1. Special sense organs
Shiping Ding

2. Eyes: visual organ, photoreceptors and auxiliary structure
Ears: the organ of hearing and equilibrium, which mediates the senses of equilibrium and hearing via mechanoreceptors in the vestibulocochlear apparatus

3. 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.

4. THE EYE Internal anatomy of the eye
The sagittal section of an eye shows the interrelationships among the major ocular structures, the three major layers or tunics of the wall, important regions within those layers, and the refractive elements (cornea, lens, and vitreous).
Internal anatomy of the eye
The sagittal section of an eye shows the interrelationships among the major ocular structures, the three major layers or tunics of the wall, important regions within those layers, and the refractive elements (cornea, lens, and vitreous).

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

6. Eyeball Walls

7. Cornea 5 layers: epithelium Bowman’s membrane Stroma
Colorless, transparent
5 layers:
epithelium
Bowman’s membrane
Stroma
Descemet’s membrane
endothelium
The anterior structure of the eye, the cornea has five layers. (a) The external stratified squamous epithelium (E) is nonkeratinized, five or six cells thick, and densely supplied with sensory-free nerve endings that trigger the blinking reflex. The stroma (S) comprises approximately 90% of the cornea’s thickness, consisting of some 60 layers of long type I collagen fibers arranged in a precise orthogonal array and alternating with flattened cells called keratocytes. The stroma is lined internally by endothelium (EN). (X100; H&E)

8. b.Bowman’s membrane( anterior basement membrane)
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
keratin

9. C. Stroma or substantia propria
Several lamellae of fine collagen fibrils network
Flattened fibroblasts
G.S.rich in chrodroitin sulfate and keratan sulfate, which help maintain the precise organization and spacing of the collagen fibrils
D. Descemet’s membrane (posterior basement membrane)
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
lamellae of fine collagen f.network
fibroblasts

10. The reasons of cornea transparent
No blood vessels & pigments
Basal of epithelium is plane
Uniform spacing of collagen fibrils and lamellae in stroma
Ground Substance with transparent nature & maintains proper water

11. 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)
The retina is the thick layer of the eye immediately inside the choroid. (a) The central retinal artery and vein pass through the optic nerve and enter the eye at the optic disc where they divide to form smaller lateral branches in the retina’s nerve fiber layer. Capillaries extend as deep as the inner nuclear layer. (Nutrients and O2 for the outer retinal layers diffuse from capillaries in the choroid.)
(b) The layers and major neurons of the retina and their general organization are shown schematically here; the supporting Müller cells which penetrate all the neural layers are not shown.
(c) The optic disc (OD) at the head of the optic nerve (ON) is the point at which ganglionic layer axons from all regions of the retina (R) converge, penetrate the choroid and sclera (S), and leave the eye as the optic nerve to enter the brain. Blood vessels (BV) in the ganglionic and nerve fiber layers converge at the optic disc to form the central artery (CA) and vein of the retina within the optic nerve. (X40; H&E)
(d) The fovea (F) is a small specialized area of the retina where cell bodies and axons of the ganglionic and inner layer are largely dispersed peripherally, thinning this retinal area and allowing light to hit the cones with very little light scattering. The fovea contains no rods and a greatly increased density of cones, causing the layer with their cell bodies to be slightly thicker here than elsewhere. These and other structural modifications at the fovea provide this area of the retina with the greatest visual acuity or sharpness of visual detail, but only when adequate light is present. The surrounding choroid (C) and sclera (S) are also shown. (X100; H&E)

