SPECIAL SENSES - EARS

2015 -Section A Laboratory Trans

A. B. C.HANDOG NG

Anj Barbin Claresse

EAR

Consists of 3 parts: 1. EXTERNAL EAR – receives sound waves 2. MIDDLE EAR – sound waves are transmitted from

air to bone & by bone to internal ear 3. INTERNAL EAR – vibrations are transduced to

specifc nerve impulses that pass via acoustic nerve to CNS; also contains vestibular organs which maintains equilibrium

Objectives

1. Describe the histology of external, middle, and inner ear & tympanic membrane

2. Describe the histology of the ff.:

1. Macula of the saccule/utricle2. Crista ampullaris3. Organ of Corti4. Vestibular membrane

3. Trace conjunction of sound vibrations from the tympanic membrane to the organ of Corti.

• Describe the otolith.• Identify the ff. in a section of the

cochlea under LM:– Spiral lamina– Scala vestibulii– Vestibular membrane– Cochlear duct– Tectorial membrane– Basilar membrane– Scala tympani– Organ of Corti– Mociolis– Cochlear nerve– Spiral ganglion

PARTS OF THE EAR

A, AuricleB, External auditory meatusC, Tympanic membraneD, Semicircular canalsE, VestibuleF, 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

DCT

HAIR FOLLICLE

ELASTIC CARTILAGE

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 Ear (ceruminous

gland)

External Auditory Meatus

F – Hair FolliclesG – 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

MIDDLE EAR

• Contents:– Tympanic Cavity/ Tympanic Membrane– Oval Window– Round Window– Ossicles• Malleus• Incus• Stapes

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 MembraneC – cuticle layer (external) - consist thin layer of skinFi – fibrous layer - type I & Type II collagenM – mucus layer (internal) - cuboidal cells

OssiclesCB – Compact BoneCa - CartilageMu – Tensor Tympani Muscle

INTERNAL EAR

• Bony Labyrinth• Membranous Labyrinth

Summary:

Bony Labyrinth

Membranous Labyrinth

Receptor Organs Functions

Vestibule Saccule & Utricle

Macula Equilibrium (Linear acceleration)

Semicircular Canal

Semicircular Duct

Crista Ampullaris

Equilibrium (Angular acceleration)

Cochlea Cochlea Organ of Corti Hearing

Middle & Inner Ear

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 canal2. Vestibule3. Cochlea

Bony Labyrinth

• Semicircular Canals (SC)– Sup, pos, lateral– One end of each canal is

enlarged (ampulla) – Enclose semicircular ducts

• Vestibule– Central region bet SC &

cochlea– Houses saccule & utricle– also contains oval (where

stapes is related) and round window

• Cochlea– Hollow, bony spiral that

turns around itself like a snail around central bony column (Modiolus)

– Contains cochlear duct

B – BoneSC – Semicircular CanalsArrow - Fibroblast

COCHLEA OF THE INNER EARA. Anatomy of bony labyrinthB. Anatomy of the membranous labyrinth C. 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 - Membranous Labyrinth(Lined by SQUAMOUS EPITHELIUM)

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 the wall, thus detecting linear vertical accelerationMacula of the utricle located in the floor, thus detecting linear horizontal acceleration).

Macula of the Saccule & UtricleConsist of two types of cells: • Supporting cells

– Columnar; with nuclei nearest the basement membrane

• Sensory receptor (or hair) cell2 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 more rounded cells are most likely type I hair cells.

Macula of the Utricle

Arrow – otolithsArrow head - stereocilia

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

Semicircular Ducts (Crista Ampullaris)

Crista Ampularis

Black & 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 PERILYMPH

The SV & ST are continuous (from oval window to round window) & communicate at the apex of the cochlea via an opening known as the helicotrema.

