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

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 semicircular duct cross section

hair cells (type I and II) supporting cells

vestibular afferents and efferent fibers

It is similar to the macula, but there are no striolas or otoliths. Kinocilia are arranged in one direction. Angular acceleration and movements of the endolymph Semicircular canals are paired bilaterally right left

Vestibulo-ocular reflex (VOR)- keeps the eyes Disharmony of vestibular and visual information causes focused on target when the head moves. dizziness, nausea and vomiting (ie:. motion thickness). The central vestibular sytem

Edinger-Westfal nucleus somatosensory control: thalamus- conscious perception of parietal cortex movement and gravity fasciculus controlling eye longitudinalis movements: medialis • VOR

Vestibular nuclei Superior (Bechterew) Medial (Schwalbe) Lateral (Deiters) Inferior (Roller) tractus tractus vestibulospinalis vestibulospinalis medialis lateralis Spinal cord premotor neurons

position of the head position of the body, walking upright Cerebellar connections

Inferior cerebellar peduncle 2nd order neurons: Cerebellum Vestibular nuclei: coordinating postural adjustments (sequence of medial 4th ventricle movements) inferior direct innervation

indirect 1st order neurons innervation

vestibulo-cerebellar tract: cerebello-vestibular tract : • 1st and 2nd order neurons • n. fastigii, flocculonodular cortex • mossy fibers • vestibular nuclei • Flocculonodular lobe (vestibulocerebellum)