EARConsists of 3 parts:1. EXTERNAL EAR – receives sound waves2. MIDDLE EAR – sound waves are transmitted from air to bone & by bone to internal ear3. INTERNAL EAR – vibrations are transduced to specifc nerve impulses that pass via acoustic nerve to CNS; also contains vestibular organs which maintains equilibrium
Objectives1. Describe the histology of • Describe the otolith. external, middle, and inner • Identify the ff. in a section of ear & tympanic membrane the cochlea under LM:2. Describe the histology of – Spiral lamina the ff.: – Scala vestibulii 1. Macula of the saccule/utricle – Vestibular membrane 2. Crista ampullaris – Cochlear duct 3. Organ of Corti – Tectorial membrane 4. Vestibular membrane – Basilar membrane3. Trace conjunction of sound – Scala tympani vibrations from the – Organ of Corti tympanic membrane to the – Mociolis organ of Corti. – Cochlear nerve – Spiral ganglion
PARTS OF THE EAR A, Auricle B, External auditory meatus C, Tympanic membrane D, Semicircular canals E, Vestibule F, Cochlea
EXTERNAL EAR• Skin of the auricle = keratinized stratified squamous epithelium (not shown)• Dermis – with small hair follicles – DCT continuous w/ perichondrium that surrounds elastic cartilage (located in the center of the structure) – Elastic cartilage imparts flexibility to the auricle
External Auditory Meatus• The skin lining the external auditory meatus (canal) is generally thin but contains hair follicles and large ceruminous glands that extend through the dermis to reach the perichondrium of the cartilagenous part of the tube.• Hairs - aid in preventing intrusion of insects into the ear canal• Ceruminous gland – has a large lumen – either cuboidal (inactive) or columnar (active) epithelium – closely resembles axillary apocrine sweat glands. – coiled tubular apocrine sweat gland• Cerumen – waxy secretion of the ceruminous glands may protect the skin from desiccation and irritation – yellowish, semisolid mixture of wax and fats
External Auditory Meatus F – Hair Follicles G – Ceruminous Gland
Tympanic Membrane (Eardrum)• Oval membrane; epithelial sheet• External surface is covered with a thin layer of epidermis• Inner surface is covered with simple cuboidal epithelium continuous with the lining of the tympanic cavity• Between the 2 epithelial coverings is a tough connective tissue layer composed of collagen, elastic fibers, & fibroblasts• Fxn: Vibrations of the tympanic membrane produced by sound waves transmit sound wave energy to the middle and inner ear
Tympanic cavity• Air-filled• Irregular space that lies within the temporal bone between the tympanic membrane and the bony surface of the internal ear• Communications: – Anterior: communicates with the pharynx via the auditory tube (Eustachian tube) – Posterior: smaller, air-filled mastoid cavities of the temporal bone.• Lined mainly with SIMPLE CUBOIDAL EPITHELIUM resting on a thin lamina propria that is strongly adherent to periosteum.• Near the auditory tube, this simple epithelium is gradually replaced by the CILIATED PSEUDOSTRATIFIED COLUMNAR EPITHELIUM lining the tube.
Auditory ossicles• Series of small bones that connects tympanic membrane to the oval window• transmit the mechanical vibrations of the tympanic membrane to the internal ear• covered with SIMPLE SQUAMOUS EPITHELIUM• Three ossicular bones: 1. MALLEUS – “hammer”; attached to connective tissue of the tympanic membrane 2. INCUS – “Anvil” 3. STAPES – “Stirrup”;attached to connective tissue that of the membrane in the oval window
Tympanic Membrane & Ossicles 3 Layers of Tympanic Membrane C – cuticle layer (external) - consist thin layer of skin Fi – fibrous layer - type I & Type II collagen M – mucus layer (internal) - cuboidal cells Ossicles CB – Compact Bone Ca - Cartilage Mu – Tensor Tympani Muscle
Bony Labyrinth• lined with endosteum• separated from the membranous labyrinth by the perilymphatic space – This space is filled with a clear fluid called the perilymph, within which the membranous labyrinth is suspended.Three components: 1. Semicircular canal 2. Vestibule 3. Cochlea
Bony Labyrinth• Semicircular Canals (SC) • Cochlea – Sup, pos, lateral – Hollow, bony spiral that – One end of each canal is turns around itself like a enlarged (ampulla) snail around central bony – Enclose semicircular ducts column (Modiolus) – Contains cochlear duct• Vestibule – Central region bet SC & cochlea – Houses saccule & utricle – also contains oval (where stapes is related) and round window
B – BoneSC – Semicircular CanalsArrow - Fibroblast
COCHLEA OF THE INNER EARA. Anatomy of bony labyrinthB. Anatomy of the membranous labyrinthC. Sensory labyrinth.
