor the extraocular muscle insertions perforated by many nerves and vessels lamina cribrosa, sinus venosus sclerae (canal of Schlemm) opaque with varying thickness: 1 mm at the posterior pole 0.3 mm just behind muscle insertions fibrous connective tissue – four layers: episclera stroma lamina fusca endotheliumProf. Dr. Nikolai Lazarov 15

Cornea – “kerat-“,, Gr. κέρας, , hornHuman eyeOcular fibrous tunic projecting and transparent front part of the eye refracts (together with the lens) light (~ 43 dioptres) the anterior one-sixthsof the connective tissue coat of the globe dense with varying thickness: ~1.2 mm round its periphery 0.5-0.6 mm at its centre non-vascular structure surface ectodermal origin richly innervated corneal (blink) reflex structurally – five layers: corneal epithelium anterior limiting membrane (of Bowman) substantia propria (corneal stroma) posterior limiting membrane (of Descemet) endothelium of the anterior chamberNB: The mnemonic "EBSDE"EBSDEin", read as "Ebstein"Ebstein"NB:Prof. Dr. Nikolai Lazarov can be used to remember the layers in sequence! 16can be used to remember the layers in sequence

ChoroidHuman eyeVascular tunic (uveal tract)Choroid – ⅔ of the uveal tract surface ~ 0.5 mm in humans: thin, highly vascular coat, dark brown or chocolate dense capillary plexus – provides oxygen andnourishment to the outer layers of the retina composition: suprachoroid lamina – ~ 30 µm thick choroid proper:• vascular lamina• capillary lamina (choroidocapillaris)• basal lamina (membrane of Bruch)NB:NB: uva, Lat. grapeProf. Dr. Nikolai Lazarov 17

Human eyeVascular tunic (uveal tract) Ciliary body – Lat. cilium, , eyelid: the circumferential tissue inside the eye triangular in horizontal section coated by a double layer, the ciliary epithelium superficial lamina – columnar cells deep layer – cuboidal cells with pigment granules composition: ciliary ring, orbiculus ciliaris (pars plana) – 3.5-4 mm corona ciliaris (pars plicata)• 70-80 ciliary processes aqueous humor• ciliary plicae ciliary muscle zonule of Zinn lens (suspensory ligament) functions:• meridional (muscle of Brückecke)• radial (oblique) fibers• circular (muscle of Müller) accommodation aqueous humor production glaucoma production and maintenanceof the lens zonulesProf. Dr. Nikolai Lazarov 18

Human eyeVascular tunic (uveal tract)Iris – Greek goddess of the rainbow: opaque, pigmented diaphragm two major regions: pupillary zone pupil• a sphincter muscle (sphincter(pupillae)• a set of dilator muscles (dilator(pupillae) ciliary zone ciliary body iridocorneal angle Fontana’s s spaces microscopic structure: pigmented fibrovascular tissue (stroma) pigmented epithelial cells functions: controlof the diameter and size of the pupil the amount of light reaching the retina responsible forthe “eye color"Iris eye recognitionProf. Dr. Nikolai Lazarov 19

RetinaRetina – Lat. rete, net: approx. 72% of the eyeball internal surface neuronal, light-sensitivelayer of the eyeball two principal parts – ora serrata: anterior “blind” part• ciliary part• iridial part posterior optic part• macula lutea fovea centralis• optic disc – “blind spot” structure – two major layers: outer stratum pigmentosum pigment epithelium inner stratum nervosum functions: the same function as the film in a camera• receives the image seen through our eye• converts a light signal into a neural signal("signal transduction")• transmits this image through the optical nerveto the brainHuman eyeProf. Dr. Nikolai Lazarov 20

three layers of retinal neurons two layers of synapses retinal pigment epitheliumHuman eyeStructure of the retina 4-66 million hexagonal cells – fuscin5 cell types: neuroepithelial (photoreceptor) cells– in stratum neuroepithelialerodscones bipolar cells– in stratum ganglionare retinae ganglion cells– in stratum ganglionare nervi optici horizontal cells – GABAergic interneurons– in stratum plexiforme externum amacrine cells– in stratum plexiforme internum neural part of retina – 5 cell typesProf. Dr. Nikolai Lazarov 21

