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EYES AND GUSTATION By Kevin Tran, Spencer Ayres, Brandon Shaw, and Morgan Ciehanski VISION We rely on our vision more than any other special sense Visual receptors are located in the eye FUNCTIONS OF ACCESSORY STRUCTURES Protection Lubrication Secretion of tears 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 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 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 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 LACRIMAL APPARATUS Lacrimal Apparatus- produces, distributes, and removes tears Consists of • • • • Lacrimal Gland and associated ducts Lacrimal Canaliculi Lacrimal Sac Nasolacrimal Duct 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 THE EYE Sophisticated visual instruments Contains three distinct layers or tunics • Outer Fibrous Tunic • Middle Vascular Tunic • Inner Neural Tunic (retina) 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 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 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 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 PUPILLARY MUSCLES Pupillary Constrictor Muscles- when it contracts, the pupil decreases (more light) Pupillary Dilator Muscles- contraction enlarges the pupil (less light) 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 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 RODS AND CONES Macula Lutea- has no rods Fovea- contains highest cone concentration Fovea is the site of the sharpest vision STRUCTURE OF THE EYE The eye is hollow Two cavities • Posterior cavity • Anterior cavity is filled with aqueous humor 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 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 ANTERIOR CHAMBER Extends from the cornea to the iris POSTERIOR CHAMBER Extends between the iris and the lens 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 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 TRANSPARENCY Depends on precise combination of structural and biochemical characteristics Lose of balance produces cataracts 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 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 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 FOCAL DISTANCE Focal Distance- distance between the center of the lens and its focal point Determined by two factors 1. 2. Distance from object to the lens Shape of the lens DISTANCE FROM THE OBJECT TO THE LENS The closer an object is to the lens, the greater the focal distance 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 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 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 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 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 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 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 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 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 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 COLOR BLINDNESS People who are unable to distinguish certain colors have a form of color blindness Happens when one or more classes of cones aren't functional Either lack of cones or unable to function properly Most common type is red-green color blindness; red cones are missing so a person cant tell the difference between red and green light EFFECTS OF AGING ON THE EYE Senile cataracts- lens loses transparency, blurred vision Accommodation problems- the near point of vision gradually increases with age EYE DISEASES Conjunctivitis- or pinkeye, due to damage and/or irritation of the conjunctival surface Cataract- balance in the lens becomes disturbed and the lens loses transparency; they can result from injury, radiation, or reaction to drugs, as well as aging Glaucoma- eye disease in which the optic nerve is damaged in a characteristic pattern PROFESSIONS DEALING WITH THE EYE Optometrist- concerned with the health of the eyes and related structures as well as vision, visual systems, etc. ; they are trained to fit lens to improve vision and diagnose and treat diseases of the eye Ophthalmologist- a specialist in medical and surgical eye problems Optician-use prescriptions written by an optometrist or an ophthalmologist to fit and sell eyeglasses, contact lenses and other eyewear TASTE Special sense given to us by the tongue Taste sensation(s) is due to the presence of taste receptors on the tongue TASTE BUDS Made of specialized epithelial cells and taste receptors Contain around 40 cells of different types/stages Basal cells -> Stem Cells in the tongue Gustatory cells -> Mature daughter cells, grow in stages Around 3000 in the adult tongue LINGUAL PAPILLAE Epithelial projections on the tongue Three types: Filiform Papillae, Fungiform Papillae, Circumvallate Papillae Taste Buds located on the papillae FILIFORM PAPILLAE Do not contain taste buds Provide friction to move things around the mouth FUNGIFORM PAPILLAE A contain around five taste buds A little bigger than filiform papillae CIRCUMVALLATE PAPILLAE Can contain up to 100 taste buds Largest of the three types of papillae Forms a “V” at the back of the tongue GUSTATORY DISCRIMINATION Four Primary sensations: Sweet, sour, salty, bitter Two less well known: Umami Umami, Water Different regions of the tongue are more prone to certain tastes than others All sensations have same structure in the taste bud, just slightly different receptor mechanisms Respond much more readily to unpleasant tastes than to pleasant TASTE RECEPTOR UNDERPINNINGS Dissolved chemicals bind to the receptor proteins in gustatory cell Cell releases neurotransmitter, which generates action potential in nervous system AGING ON TASTE With age, the number of functioning taste buds decreases, meaning you’re less sensitive to various tastes Number decreases dramatically after 50 TASTE VIDEO LINK http://bigthink.com/videos/from-tongue-to-brain-the-neurologyof-taste