Membranous Labyrinth• epithelium derived from the embryonic ectoderm which invades the developing temporal bone• Contains circulating endolymphSpecialized Areas: – Saccule & Utricle – Semicircular ducts – Cochlear duct
ML - MembranousLabyrinth(Lined by SQUAMOUSEPITHELIUM)
SACCULE & UTRICLE• thin sheath of connective tissue lined with simple squamous epithelium• Consist of MACULA – neuroepithelial cells innervated by vestibular nerve – receptors for sensing orientation of the head relative to gravity (saccule) & acceleration (utricle) – Consist of the ff cells: • Receptor Hair Cells • Supporting Cells • Aff & eff nerve endings
Macula of the saccule -ilocated in thewall, thus detecting linear verticalaccelerationMacula of the utricle located in the floor, thus detectinglinear horizontal acceleration).
Macula of the Saccule & Utricle Consist of two types of cells: • Supporting cells – Columnar; with nuclei nearest the basement membrane • Sensory receptor (or hair) cell 2 Types of Hair cells: a) Type I hair cells (flask shaped) b) Type II hair cells (cylindrical) • Both have nerve terminals & stereocilia • Also possess OTOLITHIC MEMBRANE – gelatinous membrane of glycosaminoglycans that contains crystals of calcium carbonate & protein (OTOLITHIS)It is difficult to resolve the two types of hair cells in light micrographs. In this image, the morerounded cells are most likely type I hair cells.
Hair Cells• Type I hair cells – GOBLET cells – bulbous in shape and stain poorly – nuclei tending to lie at a lower level than type II – invested by a meshwork of dendritic processes of afferent sensory neurones• Type II hair cells – COLUMNAR CELLS – more slender in shape – have only small dendritic processes at their bases SUPPORTING CELLS
SEMICIRCULAR DUCT• Arise/ continuation of utricle• Ampullae – expanded regions at its lateral ends• Receptor Organ: CRISTAE AMPULLARES• Composed of – Supporting cells • sit on the basal lamina – Hair cells • type I and type II hair cells, exhibit the same morphology as the hair cells of the maculae – Cupula • a gelatinous glycoprotein mass overlying the cristae ampulares • similar to the otolithic membrane in structure and function • cone-shaped and does not contain otoliths
Crista AmpularisBlack & Green Arrow – CupulaRed - Type I Hair cellYellow - Supporting cells
COCHLEAR DUCT • a diverticulum of the saccule • highly specialized as a sound receptor • surrounded by perilymphatic spaces • appears to be divided into three spaces: – SCALA VESTIBULI (above) • Contains PERILYMPH – SCALA MEDIA (cochlear duct) in the middle • Contains ENDOLYMPH • Roof: vestibular (Reissner’s) membrane • Floor: basilar membrane – SCALA TYMPANI • Contains PERILYMPHThe SV & ST are continuous (from oval window to round window) & communicate at theapex of the cochlea via an opening known as the helicotrema.
COCHLEAO – Organ of CortiSV – Scala VestibuliSM – Scala MediaST – Scala Tympani
COCHLEAR DUCT (Scala Media) Parts1. Vestibular (Reissners) 3. Stria Vascularis Membrane – pseudostratified epithelium – consists of 2 layers of – contains intraepithelial plexus of squamous capillaries epithelium, derived from – Covers lateral wall of cochlear duct, b/w scala media & scala vestibular membrane & spiral vestibuli prominence – preserve very high ionic – responsible for ionic comp of gradients across endolymph membrane 4. Spiral prominence2. Basilar Membrane – in inferior portion of lateral wall of – supports the organ of Corti cochlear duct – composed of two zones: – small protuberance that juts out from • Zona arcuata - thinner, lies the periosteum of cochlea into cochlear more medial duct • Zona pectinata - similar to a fibrous meshwork – Continious with stria vascularis cells containing a few fibroblasts • These cells are reflected into the spiral sulcus, where they become cuboidal • Cells of this layer continue onto the basilar lamina as the cells of Claudius, which overlie the smaller cells of Böttcher
COCHLEAR DUCT Parts5. Limbus of the Spiral Lamina 6. Tectorial membrane – Locates at the narrowest – proteoglycan-rich portion of the cochlear gelatinous mass duct, where vestibular & – contains numerous fine basilar membranes meet keratin-like filaments – Formed from the bulging out – overlies organ of Corti of the periosteum (into the – where the stereocilia of scala media) covering the hair cells of the organ of spiral lamina Corti are embedded – Part of the limbus projects over – Secreted by interdental the internal spiral sulcus cells (found in the body of (tunnel). spiral limbus)
ORGAN OF CORTI• receptor organ for hearing• lies on the basilar membrane• composed of hair cells and supporting cells.