Photoreceptor cells neurons capable of phototransduction classic photoreceptors – two main classes: rods – 75 to 150 millionadapted for low light "night vision“contain rhodopsin cones – ~ 7 millionfunction well in bright light “daylight”detect colors – three different types• responding to short (blue) light• responding to medium (green) light• responding to long (yellow-red) light photosensitive ganglion cells –1-2% of all (1.3 million) ganglion cells in humans the same basic structure: cell body with nucleus in outer nuclear layer outer segment (discs), stalk (cilium), inner segment(mitochondria) in photoreceptor layerHuman eyeProf. Dr. Nikolai Lazarov 22

Bipolar cellsHuman eyetransmit signals from the photoreceptors to the ganglion cells – interneurons three types bipolar neurons: rod bipolar cells midget (cone) cells flat bipolar cells common bipolar cell structure: a central cell body in inner nuclear layer outer process makes synapse with either rods or cones inner process accepts synapses from horizontal cellsdirect innervation of the photoreceptor above it,either through ametabotropic (ON)or ionotropic (OFF)receptorProf. Dr. Nikolai Lazarov 23

Ganglion cellsreceive visual information from photoreceptorsvia bipolar and amacrine cellstransmit visual information from retina to several regions in brain~ 1.2 to 1.5 million retinal ganglion cells in the human retina five main classes of ganglion neurons: midget ganglion cells – monosynaptic; A cells parasol (magnocellular;(B cells) polysynaptic (rod and flat) ganglion cells photosensitive ganglion cells structure: a central cell body in ganglionic cell layer inner process makes synapse with either bipolar or amacrine cells outer process – long axon extending into the brain forms the optic nerveHuman eyeProf. Dr. Nikolai Lazarov 24

macula lutea (Lat.Macular areaLat.macula, , "spot" + lutea, , "yellow"): oval-shaped highly pigmented yellow spotwith diameter of around 5 mm centre of the macula is the foveal pit, fovea the fovea contains the largest concentration ofcones in the eye allows for the sharpest vision optic disk (papilla):fovea centralis location where ganglion cell axons exit the eyeto form the optic nerve placed 3 to 4 mm to the nasal side of the fovea vertical oval with a central depression, optic cup contains no light sensitive receptor cells –“the blind spot”Human eyeProf. Dr. Nikolai Lazarov 25

Inverted retina ‘inverted’ arrangement of the vertebrate retina: the light sensing cells sit at the back sideof the retina light has to pass through severalinner layers of its neural apparatusbefore reaching the photoreceptors an n image of the external environmentis thus focused on the retina whichtransduces light into neural signals neural impulses pass back fromthe photoreceptor layer throughthe ganlionic cell layer to the optic nerve opposite directions of lightand nerve impulse!Human eyeProf. Dr. Nikolai Lazarov 26

Ocular refractive media: aqueous chambers –anterior and posterioraqueous humor vitreous chambervitreous body lensHuman eyeOcular refractive mediaProf. Dr. Nikolai Lazarov 27

Human eyeAqueous chambers and humor aqueous chambers: anterioranterior – between the posteriorsurface of the cornea and the iris posterior – between the iris andthe front face of the vitreous body aqueous humor: provides nutrients to the lensand corneal endothelium maintains the convex shape of the cornea carries away waste products from metabolism composition: water – 99%, glucose, amino acids ions: HCO - 3 ; Cl - ; Na + ; K + ; Ca 2+ ; PO 3-4 proteins: albumin, β-globulins production and drainage: secreted into posterior chamber by the ciliary body drains into Schlemm’s canal glaucomaProf. Dr. Nikolai Lazarov 28

Human eyeVitreous chamber and body vitreous chamber – ~4/5 of the eyeball the gel in vitreous chamber is stagnant vitreous body: transparent, colourless, gelatinous mass produced by certain retinal cells structure: vitreous (hyaloid) membrane peripherally hyaloid canal centrally very few cells – phagocytes and hyalocytes contains no blood vessels composition: water – 99% some salts little glycoprotein and hyaluronate vitrosin (a type of collagen) functions: refracting media helps to keep the retina in placeProf. Dr. Nikolai Lazarov 29

lens: transparent, biconvex body structure: anterior and posterior poles equator and capsule soft cortical substance firm, central part, nucleus contains no true elastic tissue lens fibers (cells) – superficial and deep function:Lens helps to refract light to be focused on the retina contributes about 15-18 dioptres (⅓)to the total dioptric powerHuman eyeProf. Dr. Nikolai Lazarov 30

