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Exercise 17
Special Senses
Portland Community College
BI 232
Special Senses
• Sensory receptors are extensions of the
nervous system
• Contain specialized cells or processes that
relay specific information
• A receptor must convert the stimulus to an
action potential (transductions)
• The AP must be conducted from the
receptor to the CNS
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General and Special senses
• General senses include
touch, pressure, vibration,
pain, temperature,
proprioception and
chemical and fluid
pressure.
• Special senses include
olfaction, gustation, vision
and hearing and
equilibrium
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Olfaction
• Sensory receptors for
olfaction are located in
the olfactory
epithelium consists of:
• Olfactory receptor
cells
• Supporting cells
• Basal cells
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Testing olfactory adaptation
• Adaptation refers to a
decreasing sensitivity
to a stimulus over
time.
• Sensitivity to an odor
diminishes over time.
• Do Activity 17.2
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Gustation
• Sensory receptors for
gustation are located
in taste buds
• Located mainly on the
top of the tongue but
also in other areas of
mouth
• Innervated by cranial
nerves VII, IX and X
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Lingual Papilla
• Papilla are epithelial projections on the
superior surface of the tongue
• Circumvallate papilla contain about 100
taste buds
• Fungiform papilla contain about 5 -10 taste
buds
• Filiform papillae provide friction that helps
the tongue move objects around in the
mouth, but do not contain taste buds
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Taste Receptors
• Taste buds contain spindle-shaped cells
• Basal cells: produce daughter cells that
mature in stages
• Gustatory cells: extend microvilli into the
surrounding fluids through a taste pore
• Contain the taste receptors
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Taste
Bud
Histology
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Gustatory Discrimination
1.
2.
3.
4.
5.
•
•
Umami: “Beef”
Salty
Sweet
Bitter
Sour
Substances must be dissolved (saliva) for
the chemically gated ion channels to open
Olfaction is very important in taste
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Lab Activities
• Look at the modes that
show oral structures
• Look at slides of taste
buds.
• Do activity 17.4: Parts
A and B
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Lab Activity 17
Vision
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Histology of the Retina
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Ciliary body
A
1. Ciliary processes
• Ciliary epithelium
• Secretes aqueous humor
2. Ciliary muscle
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P
- (intrinsic eye muscle)
3. Suspensory ligament of the lens
A= anterior chamber
P= posterior chamber
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2
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Neural pathway for vision
• After optic nerves exit the
eyeballs they meet at the
optic chiasm.
• Fibers from medial half of
retina cross over to the
opposite side.
• Optic tracts project to the
lateral geniculate bodies
in thalamus
• Some fibers are relayed to
superior colliculi
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Lacrimal Apparatus
• Consists of the
lacrimal gland and its
accessory structures.
• Produces water,
alkaline tears.
• Contain antibacterial
enzyme called
lysozyme for
protection from
bacterial infections
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Extrinsic Eye Muscles
• Superior oblique: primarily rotates the top of
the eye toward the nose and secondarily moves
the eye downward
• Trochlea: Ligament sling
• Superior rectus: primarily moves the eye
upward and secondarily rotates the top of the
eye toward the nose
• Lateral rectus: moves the eye away from the
nose
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Extrinsic Eye Muscles
• Medial rectus: moves the eye toward the
nose
• Inferior oblique: primarily rotates the top of
the eye away from the nose and secondarily
moves the eye upward
• Inferior rectus: primarily moves the eye
downward and secondarily rotates the top of
the eye away from the nose
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Ear
Nose
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Extrinsic Eye Muscles
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Refraction
• Light is bent when it passes from one
medium to another medium with a different
density
• Light passes through these before it hits the
retina:
•
•
•
•
Cornea
Aqueous humor
Lens
Vitreous humor
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Focal Point & Focal Distance
•
•
Focal Point: The specific point of
intersection on the retina.
Focal distance: The distance between the
center of the lens and its focal point.
Determined by two factors:
1. Distance from the object to the lens
2. Shape of the lens
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Focal Distance
•
•
Distance from the object to the lens: the closer an
object is, the greater the focal distance
Shape of the lens: the rounder the lens, the more
refraction occurs, so it has a shorter focal distance
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Accommodation
• Accommodation is an alteration in the curvature of
the lens of the eye to focus an image on the retina
• Near objects: Lens becomes rounder
• Distance objects: Lens becomes flatter
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Accommodation
• Emmetropia is
normal vision.
• The image will be
focused on the
retina’s surface
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Accommodation Problems
• Myopia: Nearsighted
• The eyeball is too deep or
the curvature of the lens is
too great
• The focal point is in front of
the retina, so distance
objects are blurry
• Corrected with a diverging
lens
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Accommodation Problems
• Hyperopia: Farsighted
• The eyeball is too shallow or
the curvature of the lens is too
flat
• The focal point is behind of the
retina, so near objects are blurry
• Corrected with a converging
lens
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Astigmatism
• The degree of curvature
in the cornea or lens
varies from one axis to
another (is uneven or wavy)
• This causes light to focus on more than one
area of the retina creating a blurry image.
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Intrinsic Eye Muscles of the
Iris

