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The Bony and the Membranous Labyrinth

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The bony and the membranous labyrinth Zsuzsanna Tóth, PhD Semmelweis University, Department of Anatomy, Histology and Embryology The inner ear semicircular canals of bony labyrinth vestibule vestibulocochlear nerve cochlea middle ear auditory tube Location: In the petrous part of the temporal bone. Functions: Parts: • hearing (cochlea, spiral organ of Corti) • bony labyrinth • balance • membranous labyrinth • spacial orientation • ganglia and final branches of the vestibulocochlear nerve (VIII.) The bony (osseous) labyrinth vestibule semicircular canals cochlear branch of semicircular cochlea oval (vestibular) of bony labyrinth nerve VIII. canals window sagittal α frontal ∙ α ~45° α vestibular vestibulocochlear branch of nerve VIII. nerve (VIII.) round (cochlear) internal vestibule window cochlea acustic meatus promontory (base of the cochlea, medial wall of the tympanic cavity) Left osseous labyrinth, lateral view Bony limbs (crura) of semicircular canals (5): superior (vestibular connections) • 3 ampullary crura ampullary osseus crura • 1 simple crus, common crus • 1 common crus elliptical recess spherical recess apex lateral (cupula) posterior simple crus cochlea fenestra vestibuli ampullary osseus crus base fenestra cochleae Interior of the vestibule Maculae cribrosae: • superior, media, inferior, • perforated areas for entering the branches of the vestibular elliptical recess nerve: ( for the utricle) 1. utriculoampullar nerve, spherical 2. saccular nerve, recess ( for the saccule) 3. posterior ampullary nerve semicircular canals fossa orifice of the vestibular cochlearis vestibular crest aqueduct Interior of the right osseous labyrinth The cochlea I. m: modiolus: • longitudinal canals of modiolus, one bigger and several smaller channels, vessels, spiral canal of cochlea cochlar n. • spiral canal of the modiolus; spiral ganglion m scala vestibuli* m scala * tympani *: perilymph secondary spiral lamina osseous spiral lamina (at the lower part only) cochlear duct (endolymph) spiral foraminous tract- filaments of the cochlear nerve exit (fundus of the internal acustic meatus) The spiral canal stria vascularis vestibular membrane (Reissneri) scala vestibuli spiral osseous spiral spiral limbus scala media prominentia lamina cochlear duct internal spiral external sulcus spiral sulcus nerve fibers Organ of Corti basilar crest basilar membrane scala tympani spiral ligament The cochlea II. : scala vestibuli and tympani meet hamulus of the spiral lamina 23/4 turn osseous spiral lamina spiral foraminous tract spiral ganglion (bipolar neurons) 9mm The membranous labyrinth endolymphatic sac endolymphatic duct (*) anterior semicircular duct ant. semicircular canal dura mater vestibular aqueduct os temporale, helicotrema pars petrosa spherical cochlear duct recess elliptical recess spiral canal amp. cupular cecum posterior semicircular duct saccule scala vestibuli * v. amp. ductus reuniens lateral semic. duct lat. semicircular canal of Hansen scala tympani amp. post. semicircular canal cochlear canaliculus • perilymphatic duct v.: vestibule • vein of cochlear canaliculus • connection o the subarachnoid space cochlear recess ampullary limb of (shunt ) vestibular cecum utriculosaccular semicircular ducts duct ampullary osseus limb Interior of the vestibule Maculae cribrosae: • superior, media, inferior, • perforated areas for entering the elliptical recess branches of the vestibular (utricle) nerve: spherical recess 1. utriculoampullar nerve, (saccule) 2. saccular nerve, 3. posterior ampullary nerve vestibular crest cochlear recess vestibular aqueduct (end of the cochlear duct ) (endolymphatic duct) Interior of the right osseous labyrinth The membranous labyrinth-sensory epithelia, nerves, blood supply vestibular ganglion ( of Scarpa) utriculoampullar n.: superior and inferior-bipolar neurons ant. ampullar n. cristae ampullaris vestibular nerve lat. ampullar n. utricular n. vestibulocochlear nerve cochlear nerve macula utriculi macula sacculi posterior ampullary nerve vestibularis saccular nerve Blood supply: common cochlear artery basilar artery labyrinthine arteries anterior vestibular artery labyrinthine veins, v. of aqueduct of vestibule,v. of aqueduct of cochlea → inf. petrosal sinus → sigmoid sinus The internal acustic meatus facial canal (facial nerve) medial lateral area superior vestibular area facialis (utriculoampullar nerve) cochlear area transverse (falciform) cochlear nerve crest spiral foraminous inf. tract vestib. area saccular nerve foramen singulare (post. ampullary nerve) fundus of the internal acustic meatus The right internal acoustic meatus and its fundus, medial view. The posterior wall has been partially removed. The endo- and perilymph Perilymph: • fills