Extraocular muscles Eyebrows and eyelids Conjunctiva Lacrimal apparatusHuman eyeAccessory visual apparatusProf. Dr. Nikolai Lazarov 31

extraocular muscles: elevator of the upper eyelid superior and inferior tarsal muscles orbital muscle four recti muscles – annular tendon superior rectus inferior rectus lateral rectus medial rectus two obliqui muscles obliquus superior obliquus inferiorHuman eyeExtraocular musclesProf. Dr. Nikolai Lazarov 32

Eyebrows eyebrows: two arched eminences of skin numerous short, thick hairs fibers of orbicularis oculi, corrugator and frontalbelly of occipitofrontalis muscles functions: protect the eye – prevent moisture, mostly saltysweat and rain, from flowing into the eye important to human communication and facialexpressionHuman eyeProf. Dr. Nikolai Lazarov 33

eyelids, palpebrae: thin, movable foldsthat covers and protects eyesEyelids upper eylid is larger and more movable palpebral fissure lateral angle of the eye (lateral canthus) medial angle (medial canthus) lacus lacrimalis lacrimal caruncle – small, reddish, conical body lacrimal papilla punctum lacrimale eyelashes – short, thick curved hairs ciliary glands (of Moll) Meibomian (tarsal) glandsHuman eyeProf. Dr. Nikolai Lazarov 34

conjunctiva: transparent mucous membrane consisting of cells and underlyingbasement membrane over the inner surface of the eyelidsConjunctiva over the front part of the sclera and cornea palpebral conjunctiva highly vascular adherent to the tarsi conjunctival fornix ocular conjunctiva thin, transparent loosely connected to the eyelid continues as the corneal epithelium semilunar fold of conjunctivaHuman eyeProf. Dr. Nikolai Lazarov 35

lacrimal gland lacrimal canaliculi lacrimal sac nasolacrimal (tear) ductHuman eyeHuman lacrimal apparatusProf. Dr. Nikolai Lazarov 36

Lacrimal glandHuman eyealmond-like, two parts by the aponeurosisof the levator palpebrae superioris muscle: larger upper orbital part – in fossa lacrimalis smaller lower palpebral part, ⅓ of the orbital small accessory lacrimal glands more numerous in the upper lid in and near the conjunctival fornices ~12 ducts into the superior conjunctival fornix secretes a complex fluid, the tearsProf. Dr. Nikolai Lazarov 37

Lacrimal pathways lacrimal canaliculi – superior and inferiorsuperior and inferior: ~10 mm in length dilated into ampullae commence at the puncta lacrimalia lacrimal sac: upper blind end of the nasolacrimal duct connect it with the lacrimal canaliculi ~12 mm in length, lodged in a fossa nasolacrimal (tear) duct: membranous canal; ~18 mm long drains into the inferior nasal meatusHuman eyeStructure of the tear filmObstruction of the lacrimal drainageProf. Dr. Nikolai Lazarov 38

Prof. Dr. Nikolai Lazarov 39

The peripheral auditory apparatus, the ear,auris, Gr. us, ωτο = genitive for ear: external (outer) ear, auris externa auricle (pinna) external auditory meatus (ear canal) middle ear, auris media tympanic membrane (ear drum) tympanic cavity auditory (Eustachian) tube auditory ossicles internal (inner) ear, auris internaauditory and vestibular portions: osseous labyrinth membranous labyrinthAnatomy of the earNB:Human earNB: Human ear: the organ of hearing and balanceProf. Dr. Nikolai Lazarov 40

