1. Lab 6 VISION, EYEBALL MOVEMENT AND BALANCE SYSTEMS I

2. The 5 L’s Lower retina (upper visual field) Lateral part of LGN Loop of Meyer = Lower part (temporal) of optic radiations Lingual Gyrus In the conscious visual path, impulses travel from receptors in the retina to the visual cortex for perception of light stimuli. Visual impulses traverse rod and cone, bipolar, and then ganglion cells in the retina. Axons of ganglion cells exit the eyeball in the optic nerve and traverse the optic tract (after 50% decussation in the chiasm). The optic tract terminates in the lateral geniculate nucleus of the thalamus. Thalamic neurons then send axons through the optic radiations (retrolenticular fibers) to the primary visual (calcarine) cortex.

3. The eyeball consists of 3 concentric coats: (1) external or fibrous coat: sclera (posteriorly) and cornea (anteriorly) (2) middle or vascular coat: choroid, ciliary body, iris (3) internal or retinal coat: outer layer of pigmented cells and inner layers of neural elements posterior to the ora serrata The four refractive media

4. Black Board 42 Light

5. Black Board 40 -stratified non-keratinized squamous - the main layer of the cornea and consists of some 70 broad sheets of tightly bound, parallel collagen fibers embedded in an extracellular matrix -the direction of the collagen fibers differs in each layer for maximum mechanical strength - the absence of blood vessels in the cornea and the regular arrangement of the collagen fibers make the cornea translucent, allowing it to transmit light -adapted for ion-pumping -pumps fluid from the corneal stroma, preventing corneal opacification from excessive hydration

7. Lens Epithelium Aqueous Humor Lens Capsule The anterior and posterior aqueous chambers communicate with each other via the aperture of the pupil. Aqueous humor resembles cerebrospinal fluid in composition and is secreted by the epithelial cells of the ciliary processes in the posterior chamber. It flows from there to the anterior chamber through the pupil and provides nutrients to the structures that it bathes. The following figure indicates the path for the flow of the aqueous humor After filtering through a network of spaces (spaces of Fontana ) lined by endothelium (trabecular meshwork), which runs around the circumference of the root of the iris at the periphery of the anterior chamber, the aqueous humor enters the canal of Schlemm. This canal runs around the whole circumference of the limbus within the sclera and drains into venous vessels. It should be mentioned that there is normally a resistance to the flow of aqueous humor through the trabecular meshwork. Consequently, continued secretion and resorption of the aqueous humor is responsible for the normal intraocular pressure (10-22 mg Hg). Glaucoma results from abnormal drainage of the aqueous humor and is characterized by a rise in the intraocular pressure. If not treated, blindness can result from damage to the nerve cells of the retina.

8. The axons of the retinal ganglion cells all collect at the optic disc where they penetrate the sclera to form the optic nerve. This disc is also called the blind spot The pigmented, vascular layer, the choroid (the middle layer of the posterior 2/3 of the eyeball). extends from the ora serrata (the anterior margin of the neural retina) to the optic nerve contains blood vessels and lymphatics supporting the retina. It will appear as a dark brown sheet which blends with the sclera in its outer portion The inner portion is attached to the pigmented epithelium of the retina. Separation of the retina occurs between the rods and cones and the pigment epithelium The blood supply to the neural retina arises from the ophthalmic artery ( central artery of the retina and the ciliary arteries ). The central artery of the retina branches out from the region of the optic disc to serve inner portions of the retina (four branches go to the four quadrants of the retina). These branches are end arteries and, if occluded, will result in death of the ganglion cells and therefore total blindness from that quadrant of the eye. The posterior ciliary arteries penetrate the sclera around the optic disc and form the choroidocapillary plexus in the choroid. Materials from this plexus provide nutrients to the outer portions of the neural retina (the rods and cones).

10. Black Board 14 Vitreous body – Few scattered spindle shaped cells Fine highly dispersed collagen fibers ECM rich in Hyaluronic acid outer coat: sclera posteriorly cornea anteriorly middle coat: choroid layer, containing pigmented cells ciliary body (with unstained ciliary muscle) iris inner coat: retina (in general, deep to the pigmented layer)

12. Black Board 43 LENS is held in position by a suspensory ligament composed of zonular fibers. The lens is a soft, biconvex structure and has an outer capsule of hyaline material; the lens epithelium (below the capsule), which is a layer of cuboidal epithelial cells; the center region composed of tightly packed cells, which have lost their nuclei and are, chock full of special transparent proteins (crystallins).

13. Black Board 41

14. Black Board 15 Parasympathetic fibers from ciliary ganglion Cilliary Body Occulomotor N.  Edinger Westphall Pretectal Area

15. Black Board 44 note the thickened, black circular ciliary body, which extends from the base of the iris to the ora serrata (saw-toothed, black margin) at which point it is continuous with the choroid (the pigmented, vascular middle layer). The ciliary body contains the ciliary muscle (smooth muscle), which you will see in microscopic views. Contraction of this muscle decreases the tension on the suspensory ligament of the lens and allows the lens to round up and become more spherical. The iris is a sheet-like diaphragm anterior to the lens and separates the anterior and posterior chambers of the eyes. The pupil is the circular aperture, which can be constricted or dilated by the actions of the circular fibers of the constrictor pupillae (parasympathetic innervation) and radial fibers of the dilator pupillae (sympathetic innervation) muscles respectively (you will see muscles in the eyeball slide).

16. Black Board 16

17. Black Board 45

18. GROSS RELATIONS

19. Haines 3-7

20. Haines 2-26 Calcarine Cortex (V1, Area 17) is along banks of calcarine sulcus V2 and V3 surround V1 Upper visual field Lower visual field

21. Haines 3-4 optic tract - ends at lateral geniculate nucleus (not visible) optic nerve optic radiations

22. Haines 4-12 LGN is on Haines 4-13

23. Haines 4-13

24. Conscious Visual Path

25. Haines 4-1

26. Haines 5-36

27. Haines 4-34

29. Haines 5-26 Rostral Midbrain Level Optic Tract LGN

30. Black Board 20 Optic Radiations Optic Radiations are thalamic fibers traveling to the primary visual cortex