Biknevicius CPC website biknevicius/teaching.htmhttp:// biknevicius/teaching.htm Content: –Updated lectures –GRA Lab QOD & Clinical Themes

Cochlear & Vestibular Histology Audrone R. Biknevicius, PhD Ohio University College of Osteopathic Medicine CPC2 – Fall quarter 2005

HarperCollins College Publishers, 1993 Ear External ear Middle ear Inner ear Innervation: CN V3, VII, X, C2-C3 CN IX CN V3, VII CN VIII Modality: General sensations Motor to skeletal mm. Hearing & balance

Continuous with nasopharynx via auditory (Eustachian) tube Continuous with mastoid cells via mastoid aditis & antrum Lined with modified respiratory-type mucosa Atmospheric pressure maintained in tympanic cavity via auditory tube (tensor veli palatini m. via CN V3; salpingopharyngeus m. via CN X) Tympanic Cavity (Middle Ear) Kingsley Concise Text of Neuroscience

Middle Ear Ossicles Tympanic membrane Malleus (attached to tympanic membrane) Incus Stapes (footplate overlies oval window) Round window Cochlear apex Cochlear base Movement of ossicles controlled by: Tensor tympani m. (CN. V3) Stapedius m. (CN VII)

Inner Ear Kingsley Concise Text of Neuroscience

Color Textbook of Histology, 2nd Ed., p. 526 Inner Ear - Bony Labyrinth Interconnecting cavities within petrous temporal bone

Inner Ear - Bony Labyrinth Contents: Perilymph (similar to CSF) Membranous labyrinth Color Textbook of Histology, 2nd Ed., p. 526

Cochlea duct Saccule Utricle 3 Semicircular ducts Hearing Head orientation & movement Inner Ear - Membranous Labyrinth

Content: Endolymph (resembles intracellular fluid; high [K], low [Na]) Sensory epithelium of auditory & vestibular system Color Textbook of Histology, 2nd Ed., p. 526 Endolymphatic duct & sac Inner Ear - Membranous Labyrinth

Cochlea Round window Cochlear apex Cochlear base Cochlear base (at oval window) 2.75 turns to cochlear apex

Osseous Spiral Lamina Modiolus Spiral Ganglion Cochlear Nerve Fibers (auditory component of CN VIII) Cochlea

Wheater’s Functional Histology, 4th Ed., p. 398 Modiolus Osseous Spiral Lamina Spiral Ganglion Nerve Fibers (auditory component of CN VIII) Cochlea

Scala vestibuli – helicotrema – scala tympani (perilymph filled) Scala media = cochlear duct (endolymph filled) Cochlea (Uncoiled) scala= L. staircase Principles of Neural Science, 3rd Ed., Appleton & Lange, 1991 Auditory (Eustachian) tube

Oval window (fenestra vestibuli) covered by footplate of stapes Round window (fenestra cochlea) covered by secondary tympanic membrane Cochlear “Windows” Principles of Neural Science, 3rd Ed., Appleton & Lange, 1991 Auditory (Eustachian) tube

HarperCollins College Publishers, 1993 Scala vestibuli Scala tympani Scala media = Cochlear duct

Stria vascularis Vestibular membrane Basilar membrane Reissner’s HarperCollins College Publishers, 1993

Wheater’s Functional Histology, 4th Ed., p. 398 SV ST SM VM BM Compartments: Scala vestibuli Scala media Scala tympani Membranes: Vestibular membrane* Basilar membrane * Reissner’s membrane

Organ of Corti on Basilar Membrane to modiolus SV ST VM BM Stria vascularis N Young & Heath Wheater’s Functional Histology to modiolus

Young & Heath Wheater’s Functional Histology to modiolus IHC OHC Organ of Corti on Basilar Membrane

to modiolus HarperCollins College Publishers, 1993 Organ of Corti (on basilar membrane): Inner hair cells (IHC: 1 row) Outer hair cells (OHC: 3-5 rows) Supporting cells (pillar cells) Tectorial membrane (gelatinous mass) IHC OHC