External ear, auris externa the first structure of the sound conduction apparatus – serves tocollect and conduct the air vibrationsto the tympanic membraneHuman earauricula auricle (pinna) – auricula external acoustic meatus(ear canal)– meatus acusticusexternusProf. Dr. Nikolai Lazarov 41

pinna – Lat.Lat. pinna, , a feather: thin skin with fine hairs elastic fibrocartilage lobule of auricle auricular tubercle(of Darwin) ligaments of auricle,extrinsic and intrinsic, auricular muscles –extrinsic and intrinsic,n. facialisAuricle, auriculaHuman ear collects and funnels the sound wavescollects and funnels the sound wavesinto the meatusProf. Dr. Nikolai Lazarov 42

External acoustic meatus,meatus acusticus externusexternal auditory meatus (earcanal),Lat. meo, , a passage length ~ 2.5 cm; 7 mm in diameter S-shaped curve (140°)structure – two parts: cartilaginous part – outer ⅓ (~8 mm long),cartilago meatus acustici osseous part – inner ⅔ (~16 mm long),meatus acusticus externus thin skin; the thicker cerumen-producing ear canalskin has fine hairs, tragi sebaceous glands in the hair follicles ceruminous glands ear wax, cerumenHuman ear conducts the sound waves to the ear drumNB: The ear wax assists in cleaning and lubrication, and alsoProf. Dr. Nikolai Lazarov provides some protection from bacteria, fungi, , and insects!43

a structure of the sound conduction apparatusprimary functions: transmission of the vibrations of thetympanic membrane to the internal ear efficient transfer of acoustic energyfrom compression waves in air to fluid –membrane waves within the cochlea tympanic membrane –membrana tympani (tympanica) tympanic cavity –cavitas (cavum) tympani auditory (eustachian) tube –tuba auditiva(auditoria) auditory ossicles –ossicula auditus(auditoria)Middle ear, auris mediaHuman earProf. Dr. Nikolai Lazarov 44

ear drum – thin, semi longest diameter d=10-11 mm shortest diameter d=8-9 mm pars flaccida –Schrapnell’s membrane pars tensa umbo cuticular layer fibrous layer –absent in pars flaccida: radiate fibers circular fibers mucous layersemi-transparent, nearly oval in form:Human earTympanic membrane, membrana tympaniProf. Dr. Nikolai Lazarov 45

volume – 1.5 cm 3 , air-filleddiameters: vertical – 15 mm transverse – 6-4-2 mm antero-posterior – 15 mmtwo parts: tympanic cavity proper epitympanic recessHuman earTympanic cavity, cavum tympanithree clinically important levels: epitympanum mesotympanum hypotympanumProf. Dr. Nikolai Lazarov 46

Eustachian (pharyngotympanic(pharyngotympanic) ) tube,links the pharynx to the middle ear, ~3.5 cm long: ostium tympanicum tubae ostium pharyngeum }auditivaetwo parts: cartilaginous part - ⅔ (cartilago tubae auditivae) – 24 mm bony part - ⅓ (in semicanalis tubae auditivae) – 12 mm isthmus tubae auditivae mucous membrane – ciliated columnar epitheliumHuman earAuditory tube, tuba auditivaProf. Dr. Nikolai Lazarov 47

Human earAuditory ossicles, ossicula auditusmalleus – Lat. = mallet, hammer; the largest, 8-9 mm long: head, caput mallei neck, collum mallei handle, manubrium mallei anterior and lateral processesincus – Lat. = anvil: body, corpus incudis longprocess, crus longum lenticular process short process, crus brevestapes – Lat. = stirrup: head, caput stapedis limbs (crura) anterius posterius base, basis stapedism. tensor tympani (Eustachii)m. stapediusligg. et artt. ossiculorum auditusProf. Dr. Nikolai Lazarov 48

