1. Special senses

2. Two types of peripheral nerve terminals Terminals of axons, which transmit impulses from the CNS to skeletal or smooth muscles (motor endings), or to glands (secretory endings) Terminals of dendrites, called sensory nerve endings or receptors, which perceive various stimuli and transmit this sensory input to the CNS

3. Receptors are classified into 3 types Exteroceptors – located near the body surface, are specialized to perceive stimuli from the external environment; other exteroceptors include receptors for vision, hearing, smell and taste Interoceptors – are specialized to perceive sensory information from visceral organs Proprioceptors – located in joint capsules, tendons, muscle spindles, inner ear, are specialized to perceive information that relates to an awareness of the body in space and movement

4. Eye: organ for visual perception

5. Anatomy of the eye

6. Tunica externa – Cornea – Sclera Tunica vasculosa – Choroid – Corpus ciliaris – Iris Retina – Fovea centralis (yellow spot) – Optic nerve disc (blind spot) – Pars iridica et pars ciliaris (non-visual retina)

7. Three layers of the eye

8. Important components of the eye Schlemm’s canal Anterior chamber Posterior chamber Pupil Ciliary processes Aqueous humor Ciliary muscle Lens Zonula fibers Corpus vitreum

9. Eye development

10. LM of the cornea

11. Cornea The cornea is the transparent bulging anterior 1/6 of the eye. Structure of the cornea: Anterior epithelium (stratified squamous non-keratinized with the naked nerve endings, responsible for corneal reflex) Bowman’s membrane Stroma (connective tissue lamina propria) Descemet’s membrane Posterior epithelium (corneal endothelium)

12. Sclera The white, opaque sclera covers the posterior five-sixths of the orb Sclera is composed of type I collagen fibers interlaced with elastic fibers Sclera is enveloped with the capsule of Tenon Thin layer of loose connective tissue between sclera and capsula of Tenon is called episclera

13. Anterior segment of the eye

14. Iris The iris, the colored anterior extension of the choroid, is a contractile diaphragm that controls the pupillary aperture. Its structure: Anterior surface covered by incomplete layer of fibroblasts and melanocytes Connective tissue stroma enriched with fibroblasts and melanocytes Dilator and sphincter pupillae muscle Posterior surface is smooth, covered by heavily pigmented melanocytes

15. Anterior segment of the eye

16. Ciliary body Ciliary muscle contraction has responsibility for the process called accomodation: contraction of ciliary muscle makes lens more convex, enabling focusing the eye on nearby objects Ciliary processes (about 70) radiate from the central connective tissue core towards the lens; ciliary processes produce aqueous humor Zonular fibers, radiating from the ciliary processes to insert into the lens capsule, regulate convexity of the lens

17. LM of iridocorneal angle

18. Aqueous humor turnover Ciliary processes produce aqueous humor which is responsible for the maintenance of intraocular pressure Corneo-scleral junction (limbus of the eye) houses canal of Schlemm, which is the site of outflow of the aqueous humor from the anterior chamber of the eye into the venous system

19. Ciliary body, iris, and pupil viewed from behind

20. Anterior segment of the eye, LM of the lens

21. The developing lens and SEM of mature lens fibers

22. Retina

23. Retina: 10 layers Pigmented epithelium Rods and cones photosensitive layer Outer limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Optic nerve fiber layer Inner limiting membrane

24. LM of the retina with its 10 layers

25. Retina: cellular composition Pigmented epithelium Photosensory (bipolar) neurons Bipolar (associative) neurons Horizontal cells (neurons) Amacrine cells (neurons) Muller cells (radial gliocytes) Ganglion cells (neurons)

26. Cellular composition of the retina

27. Rods and cones Light sensitive (photoreceptor) functions of the retina are attributed to rods and cones - modified dendrites of retinal photosensory neurons Rods are sensitive to dim light; each eye contains about 100-120 million rods; each rod consists of membranous discs, into which photosensitive pigment rhodopsin is incorporated There are 3 types of cones, which are sensitive to red, green, and blue lightwaves; each eye consist about 6 million cones, into membranous discs of which photopigment iodopsin is incorporated

28. Morphology of a rod and a cone

29. LM and EM of retinal rods

30. EM of rods (A, B) and of cones (C, D) fragments

31. EM of a retinal rod segments

32. Blood supply of the eye

33. Retina and choroid

34. Ora serrata, optic nerve disc, and fovea centralis

35. Eyelid

36. Eyelid and conjunctiva

37. Lacrimal apparatus

38. Ophtalmological pathologies Eyesore: non-transparent cornea Glaucoma: excess of intraocular pressure Cataract: non-transparent lens Presbyopia: decreased elasticity of the lens Eye floaters: vitreous opacities Detachment of the retina Chalazion: Meibomian cyst, tarsal cyst Hordeolum (sty): bacterial inflammation of the sweat gland or gland of Zeiss of an eyelid Conjunctivitis: inflammation of conjunctiva