12. Layers of the retina
the inner limiting membrane (ILM), a basement membrane covered by expanded processes of Müller cells, which are not distinguishable in routine preparations.
the nerve fiber layer (NFL), containing the ganglionic cell axons, which converge at the optic disc and form the optic nerve.
the ganglionic layer (GL), containing cell bodies of the ganglion cells and thicker near the retina’s center than its periphery.
the inner plexiform layer (IPL), containing fibers and synapses of the ganglion cells and the bipolar neurons of the next layer.
the inner nuclear layer (INL), with the cell bodies of several types of bipolar neurons, which begin to integrate signals from the rod and cone cells.
the outer plexiform layer (OPL), containing fibers and synapses of the bipolar neurons and rod and cone cells.
the outer nuclear layer (ONL), with the cell bodies and nuclei of the photosensitive rod and cone cells.
the outer limiting layer (OLL), a line formed by junctional complexes holding the rod and cone cells to the intervening Müller cells.
the rod and cone layer (RCL), which contains the outer segments of these cells where the photoreceptors are located.
the non-neural pigmented layer (PL), which has several supportive functions important for the function and maintenance of the neural retina. (X150; H&E)

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

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

15. Optical cells
bipolar neurons
The rods and cones

16. 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)

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

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

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

20. 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.

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

22. Ear External ear ： auricle Middle ear： Inner ear
external acoustic meatus
tympanic membrane
Middle ear：
tympanic cavity
auditory tube
mastoid process
Inner ear
sensory of hearing and balance

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

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

25. 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
(a) Two sensory areas called maculae occur in the membranous labyrinth of the vestibular utricle and saccule, both specialized for detecting gravity and endolymph movements.
(b) A more detailed diagram of a macular wall shows that it is composed of hair cells, supporting cells, and endings of the vestibular branch of the eighth cranial nerve. The apical surface of the hair cells is covered by a gelatinous otolithic layer or membrane and the basal ends of the cells have synaptic connections with the nerve fibers. The SEM shows otoliths embedded in this membrane. These mineralized structures make the otolithic membrane heavier than endolymph alone, which facilitates bending of the kinocilia and stereocilia by gravity or movement of the head.
(SEM, used with permission from David J. Lim, House Ear Institute and Department of Cell & Neurobiology, University of Southern California, Los Angeles, CA.)
(c) A diagram of a single generalized hair cell shows the numerous straight stereocilia, which contain bundled actin, and a longer single kinocilium, a modified cilium whose tip may be slightly enlarged.
(a) This diagram shows the two types of hair cells in the maculae and cristae ampullares. Basal ends of type I hair cells are rounded and enclosed within a nerve calyx on the afferent fiber. Type II hair cells are columnar and associated with typical bouton synaptic connections to their afferents. Both types are also associated with efferent fibers.
(b) A more detailed diagram shows that stereocilia occur in rows of increasing height, with the tallest next to the single kinocilium on one side of the cell. By TEM the end of each stereocilium shows an electron-dense region containing cation channels and proteins involved in mechanoelectrical transduction (MET), which converts mechanical activity of the stereocilia to electrical activity. Neighboring stereocilia are connected by proteins of various side links; the best understood of these are the tip links connecting the tips of stereocilia and contain very long cadherin proteins. Changes in the tension of the tip links caused by bending of the hair bundle open or close the adjacent mechanically gated K+ channels and change the afferent synaptic activity of the hair cells.

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

27. The spiral organ of Corti
The position of cochlear duct within the turns of the bony cochlea
The scala vestibuli and the scala tympani, containing perilymph
The scala media containing endolymph

28. 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

29. Sounds Pathway
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 vibrates
Vibrate the stereocilia of the hair cells and initiate neuronal transduction

30. 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.

31. 1. Which of the following is the thickest component of the cornea?
a. Corneal epithelium
b. Stroma
c. Descemet membrane
d. Bowman membrane
e. Corneal endothelium
2. Which cells transmit visual signals from the retina to the brain?
a. Bipolar cells
b. Amacrine cells
c. Ganglion cells
d. Horizontal cells
e. Müller cells
3. The epithelial cells within the organ of Corti are supported by which of the following structures?
a. Spiral limbus
b. Tectorial membrane
c. Vestibular membrane
d. Basilar membrane
e. Spiral ligament

32. Thanks for your attention