the bony labyrinth protecting the membranous one p • is produced by the microvasculature of the periosteum • is drained by the perilymphatic duct into the e subarachnoideal space p • similar to the extracellular fluid or the CSF fenestra e vestibuli Endolymph: fenestra e rotunda • fills the membranous labyrinth, p • is produced by the stria vascularis (cochlea) and by the dark cells in semicircular duct SV. • is drained by the endolymphatic duct into the dura ST. mater venous sinuses • similar to the intracellular fluid ions: Sound waves in the perilymph, pressure equilibration: bicarbonate base of the stapes→fenestra vestibuli → scala vestibuli perilymph cloride → cochlear duct and helicotrema → scala tympani perilymph → potassium fenestra rotunda → secondary tympanic membrane sodium Special features of the endolymph are necessary for the sensory functions RMP = 0 mV [K+] = 3 mM • endolymph: very high (150mM) K+ and low (1mM) Na + content • endocochlear potential (EP): scala media is +80mV relative to scala tympany • EP is generated by the stria vascularis. • A strong driving force exists for K + to flow into the receptor (hair) cells (120mM K +, -40mV) during stimulus - depolarization. • The large driving force for K + entry contributes to extremely low threshold of auditory hair cells. • A recycling system allows returning of K + to the stria vascularis. • Energy (ATP) saving for hair cells: K + enters end exits the cell according to the concentration gradient. Stria vascularis - generation of the endocochlear potential stria vascularis ZO ZO GJ • epithelial barriers between the endo- and perilymph: potential K+ conc. 1. basal (B) and intermedier cells GJ 2. marginal (M) cells supported by tight junctions (ZO) • communication: gap junctions (GJ) between B, I cells and fibroblasts (F) in the spiral ligament • intrastrial space: an extracellular fluid compartment with a dense capillary network • endocochlear potential generation: B cells, KCNJ10 NKCC1 potasium channels-mutation: EAST syndrome • K+ ion concentration gradient generation: M cells, no further EP generation because of Cl- ion co-transport Production of the endolymph and K+ ion transport in the semicircular ducts light dark cell cell supporting cell light cell There is no potential, only concentration gradient. The vestibular system 1. Cristae ampullares : 2. Maculae staticae: • in the ampullae of semicircular ducts • in the utricle and saccule • the ridge of the crista is always • they lie in a perpendicular plane to each other perpendicular to the long axis of the duct • detect linear acceleration, tilt of the head and gravity • detect angular acceleration of the head. The structure of the macula sensory epithelium: ototih crystals protein, CaCO3 wall of the otolithic membrane gelatinous substance membranous labyrinth: glycoproteins non-sensory hair cells apical cilia, epithelium rest between the supp. cells squamous and don’t reach the l. propria cuboidal cells, dark secondary sensory cells: and light cells no own axons basal afferent nerves lamina peripheral processes of bipolar neurons in the vestibular ganglion lamina propria connective tissue, reticular lamina vessels, nerve fibers supporting cells a cuticle formed by the union of melanocytes, mechanical support and the apical surfaces of trabeculae-fixation nourishment for hair cells, supporting cells - to the bony labyrinth secretion of otolithic tight junctions membrane components Pattern of membrane potential and firing of the hair cells Resting Resting Resting impulse impulse impulse frequency frequency frequency Stereocilia: Kinocilium: • 30-300pcs/ hair cell, • 1pc/ hair cell • large microvilli, • a real cilium: 9 + 2 array • arranged by size, of microtubules • contain actin filaments, • taller then the • contain fimbrin -rigidity. stereocilia Orientation of cilia - a key of sensitivity to multiple directions striola striola (utricle) saccule kinocilium stereocilia Orientation of kinocilia: • kinocilia are oriented in opposite direction on each side of the striola • utricle - kinocilia are facing the striola • saccule- kinocilia are facing away from the striola • this arrangment allows sensing linear acceleration in every directions Signal transmission, types of hair cells Hair cell: • secondary sensory cell • basal cell nucleus, synaptic vesicles (glutamate) • ribbon synapses facing the afferents of the vestibular nerve • efferent fibers; central modulation, modulation of sensitivity Type II. hair cell: Type I. hair cell: • narrow, cylindrical, • flask shaped, • extrastriolar, • striolar, • bouton-like synapses, • calyx endings of afferent nerve, • more afferent / hair cell, • 1 afferent / hair cell, • slower signaling, • fast signaling • better signal to noise ratio The structure of the ampullary crest epithelial lining of the
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