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Notes:
Special Senses
Chapter 8
Anatomy of the EYE
3
External Eye Structures
• External & Accessory
structures include:
• Eyelids
• Conjunctiva
• Lacrimal apparatus
• Extrinsic eye
muscles
Tendon of levator
palpebrae superioris
Orbicularis
oculi
Eyelid
Eyelash
Cornea
Conjunctiva
4
Eyelids
•Protects the anterior of the eyes
•Eyelashes project from the border of each eyelid
•Tarsal glands on the edges of the eyelids produce an oily
secretion that lubricates the eye
Conjunctiva
• This is a delicate
membrane that lines
the eyelids and covers
a portion of the
eyeball
• Function: secrete
mucus to help
lubricate the eyeball
and keep it moist.
6
Conjunctiva
• Conjunctivitis is due to inflammation of the
conjunctiva. It results in reddened irritated eyes
• Pink Eye is the infection form that is caused by
bacteria or viruses and is highly contagious.
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Lacrimal Apparatus
• Produce a saline
solution, which
washes and lubricates
the eyeball.
• Tears are an increase
in lacrimal secretions
• Makes your nose run
because it drains into
nasal cavity.
Lacrimal gland
Superior and
inferior canaliculi
Lacrimal sac
Nasolacrimal
duct
8
Extrinsic Eye Muscles
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• These are
attached to the
outer surface of
the eye
• Are responsible
for allowing the
eye to follow a
moving object.
Medial Superior
rectus rectus
Superior
oblique
Lateral
rectus
(cut)
Inferior rectus
Inferior oblique
9
Internal Eye Structures
• The eyeball is a hollow sphere.
• Its wall is made of 3 layers or tunics
• The inside is filled with fluids called
humors.
• The lens is the main focusing apparatus and
divides the eye into 2 chambers
10
Structure of the Eye
• Wall has three (3) layers:
• Outer fibrous tunic
• Middle vascular tunic
• Inner sensory tunic
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Lateral rectus
Retina
Ciliary body
Suspensory
ligaments
Choroid coat
Sclera
Vitreous humor
Iris
Lens
Fovea centralis
Pupil
Cornea
Aqueous
humor
Anterior
cavity
Anterior
chamber
Posterior
chamber
Optic nerve
Optic disc
Posterior cavity
Medial rectus
11
Outer Fibrous Tunic
• Consists of the sclera and the cornea.
•The sclera is a thick, glistening white connective tissue.
•Found on the posterior of the eye.
•It is known as the “white of the eye”.
Outer Fibrous Tunic
•The Cornea is located
on the anterior of the eye
•This part is clear and it
is where light enters
•It is the most exposed
part of the eye and
vulnerable to damage,
but it is quick to heal.
Middle Vascular Tunic
• Choroid
• Posterior Portion
• Provides blood supply
• Contains dark pigments
to absorb extra light
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Middle Vascular Tunic
• Ciliary body
• Anterior portion
• Pigmented
• Holds lens
• Moves lens for focusing
Ciliary muscle
fibers contracted
Suspensory
ligaments relaxed
Lens thick
(a)
Ciliary muscle
fibers relaxed
Suspensory
ligaments taut
Lens thin
(b)
Middle Vascular Tunic
Sympathetic
motor nerve
fiber
In dim light
• Iris
• Anterior portion
• Pigmented
• Controls light intensity by
adjusting size of pupil
•Pupil
•The rounded opening in the iris
Radially arranged
Smooth muscle fibers
of the iris
Parasympathetic
ganglion
Circularly arranged
smooth muscle fibers
of the iris
Pupil
In normal light
Parasympathetic
motor nerve fiber
In bright light
Inner Sensory Tunic
• Includes the RETINA that has two layers
• The pigmented layer absorbs extra light.
The cells of the retina also remove dead or
damaged receptor cells. They also help to
store vitamin A that is needed for vision.
Inner Sensory Tunic
• The neural layer of the retina has
photoreceptors that respond to light.
