EYES AND EARS

GENERAL DESCRIPTION Eyes: visual organ Ears: the organ of hearing and equilibrium. The equilibrium sense, generally associated with balance, provides feedback about the positions and movements of our heads and bodies in space.

OBJECTIVES Know the general layers of the eye. Describe the structure of Cornea and its reason of transparent. Describe the structure of Retina and the function of pigment cell, rod cell and cone cell. Know the definition of Ora serrata, Macula lutea, Fovea centralis and Optic disc. Know the general structure of ear. Describe six sensory regions of the membranous labyrinth and their function.

THE EYE

eye Fibrous layer Walls Vascular layer eyeball Retina Content：Aqueous humor、Lens、 Vitreous body Accesory structure:Eyelid、Muscles of the eye、Lacrimal gland

Ciliary body Eyeball Walls Cornea 1/6 Fibrous layers Sclera 5/6 Eye ball Vascular layers Retina Sclera 5/6 Choroid 2/3 Ciliary body Iris

Cornea Colorless, transparent 5 layers: epithelium Bowman’s membrane Stroma Descemet’s membrane endothelium

Cornea keratin a.epithelium: Non-keratinized stratified squamous epi. 5-6 layers Numerous mitotic figures No vessels. Free nerve ending b.Bowman’s membrane( anterior basement membrane) An accellular homogeneous membrane (collagen fibrils) Stability & strength, no regeneration

C. Stroma or substantia propria Several lamellae of fine collagen f.network Flattened fibroblasts G.S.rich in chrodroitin sulfate D. Descemet’s membrane (posterior limiting lamina) Acellular homogeneous membrane Can be repaired by endothelial cells E.Endothelium Like mesothelium in its morphology Regulate the water content of the stroma  maintain transparency

胶原板层电镜图 相邻胶原板层的纤维方向垂直 胶原板层纵断面 胶原板层横断面

胶原板层结构 lamellae of fine collagen f.network fibroblasts

The reasons of cornea transparent No blood vessels & pigments Basal of epi. is plane Uniform spacing of collagen fibrils and lamellae in stroma G.S. with transparent nature & maintains proper water

Retina Two regions: The nonphotosensitive region (nonvisual part) Located anterior to the ora serrata, no photoreceptors. The photosensitive region (optic part) Lines the inner surface of the eye posterior to the ora serrata (except the optic papilla)

Retina 4 layers of cells: Pigment cells Optic cells Bipollar cells Ganglion cells

Pigment epithelium Structure： 1) Simple cuboidal epi. Attached to choroid and easy separated from retina (detachment of retina) 2) Junctional complex , 3) Melanin granules 4) Processes (contain pigment granules) Function： absorb light,protect rod and cone from strong light Blood-retina barrier 3) Phagocytize the membranous discs from retinal photoreceptor cells 4) Store vitamin A to assist in forming rhodopsin

Optical cells bipolar neurons The rods and cones Glial cells（Müller cell）

Rod cell Thin,elongated cells， about 120 million rods A body and two opposite processes Outer segment and inner segment separated discs ,shed disc phagocytized by pigment cells rhodopsin (visual purple) Function: sensitive to low intensity light Night vision (lack of vitamin A leads night blindness)

cone cell About 7 million cells Located in posterior part of retina,especially in fovea Outer and inner segments (conical) Continuous discs & not renewed Function 1）sensitive to high intensity light 2）color distinguishing（red、blue、green iodopsin） (photoactive substance)

Bipolar cells An axon & a dendrite Synapse with photoreceptor cells and ganglion cells Müller cells Extend entire thickness of retina Neuroglia Horizontal cells Amacrine cells

Ganglion cells The dendrite synapse with bipolar cells The axons concentrate together form optic nerve

Specilized regions of the retina Ora serrata ：neural layer ends anteriorly at ciliary body,pigment cells extend to cover posterior iris Macula lutea:directly on eye’s posterior pole. “yellow spot”,mostly cones Fovea centralis: central pit of macula,only cones, vision acuity straight on Optic disc:blind spot,no rods or cones,optic nerve exits,medial and inferior to fovea centralis.

10 layers 1 = pigmented epithelium 2 = layer of photoreceptors 3 = external limiting membrane 4 = outer nuclear layer 5 = outer plexiform layer, where photoreceptors synapse 6 = inner nuclear layer of bipolar neurons 7 = inner plexiform layer, where bipolar neurons synapse with ganglion cells 8 = ganglion cell layer 9 = optic nerve layer 10 = internal limiting membrane

Visual pathways light cornea champer lens vitreous body retina pigment epithelium rods and cones bipolar cells ganglion cells optic nerve fibers

Ear External, middle, inner ear External and middle ear: gathers and funnels sound waves Inner ear: sensory of hearing and balance

(auricle) External ear ： auricle Middle ear： Mastoid process external acoustic meatus tympanic membrane Middle ear： tympanic cavity auditory tube mastoid process

Internal ear Bony labyrinth Membranous labyrinth Bony labyrinth： Semicircular canals Vestibule Cochlea Menbranous labyrinth： Cochlear labyrinth Vestibular labyrinth three semicircular ducts Utricle and saccule

Six sensory regions of the membranous labyrinth: Three crista ampullaris Two maculae(maculae of utricle, maculae of saccule) The spiral organ of Corti

Crita ampullaris three，located in the membranous ampullae of the semicircular ducts Composition： Supporting cells：support，forming cupula Sensory hair cells：with stereocilia and kinocilium are embedded in the cupula Function： sensors of angular acceleration of the head

壶腹嵴 de 功能 感受旋转运动

Maculae of utricle and saccule： Located in the vestibule Sense the position of the head and its linear movement

前庭的毛细胞

位觉斑 de 功能 直线运动开始和终止、头部静止的位觉。

Note： The position of cochlear duct within the 2.75 turns of the bony cochlea The scala vestibuli and the scala tympani, containing perilymph The scala media containing endolymph

Schematic diagram of the cochlea: Scala vestibuli Scala tympani

Corti’s organ：sensor of sound vibration On the lower wall of the scala media Tectorial membrane Inner (close to spiral lamina)and outer (farther from the spiral lamina) hair cells Supporting cells: inner and outer phalangeal cells pillar cells

Sounds Pathawy Sound comes Hits tympanic membrane to vibrate three auditory ossicles vibrate vibration at tympanic (oval) window Vibration in the perilymph of the scala vestibular to the scala media Vibrates of basilar membrane and tectorial membrane,and hair cells attached to also vibrates Vibrate the stereocilia of the hair cells and initiate neuronal transduction

Clinical Correlation Vertigo: dysfunction of vestibular system Causes: viral infections, certain drugs, tumors, excessive stimulation (seasickness, carsickness, or airsickness) Hearing loss 1)Conductive hearing loss: sound waves are mechanically impeded from reaching the auditory sensory receptors within the internal ear.such as excessive accumulation of cerumen. 2)Sensorineural hearing impairment: injury to the auditory hair cells or the cochlea nerve. May be congenital or acquired. Causes include infections, trauma (exposure to excessive noise), administration of certain antibiotics, aging.

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