Pupils constrict (Parasympathetic)


Close vision and bright light
Pupils dilate (Sympathetic)

Distant vision and dim light
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Color Blindness
• Cones are responsible
for color vision.
• 3 types of cones each
able to absorb light at
specific wavelengths.
• Lack of one or more
types of cone can
cause color blindness
• Use Ishihara color
plates to test
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Activities
• Dissect cow eye
• Perform visual tests
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Lab Activity 18
Hearing & Equilibrium
Vestibular Portion
Cochlear Portion
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Middle Ear Ossicles (Bones)
Malleus
Incus
Stapes
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• The stapes strikes
the oval window of
the cochlea
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Vestibular Complex
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Cochlea
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Cochlea Uncoiled
oval
window
round
window
•
•
•
•
vestibular duct
helicotrema
tympanic duct
Cochlear duct
containing the
Organ of Corti
Stapes pushes on fluid of vestibular duct at oval window
At helicotrema, vibration moves into tympanic duct
Fluid vibration dissipated at round window which bulges
The central structure is vibrated (cochlear duct)
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Organ of
Corti
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Neural pathways for hearing
• Vestibulocochlear
nerve (CN VIII) has 2
divisions:
• Vestibular divisionsend impulses to
medulla where fibers
are crossed and
uncrossed to travel to
the cerebellum; to the
cortex
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Neural pathways for hearing
• The cochlear division
receive impulses to the
cochlear nuclei in the
medulla.
• Some fibers cross over to
other side.
• Some remain on the same
side.
• Both synapse in the
inferior colliculi
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Types of Hearing Loss
• Conductive hearing loss occurs when sound is not
conducted efficiently through the outer ear canal
to the eardrum and the bones of the middle ear.
• Sensorineural hearing loss occurs when there is
damage to the inner ear (cochlea) or to the nerve
pathways from the inner ear to the brain.
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Weber & Rinne Tests
• Weber test: determines if hearing loss is
present in one ear, but does not distinguish
conductive and sensorineural deafness
• Rinne test : Evaluates an individual’s ability
to hear sounds conducted by air or bone
• Used together, these test can distinguish
between the two types of hearing loss
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Weber Test
• Ring tuning fork and place on
center of head. Ask the subject
where they hear the sound.
• Interpreting the test:
• Normally, the sound is heard in the
center of the head or equally in
both ears.
• Sound localizes toward the poor ear
with a conductive loss
• Sound localizes toward the good
ear with a sensorineural hearing
loss
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Rinne Test
• Place the vibrating tuning fork on
the base of the mastoid bone.
• Ask patient to tell you when the
sound is no longer heard.
• Immediately move the tuning fork
to the front of the ear
• Ask the patient to tell you when
the sound is no longer heard.
• Repeat the process putting the
tuning fork in front of the ear first
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Rinne Test
• Normally, someone will hear the
vibration in the air (in front of the ear)
after they stop hearing it on the bone
• Conductive hearing loss: If the person
hears the vibration on the bone after
they no longer hear it in the air.
• Do Activity 17.8
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The End
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