Eyes and Gustation

1. Eyes and Gustation By Kevin Tran, Spencer Ayres, Brandon Shaw, and Morgan Ciehanski

2. Vision • We rely on our vision more than any other special sense • Visual receptors are located in the eye

3. Functions of accessory structures • Protection • Lubrication • Secretion of tears

4. Accessory structures of the eye • Superficial Epithelium of the Eye- thin layers of skin around the eye and covering the eye itself • Eyelashes- robust hairs that help prevent foreign materials from reaching the eye • Eyelids – continuation of the skin that protect and lubricate the eye

6. eyelashes • Located along the inner margin of the eye lid • Tarsal Glands- also known as Meibomian, are modified sebaceous glands • Tarsal glands secrete lipid-rich products that keep the eye lids from sticking together

7. Eyelids • Eyelids open and close eye using muscles fibers • Orbicularis Oculi and Levator Palpebrae Superioris muscles are responsible for closing the eye and raising the upper lid

8. Epithelium of the eye • Conjunctiva- outer surface of the eye that a mucous membrane covered in stratified squamous epithelium • Palpebral Conjunctiva- inner surface of the eyelid • Ocular Conjunctiva- the anterior surface of the eye • Cornea- a transparent part of the outer fibrous layer

9. Lacrimal apparatus • Lacrimal Apparatus- produces, distributes, and removes tears • Consists of • Lacrimal Gland and associated ducts • Lacrimal Canaliculi • Lacrimal Sac • Nasolacrimal Duct

10. Lacrimal apparatus • Lacrimal Gland- tear gland • Lacrimal Canaliculi- small canals that lead to the lacrimal sac • Lacrimal Sac-holds the tears that the lacrimal gland produces • Nasolacrimal Duct- delivers tears to the nasal cavity on that side

11. The eye • Sophisticated visual instruments • Contains three distinct layers or tunics • Outer Fibrous Tunic • Middle Vascular Tunic • Inner Neural Tunic (retina)

12. Fibrous tunic • Outermost layer • Consists of sclera and cornea • Sclera- “white of the eye”; made of collagen and elastic fibers • Provides mechanical support and some physical protection • Serves as an attachment site for the eye muscles • Contains structures that assist in the focusing process

13. Vascular tunic • Also known as the Uvea • Contains blood vessels, lymphatic vessels, and the intrinsic muscles of the eye • Provides a route for blood vessels and lymphatics that supply tissues of the eye • Regulating the amount of light the eye receives

14. Vascular tunic • Secreting and reabsorbing the aqueous humor that circulates the eye • Controls the shape of the lens • Contains the iris • Visual receptors, or Photoreceptors, located in neural tunic

15. Iris • Iris- visible through the corneal surface, contains the blood vessels, pigment cells, and smooth muscle fibers • Pupillary muscles- muscles that contract and changes the diameter of the pupil • Pupil- central opening of the iris

16. Pupillary muscles • Pupillary Constrictor Muscles- when it contracts, the pupil decreases (more light) • Pupillary Dilator Muscles- contraction enlarges the pupil (less light)

18. Neural Tunic • Also known as the Retina • Retina helps process visual information • Contains two parts: pigmented part and neural part • Pigmented part absorbs light • Neural part is in control of processing • Also contains photoreceptors • Photoreceptors- cells that detect light

19. Organization of retina • Rods and cones • Rods- highly sensitive to light, don’t ‘see’ colors • Cones- ‘sees’ colors, provide sharper clearer images • Optic Nerve- transmits the visual images picked up from the rods and cones and delivers them to the brain

20. Rods and cones • Macula Lutea- has no rods • Fovea- contains highest cone concentration • Fovea is the site of the sharpest vision

21. Structure of the eye • The eye is hollow • Two cavities • Posterior cavity • Anterior cavity is filled with aqueous humor

23. Posterior cavity • Or Vitreous Chamber, contains the vitreous body • Vitreous Body- or Vitreous Humor, gelatinous substance that makes up most of the volume of the posterior cavity • Helps stabilize the shape of the eye