– RODS- allow us to see in dim light and are
responsible for our peripheral vision
– CONES- allow us to see the details of our
world in color and under bright light
conditions.
18
Rods & Cones in Retina
19
Inner Sensory Tunic
• Blind Spot:
– This is the spot where the optic nerve leaves the
eyeball. There are no photoreceptors here so
when light passes over this optic disc the object
dissappears.
20
Inner Sensory Tunic
• Fovea Centralis– A tiny pit that contains only cones. It is the
area of greatest visual acuity or your point of
sharpest vision.
– Center of the retina
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Inner Sensory Tunic
• Lens– Is a flexible biconvex crystal-like structure.
– Held in place by a ligament from the ciliary body.
– It divides the eye into two chambers
• Anterior segment contains a clear watery fluid called
aqueous humor.
• Posterior segment is filled with a gel-like vitreous humor.
• Both help to provide pressure in the eye.
22
Aqueous & Vitreous Humor
Aqueous
Humor
Vitreous humor
Lens
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Cornea
Anterior chamber
Iris
Posterior
chamber
Ciliary process
Suspensory
ligaments
Ciliary muscles
Conjunctiva
Vitreous
humor
Lens
Sclera
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Lens
• LENS
• biconvex: convex
on both sides
• can change shape to
focus
Lens
• AQUEOUS HUMOR
• liquid between cornea and iris
• maintains shape of cornea
• produced by the ciliary body
• VITREOUS HUMOR
• clear, jelly-like liquid inside the
eyeball
• helps maintain spherical shape of
eye
• Presbyopia
• ciliary muscles lose power and the
person becomes farsighted – convex
reading glasses help this
• Colorblindness
• genetic disorder – person missing
cones
• most colorblind people are red-green
colorblind
• Glaucoma
• aqueous humor does not drain
• results in pain and can lead to
blindness as pressure inside eyeball
damages retina
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• Cataracts
• lens becomes cloudy – usually with age
• Cataract Vision
Anatomy of the EAR
31
External Ear (3 parts)
• Auricle (or pinna)– Is what most people call the ear.
– shell-shaped structure that
collects and directs sound waves
into the auditory canal.
External or Outer Ear
• External Acoustic Meatus
(aka the auditory canal)
– Passage to eardrum
– Short, narrow chamber
which secretes earwax to
trap foreign bodies and
repel insects.
External or Outer Ear
• Tympanic Membrane, or eardrum
– Sound waves hit the eardrum causing it to vibrate.
– It separates the external ear from the middle ear.
Middle Ear
• Is an Air-filled space in
temporal bone
•Is connected to the throat by the
eustachian tube.
•This equalizes pressure in
the ear.
•In infants it is very horizontal
so that is why they should not
lay down and drink
•Sore throats in children also
cause middle ear infections
and may need to be
surgically fixed with a tube.
Middle Ear
•Has the 3 smallest bones in the body
called ossicles:
• Vibrate in response to tympanic
membrane
•Hammer, anvil and stirrup
• Oval window
• Opening in wall of tympanic cavity
• Stirrup vibrates against it to move
fluids in inner ear
Inner Ear
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•Made of a bony labyrinth
that is divided into 3 parts:
• Cochlea
• Functions in hearing
• Semicircular canals
• Functions in
equilibrium
• Vestibule
• Functions in
equilibrium
Bony labyrinth
Perilymph
Membranous
labyrinth
Endolymph
Bony labyrinth
(contains perilymph)
Membranous labyrinth
(contains endolymph)
Semicircular
canals
Utricle
Saccule
Vestibular nerve
Cochlear nerve
Scala
vestibuli (cut)
Scala
tympani (cut)
Cochlear
duct (cut)
containing
endolymph
Ampullae Oval Vestibule Round Maculae
window
window
(a)
Cochlea
37
Hearing
38
Mechanism of Hearing
• Sound waves reach the cochlea through
vibrations of the eardrum, ossicles, and oval
window
• This sets the fluid in the inner ear into
motion
• Hair cells in the spiral organ of Corti are
stimulated and transmit impulses to the
cochlear nerve.