Inner Ear: COCHLEA (vertical section)

COCHLEA

O – Organ of CortiSV – Scala VestibuliSM – Scala MediaST – Scala Tympani

COCHLEAR DUCT (Scala Media) Parts1. Vestibular (Reissner's)

Membrane – consists of 2 layers of

squamous epithelium, derived from scala media & scala vestibuli

– preserve very high ionic gradients across membrane

2. Basilar Membrane– supports the organ of Corti – composed of two zones:

• Zona arcuata - thinner, lies more medial

• Zona pectinata - similar to a fibrous meshwork containing a few fibroblasts

3. Stria Vascularis– pseudostratified epithelium – contains intraepithelial plexus of

capillaries– Covers lateral wall of cochlear duct, b/w

vestibular membrane & spiral prominence– responsible for ionic comp of endolymph

4. Spiral prominence– in inferior portion of lateral wall of

cochlear duct– small protuberance that juts out from the

periosteum of cochlea into cochlear duct – Continious with stria vascularis cells

• 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 (Scala Media)

COCHLEAR DUCT & ORGAN of CORTI

A, Scala vestibuli B, Scala tympani C, Scala media (cochlear duct) D, Tectorial membraneArrowhead – Vestibular membrane Arrow – Basilar membrane Curved Arrow – Stria vascularis

Double arrowhead – Spiral prominence

COCHLEAR DUCT Parts

5. Limbus of the Spiral Lamina– Locates at the narrowest

portion of the cochlear duct, where vestibular & basilar membranes meet

– Formed from the bulging out of the periosteum (into the scala media) covering the spiral lamina

– Part of the limbus projects over the internal spiral sulcus (tunnel).

6. Tectorial membrane– proteoglycan-rich

gelatinous mass– contains numerous fine

keratin-like filaments– overlies organ of Corti– where the stereocilia of

hair cells of the organ of Corti are embedded

– Secreted by interdental cells (found in the body of 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 media T tunnel of Corti TM tectorial membrane Svasc Stria Vascularis

Organ of Corti – Supporting CellsINNER AND OUTER PILLAR CELLS (IP & OP)

– tall cells with wide bases and apical end– shaped like an elongated "I" – attached to the basilar membrane, and each

one arises from a broad base– support the hair cells of the organ of Corti Inner tunel– Medial wall formed by IP– Lateral wall: OP IP >OP (usu 3 IP vs 2 OP.

OUTER PHALANGEAL CELLS– tall columnar cells attached to the basilar

membrane– With cup-shaped apex – support the basilar portions of outer hair

cells along with bundles of eff & aff nerve fibers (which pass between them on their way to the hair cells)

– Found below the hair cells

INNER PHALANGEAL CELLS– located deep to the inner pillar cells– completely surround the inner hair

cells they support

BORDER CELLS – delineate the inner border of the

organ of Corti– slender cells that support the inner

aspects of the organ of Corti

CELLS OF HENSEN – define the outer border of the organ

of Corti– tall cells – b/w outer phalangeal cells & shorter

cells of Claudius, which rest on the underlying cells of Böttcher.

Space of Nuel - fluid-filled gap around unsupported regions of the outer hair cells that conects with inner tunnel

Organ of Corti - Hair Cells

Inner hair cells– single row of cells supported

by inner phalangeal cells– extend the inner limit of the

entire length of organ of Corti

– Short– centrally located nucleus– w/ stereocilia ( "V" shape)– No kinocilium – basal aspects of these cells

synapse with afferent cochlear nerve

Outer hair cells– supported by outer phalangeal

cells– near the outer limit of the organ

of Corti– elongated cylindrical cells– nuclei are located near their bases– W/ stereocilia ("W”-shaped )– synapse with afferent and efferent

fibers on its base– Nokinocilium– arranged in rows of three (or four)

along the entire length of this organ

specialized for transducing impulses for the organ of hearingHas TWO TYPES (depending on location)

orh

Arrowhead (left) – Inner Pillar cell Arrowhead (right) – Outer Pillar cellArrow - Outer Phalangeal cells Blue arrow – Tectorial membraneRed Arrow – Inner Hair cell Yellow Arrow – Outer Hair cell Curved Arrow – Hensen’s cell Diamond (green) – Inner Tunnel

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)

Spiral Ganglion

Spiral ganglion