24. Anterior Cavity • Divided into two chambers • Anterior chamber • Posterior chambers • Chambers are filled with Aqueous Humor • Aqueous Humor- fluid that circulates within the anterior cavity, passing through the chambers of the pupil

25. Anterior chamber • Extends from the cornea to the iris

26. Posterior chamber • Extends between the iris and the lens

28. lens • Lies posterior to the cornea • Primary function is to focus the visual image on the photoreceptors • Focus happens by the change in shape of the lens • Lens fibers are in the interior of the lens

30. Lens fibers • Lost their nucleus and organelles • Slender and elongated • Filled with transparent proteins called crystallins • Crystallins- responsible for clarity and focusing power of the lens

31. transparency • Depends on precise combination of structural and biochemical characteristics • Lose of balance produces cataracts

32. refraction • The light that is collected by the photoreceptors in refracted, or bent when passing from one medium to another • Pencil in water • Refraction occurs when passing light through the cornea and then into the lens

33. refraction • Greatest amount of refraction occurs when light passes through the air into the corneal tissues • Tissues have a density similar to water • When you opne your eyes underwater you cant see as easily because the air-water refraction has been eliminated and replaced with water to water, thus light remains unbent and

34. Additional refraction • Light passes through the aqueous humor into the dense lens • This lens provides extra refraction that’s needed to focus the light rays from an object to a focal point • Focal Point- a specific point of intersection of the retina

35. Focal distance • Focal Distance- distance between the center of the lens and its focal point • Determined by two factors • Distance from object to the lens • Shape of the lens

36. Distance from the object to the lens • The closer an object is to the lens, the greater the focal distance

37. The shape of the lens • The rounder the lens the more refraction occurs, so a very round lens has a shorter focal distance than a flatter one

39. accommodation • Accommodation- focusing images on the retina by changing the shape of the lens to keep the focal length constant • To view nearby objects the lens becomes rounder • The lens flattens when we view a distant object • Lens are held in place by suspensory ligaments

40. accommodation • Greatest amount of refraction is needed for viewing objects up close • Inner limit of clear vision is called the near point of vision • Children can see things up close but as time goes on the lens becomes stiffer and less responsive • Aging effects the near point of vision

42. Astigmatism • If light doesn’t pass properly the image is distorted • Astigmatism- the degree of curvature in the cornea or lens varies from one axis to another • Image distortion may be so minimal people don’t even notice the condition

43. Image reversal • Light originates at a single point either near or far • However and object in view is a complex light source that is treated as a large number of individual points • These individual points creates a miniature image of the original but is upside down and backwards • The brains compensates for this image reversal and we don’t notice it

45. Visual activity • Visual activity- clarity of vision • Rated against a ‘normal’ standard (20/20, 20/15, etc.) • Considered legally blind when vision falls below 20/200, even with glasses or contact lenses

46. blindness • Terms implies a total absence of vision due to damage of the optic pathways • Common causes are • Diabetes mellitus • Cataracts • Glaucoma • Corneal scarring • Detachment of the retina • Hereditary factors

47. Scotomas • Abnormal blind spots that may appear in the field of vision • Permanent in a fixed position • Result from a compression of the optic nerve, damage to the photoreceptors, of damage to the visual pathway • Also Floaters, which a small spots that drift across the field of vision, generally temporary phenomena

48. Color vision • Objects appear to have color if they reflect or transmit photons from one portion of the visible spectrum and absorbs the rest • Photons stimulate rods and cones • Photons of all colors bounce off an object or rods themselves are stimulated, the object will appear white • If photons are absorbed by the object (none reach the retina), the object appears black

49. Cone types • Blue cones, green cones, and red cones • Each have a sensitivity to a different range of wavelengths • Stimulation to different combos of wavelength creates color vision • Color discrimination results from the integration of info from all three types of cones • EXAMPLE: Yellow is formed from a combo of highly stimulate green cones, less strongly stimulated red cones, and relatively unaffected blue cones