39
Animation:
Effect of Sound Waves
on Cochlear Structures
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40
Equilibrium
41
Sense of Equilibrium
• Static equilibrium
• Receptors called maculae are responsible for our static
equilibrium
• Senses position of head when body is not moving
42
Sense of Equilibrium
• Dynamic Equilibrium – balance and movement
• Semicircular canals
• Senses rotation and movement of head and body
Ear Disorders
• Deafness - hearing loss of any kind
• 2 types
1. Conduction Deafness
• something interferes with sound
waves entering the ear
• EX: earwax, ruptured eardrum,
infection
2. Sensorineural Deafness
• damage to receptor cells in
organ of Corti, cochlear nerve, or
neurons
Ear Disorders
• Motion Sickness
• impulses from ear nerves do
not agree with visual input
• can result in dizziness,
nausea, loss of balance
NOTES:
Chemical Senses
46
CHEMORECEPTORS
•Chemoreceptors:
•The receptors for taste and smell are
classified as chemoreceptors because
they respond to chemicals dissolved in
liquids
47
Sense of Smell
48
Sense of Smell
• Olfactory organs
•Are located in a
postage stamped
sized area in the roof
of the nasal cavity.
•Contain olfactory
receptors and
supporting epithelial
cells
The NoseSmelling &
Tasting
• 2 nasal chambers called
nostrils
– Separated by nasal
septum
– Receptors use cilia to
capture smell
• Nose also helps with
taste
• External nose is part
bone and part cartilage
Olfactory Receptors
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Nerve fibers within
the olfactory bulb
Olfactory Olfactory
tract
bulb
Cribriform
plate
Olfactory area of
nasal cavity
Superior nasal
concha
Nasal cavity
Cilia
(a)
Olfactory
Columnar
Cribriform
receptor cells epithelial cells plate
(b)
51
Olfactory Nerve Pathways
• Once olfactory receptors are stimulated, nerve
impulses travel through
• Olfactory nerves
olfactory bulbs
olfactory
tracts
limbic system (for emotions) and olfactory
cortex (for interpretation)
52
Smells and Emotion
• Olfactory impressions are long-lasting and
very much a part of our memories and
emotions.
• There are hospital smells, school smells,
baby smells, travel smells.
• Smells may remind you of specific people
or events.
53
Olfactory Stimulation
•Olfactory receptors are extremely sensitive
and can by activated by just a few molecules.
•Olfactory receptors undergo sensory
adaptation rapidly
• Sense of smell drops by 50% within a second
after stimulation
LAB: SMELL
•
•
•
•
Pick a partner and spread out
Get a beaker, 4 packs of cotton swabs, and 2 oils.
Follow Directions on lab sheet.
Throw away used cotton swabs. Place beakers
and oils back on cart.
• Turn in lab on front table.
• Pick up a review sheet and begin working on it.
55
Sense of Taste
56
Sense of Taste
• Taste buds
• Organs of taste
• Located on papillae of tongue, roof of
mouth, linings of cheeks and walls of
pharynx
• Papillae are small peg-like projections
on the dorsal surface of the tongue.
•Get replaced every 7-10 days
Sense of Taste
• Taste receptors
• Taste cells – modified epithelial cells that
function as receptors
• Taste hairs –microvilli that protrude from
taste cells; sensitive parts of taste cells
Taste Receptors
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Papillae
Taste buds
Epithelium
of tongue
Taste cell
(a)
Taste hair
Supporting
cell
Taste
pore
(b)
Connective
tissue
Sensory
nerve fibers
59
Taste Nerve Pathways
• Sensory impulses from taste receptors travel along:
• Cranial nerves to…
• Medulla oblongata to…
• Thalamus to…
• Gustatory cortex (for interpretation)
60
Taste Sensations
• Five primary taste sensations
• Sweet – stimulated by carbohydrates
• Sour – stimulated by acids
• Salty – stimulated by salts
• Bitter – stimulated by many organic
compounds
•Umami- (means delicious in japan)
detects beef taste or proteins