Internal ear, auris internalocation – in pars petrosa ossis temporalismain functions: converts sound waves into nerve impulses registers changes in equilibriumcomposition: osseous labyrinth,labyrinthus osseus membranous labyrinth,labyrinthus membranaceusHuman earProf. Dr. Nikolai Lazarov 49

vestibule, vestibulum three semicircular canals,canales semicirculares: canalis semicircularis lateralis canalis semicircularis anterior canalis semicircularis posterior cochlea filled with perilymphHuman earOsseous labyrinth, labyrinthus osseusProf. Dr. Nikolai Lazarov 50

lateral wall –paries labyrinthicus: fenestra vestibuli closed by basis stapedis,fixed with lig. annulare stapedis fenestra cochleae membrana tympani secundariamedial wall: elliptical recess utriculus vestibular crest aqueduct of the vestibule spheroid recess sacculus cochlear recess maculae cribrosae pars vestibularisn. vestibulocochlearis: macula cribrosa superior macula cribrosa media macula cribrosa inferiorVestibule, vestibulumHuman earProf. Dr. Nikolai Lazarov 51

lateral semicircular canal (14 mm) – directed horizontally anterior (superior) semicircular canal (18 mm) – vertical posterior semicircular canal (22 mm) – directed sagittally backwards ⅔ of a circle diameter = all ~ 1 mm located in threeperpendicular planes filled with semicircular ducts initial portion – ampulla ossea end part – crus osseum: simplex – for lateral canal commune – for anterior&posterior canalsHuman earSemicircular canals, canales semicircularesvertical in directionProf. Dr. Nikolai Lazarov 52

Osseous cochlea spiral canal, canalis spiralis cochleae –2½-2¾ turns (length ~ 3 cm): height – 4-5 mm base – 8-9 mm basis cochleae cupula cochleae structure:modiolus – Lat. the hub of a wheel: basis modioli tractus spiralis foraminosus lamina modioli canalis spiralis modioli ganglion cochlearelamina spiralis ossea hamulushelicotrema membrana basilarislamina spiralis secundaria Human earLat. cochlea, , snail shellProf. Dr. Nikolai Lazarov 53

Cochlear canal, canalis cochlearisscala vestibuliLat.scala tympaniscala media (ductus cochlearis) organum spirale CortiLat. scala, , stairwayHuman earProf. Dr. Nikolai Lazarov 54

a closed system of fluid-filled membranouschannels (sacs) of ectodermal origin location – within the bony labyrinth filled with endolymph surrounded by perilymph –perilymphatic space labyrinthus vestibularis – within the osseous vestibule –utriculus and sacculus endolymphatic duct and sac three semicircular ducts labyrinthus cochlearis – membranous cochlea(cochlear duct) spiral organ of CortiHuman earMembranous labyrinth, labyrinthus membranaceusProf. Dr. Nikolai Lazarov 55

Human earVestibular labyrinth, labyrinthus vestibularis utriculus – in recessus ellipticus: ductus utriculosaccularis macula utriculi – ⅔ mm: parsutricularis n. vestibulocochlearis sacculus – in recessus sphericus: ductus reuniens ductus cochlearis macula sacculi – pars saccularisn. vestibulocochlearis ductus endolymphaticus saccus endolymphaticusProf. Dr. Nikolai Lazarov 56

semicircular ducts: ductus semicircularis lateralis ductus semicircularis anterior ductus semicircularis posterior ¼ of the semicircular canals ampulla membranacea crus membranaceus: simplex – for lateral duct commune – anterior&posterior ducts wall – thickened, three layers: inner – simple squamous epithelium middle – vascular connective tissue outer – fibrous tissue with blood vesselsclothed by flattened perilymphatic cellsHuman earVestibular labyrinth, labyrinthus vestibularisProf. Dr. Nikolai Lazarov 57

Statoreceptor spots:Vestibular system macula utriculi and macula sacculi:• neuroepithelium: epitheliocyti sensorii pilosi – 2 types 40-80 stereocilia; 1 kinocilium epitheliocyti sustentantes• membrana statoconiorum –otoliths, statoconia(Gr. oto-, ear + λιθος, lithos, a stone) cristae ampullares:• neuroepithelium: epitheliocyti sensorii pilosi – type I and II epitheliocyti sustentantes• cupula – a glycoprotein substanceHuman earProf. Dr. Nikolai Lazarov 58

Human earCochlear labyrinth, labyrinthus cochlearis cochlear duct,ductus cochlearis: scala media –endolymph length ~35 mm cecum vestibulare –in recessus cochlearis cecum cupulae –in cupula cochleaeProf. Dr. Nikolai Lazarov 59