O osseous spiral lamina SL spiral limbus SLig spiral ligament SM scala mediaT tunnel of Corti TM tectorial membrane Svasc Stria Vascularis
Organ of Corti – Supporting CellsINNER AND OUTER PILLAR CELLS (IP & OP) INNER PHALANGEAL CELLS – tall cells with wide bases and apical end – located deep to the inner pillar cells – shaped like an elongated "I" – completely surround the inner hair cells they – attached to the basilar membrane, and support each one arises from a broad base – support the hair cells of the organ of Corti BORDER CELLS Inner tunel – delineate the inner border of the organ of – Medial wall formed by IP Corti – Lateral wall: OP – slender cells that support the inner aspects of IP >OP (usu 3 IP vs 2 OP. the organ of CortiOUTER PHALANGEAL CELLS CELLS OF HENSEN – tall columnar cells attached to the basilar – define the outer border of the organ of Corti membrane – tall cells – With cup-shaped apex – b/w outer phalangeal cells & shorter cells of – support the basilar portions of outer hair Claudius, which rest on the underlying cells of cells along with bundles of eff & aff nerve Böttcher. fibers (which pass between them on their way to the hair cells) – Found below the hair cells Space of Nuel - fluid-filled gap around unsupported regions of the outer hair cells that conects with inner tunnel
Organ of Corti - Hair Cellsspecialized for transducing impulses for the organ of hearingHas TWO TYPES (depending on location) Inner hair cells Outer hair cells – single row of cells supported – supported by outer by inner phalangeal cells phalangeal cells – extend the inner limit of the – near the outer limit of the entire length of organ of Corti organ of Corti – Short – elongated cylindrical cells – centrally located nucleus – nuclei are located near their – w/ stereocilia ( "V" shape) bases – No kinocilium – W/ stereocilia ("W”-shaped ) – basal aspects of these cells – synapse with afferent and synapse with afferent efferent fibers on its base cochlear nerve – Nokinocilium – arranged in rows of three (or four) along the entire length of this organ
Description of Image• The organ of Corti contains a single row of inner hair cells (arrow) nestled in cytoplasmic recesses of the inner phalangeal cells. Thus, the inner hair cells do not touch the basilar membrane.• The inner hair cells have a rounded base and a short neck, similar in appearance to the type I hair cells of the cristae and maculae. Their apical surface has 50 to 70 stereocilia.• In addition to the phalangeal cells, the inner hair cells are held close to the tectorial membrane by cytoplasmic extensions from the inner pillar cells (arrowhead). These cell processes contain aggregations of microtubules.• There are three to five rows of outer hair cells (curved arrow) and one row of inner hair cells in the organ of Corti. The outer hair cells are cylindrical in shape, similar to the type II hair cells of the cristae and maculae.• The outer hair cells do not rest directly on the basilar membrane; they are cradled by the outer phalangeal cells (arrow). Recall that the inner hair cells are also supported by the inner phalangeal cells. Thus, each row of hair cells has a corresponding row of phalangeal cells.• Fingerlike extensions of the phalangeal cytoplasm abut the apical cytoplasm of the hair cells to keep these cells close to the tectorial membrane. These cytoplasmic areas of the phalangeal cells contain bundles of microtubules. The phalangeal cells and the inner and outer pillar cells (arrowheads) provide the major structural support for the hair cells.
Tips• Pag nasa side ng Tectorial membrane, “INNER” un (meaning inner cell or if sa baba nun inner phalangeal cell)• Mas marami ang rows ng Outer hair cell kesa sa Inner hair cell.• For the pillar cells, nasa paligid lang siya ng inner tunnel. Again, pag nasa side ng tectorial membrane inner pillar (usu mas marami din)