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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.

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Eyes and gustation

Eyes and Gustation

By Kevin Tran, Spencer Ayres, Brandon Shaw, and Morgan Ciehanski


  • We rely on our vision more than any other special sense

  • Visual receptors are located in the eye

Functions of accessory structures
Functions of accessory structures

  • Protection

  • Lubrication

  • Secretion of tears

Accessory structures of the eye
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


  • 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 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
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

  • Lacrimal Apparatus- produces, distributes, and removes tears

  • Consists of

    • Lacrimal Gland and associated ducts

    • Lacrimal Canaliculi

    • Lacrimal Sac

    • Nasolacrimal Duct

Lacrimal apparatus1
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
The eye

  • Sophisticated visual instruments

  • Contains three distinct layers or tunics

    • Outer Fibrous Tunic

    • Middle Vascular Tunic

    • Inner Neural Tunic (retina)

Fibrous tunic
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
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 tunic1
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

Eyes and gustation

  • 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 muscles

  • Pupillary Constrictor Muscles- when it contracts, the pupil decreases (more light)

  • Pupillary Dilator Muscles- contraction enlarges the pupil (less light)

Neural tunic
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
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
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
Structure of the eye

  • The eye is hollow

  • Two cavities

    • Posterior cavity

    • Anterior cavity is filled with aqueous humor

Posterior cavity
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
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
Anterior chamber

  • Extends from the cornea to the iris

Posterior chamber
Posterior chamber

  • Extends between the iris and the lens

Eyes and gustation

  • 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
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


  • Depends on precise combination of structural and biochemical characteristics

  • Lose of balance produces cataracts


  • 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


  • 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
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

  • 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

Distance from the object to 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 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- 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


  • 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


  • 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
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

  • 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


  • 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


  • 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
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
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
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
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
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
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


  • Special sense given to us by the tongue

  • Taste sensation(s) is due to the presence of taste receptors on the tongue

Taste buds
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
Lingual papillae

  • Epithelial projections on the tongue

  • Three types: Filiform Papillae, Fungiform Papillae, Circumvallate Papillae

  • Taste Buds located on the papillae

Filiform papillae
Filiform papillae

  • Do not contain taste buds

  • Provide friction to move things around the mouth

Fungiform papillae
Fungiform papillae

  • A contain around five taste buds

  • A little bigger than filiform papillae

Circumvallate 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
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
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
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
Taste video link

  • http://bigthink.com/videos/from-tongue-to-brain-the-neurology-of-taste