Cochlear duct, ductus cochlearis paries vestibularis – vestibular membrane(of Reissner) – two layers: basal lamina simple squamous epithelium paries externus: lig. spirale cochleae stria vascularis: three cell types:marginal, intermediate and basal – secrete endolymph paries tympanicus – basilar membrane(membrana spiralis): internal zone – sulcus spiralis internus,limbus spiralis (tympanic and vestibular lips membrana tectoria), middle zone – spiral organ of Corti external zone – sulcus spiralis externusHuman earProf. Dr. Nikolai Lazarov 60

Spiral organ of Corti, organum spiraleAlfonso Corti(1822–1876)Human ear located onto basilar membrane: 100 µm basal, 500 µm apical turnsreceptor (sensory) and supporting cells: internal and external rod (pillar) cells of Corti cuniculus internus (inner(tunnel of Corti) cuniculus medius (space(of Nuel) internal phalangeal cells of Deiters – 1 row andexternal phalangeal cells of Deiters – 3 rows internal (inner) hair cells – 1 row andexternal (outer) hair cells – 3 rows cuniculus externus (outer(tunnel) epitheliocyti limitantes externi(cells of Hensen) – 3-4 rows epitheliocyti sustentantes externi(cells of Claudius) supporting cells of Boettcher – beneathClaudius cells in the lower turn of the cochlea epitheliocyti limitantes interni – 1-2 rows epitheliocyti sustentantes interni – 2-3 rowsProf. Dr. Nikolai Lazarov 61

Tectorial membrane,membrana tectoria (Cortii)Human earoverlies the sulcus spiralis internus and the spiral organ of Cortisecreted by the epithelial cells of thevestibular lip of the limbus laminae spiraliscolorless fibers embedded in a jelly-like matrix: 4 mm filaments of soft keratin glycosaminoglycanscovers the hair cells in organ of Corti,making contacts with their stereociliathe vibrating mechanism in the cochleaProf. Dr. Nikolai Lazarov 62

Human earMechanism of the auditory receptionGeorg von BékésyB(1899-1972) Helmholtz resonance theory Rutherford telephone theoryThe Nobel Prizein Physiology or Medicine 1961"for his discoveries of the physicalmechanism of stimulation within the cochlea"travelling wave theory of Békésy: basilar-membrane "resonance"NB: The human ear can nominally hear sounds in the range 12 Hzto 20,000 Hz, , with intensity levels from 0 to 20 dB!Prof. Dr. Nikolai Lazarov 63

Auditory pathwaysHuman ear I st neuron –spiral ganglion: true bipolar neurons –30000-3300033000 cells cell bodies in the spiralstructure of the cochlea peripheral processes spiral organ of Corti central processes cochlear part of thevestibulocochlear nerve II nd neuron –cochlear nuclei: dorsal cochlear nucleus ventral cochlear nucleus} lateral lemniscusProf. Dr. Nikolai Lazarov 64

Central auditory pathways III rd neuron – nucleus colliculi inferioris IV th neuron – medial geniculate nucleus acoustic radiation primary auditorycortex (A-I) = Brodmann’s area 41(upper part of gyrus temporalis superior)Human earProf. Dr. Nikolai Lazarov 65

I st neuron –vestibular ganglion (ofScarpa): situated in the upper part of the outerend of the internal auditory meatus true bipolar neurons –~20000cells peripheral processes statoreceptor spots in:• maculae utriculi et sacculi –linear acceleration• semicircular ducts –angular acceleration central processes vestibular part of thevestibulocochlear nerve II nd neuron – vestibular nuclei: superior (Bechterew) inferior (Roller) medial (Schwalbe) lateral (Deiters)Vestibular pathways} lateral lemniscus tractus spinocerebellaris posteriorHuman earProf. Dr. Nikolai Lazarov 66

tractus vestibulothalamicus – nucleus ventralis posterolateralis nucleus ventralis posterior inferior tractus thalamocorticalis –internal capsule vestibular area ingyrus postcentralis (area 3a)and around sulcus intraparietalisHuman earCentral vestibular pathways III rd neuron – medial geniculate nucleus IV th neuron – vestibular cortex rostral part ofgyrus temporalis superiorProf. Dr. Nikolai Lazarov 67

Thank you…Prof. Dr. Nikolai Lazarov 68