Download Eyes and Gustation

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
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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
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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