Cochlear Hair Cells Specialized apical membrane containing stereocilia (“hairs”) Stereocilia all oriented similarly, with shortest stereocilia located toward modiolus Rows of stereocilia connected by tip links Stereocilia of OHC embedded in tectorial membrane Deflection of stereocilia toward taller stereocilium depolarizes hair cell membranec

Basilar membrane Basilar membrane Supports organ of Corti Variations in width and stiffness resonate with different frequencies Deflection of stapes footplate sets up fluid motion in perilymph of scala vestibuli -- displaces the basilar membrane Apex Base Base (near oval window) Thin (100 μm) and stiff High frequency Apex Low frequency Thick (500 μm) & flexible Basilar membrane thickness

Cochlear Innervation Afferents: Cochlear nerve (from organ of Corti in cochlea; cell bodies in cochlear ganglion) Inner hair cells = sound detection Outer hair cells = unclear function; can contract Efferents: synapse on OHC and afferents of IHC REFLEX CONTROLS: Control movement of tympanic membrane Tensor tympani muscle (mandibular nerve, CN V3) Control movement of stapes Stapedius muscle (facial nerve, CN VII) Control of basilar membrane movement OHC (cochlear n., CN VIII)

Kingsley Concise Text of Neuroscience Vestibular Apparatus 3 Semicircular canals Vestibule 3 Semicircular ducts Utricle Saccule

Kingsley Concise Text of Neuroscience Sensory Hair Cells of the Vestibular Apparatus Hair cells Type I (bulbous) & Type II (columnar); functional difference? 1 kinocilium (w/ basal body) plus many stereocilia (tallest stereocilia adjacent to kinocilium) Supporting cells Secrete glycoprotein (forming gelatinous plaque into which “hairs” are embedded) Efferent nerves project from the CNS to Type I and II hair cells (~ modulate transduction)

Semicircular Canals & Ducts Semicircular DuctsOrientation Anterior (superior)Vertical plane PosteriorVertical plane Lateral (horizontal)Transverse plane

Sensory Organ of Semicircular Ducts Crista ampullaris Located in ampulla of each semicircular canal Ridge of supporting tissue, oriented perpendicular to endolymph flow Stereocilia & single kinocilium embedded in cupula (gelatinous glycoprotein) Color Textbook of Histology, 2nd Ed.,

Wheater’s Functional Histology, 4th Ed., p. 404 Remnant of cupula Nerve fibers (vestibular part of CN VIII) Hair cells Sensory Organ of Semicircular Ducts Crista ampullaris

Move head: Inertia of endolymph displaces cupula in opposite direction Stereocilia are deflected with the cupula (either towards or away from kinocilium) Crista ampullaris senses changes in direction & rate of movement of head (e.g., nodding or shaking the head) - not constant motion

Semicircular canals are aligned & function in contralateral pairs: Left anterior & right posterior ducts Left posterior & right anterior ducts Left horizontal & right horizontal ducts Sensory information from cristae ampullaris: angular acceleration of head in the plane of the semicircular canal

Kingsley Concise Text of Neuroscience Vestibular Apparatus

Color Textbook of Histology, 2nd Ed., p. 528 Sensory Organs of Saccule & Utricle Macula (otolith organ) Stereocilia & single kinocilium embedded in otolithic membrane that contains otoliths (calcium carbonate crystals) striola

Anatomical Polarization of Hair Cells in Maculae 1.Arrangement of hair cells on either side of striola 2.Striola bend about 90 o across the macula 3.Saccule and utricle are oriented perpendicular to one another Saccule receptor cells lie in the sagittal (vertical) plane Utricle receptor cells lie in the horizontal plane

Otoliths deflect otolithic membrane downward in response to gravity when head is shifted from position of equilibrium

Any linear movement of the head will stimulate macular hair cells Sensory information from maculae: Linear acceleration (e.g., starting or stopping forward movement) Static position of head in space

Cochlear duct Spiral ganglion Cochlear nerve Vestibular nerve Superior (Anterior) Lateral/ Horizontal Posterior Saccular maculae Vestibular (Scarpa’s) ganglion Semicircular canals Utricular maculae Crista ampullaris Macula

Biknevicius website biknevicius/teaching.htmhttp:// biknevicius/teaching.htm