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Special Senses
Chapter 8
 The
special senses are touch, taste, smell,
sight, and hearing.
 Equilibrium is also considered a sense of
balance.
 The eye and vision - Visual stimuli makes
up 70% of sensory receptors in the body.
Anatomy of the eye

A. External Structures
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a. Eyelids - meet medially/laterally for protection
b. Eyelashes - protection from each eyelid
c. Meibomian glands - oily lubricant
d. Ciliary glands - sweat glands between the
eyelashes
e. Conjuctiva - lining of the eyelid and eyeball (PINK
EYE - inflammation of eye - conjunctivitis)
f. Lacrimal glands - release salty tears to flush
eyeball and destroy bacteria
g. External eye muscles - produce gross eye
movements
Anatomy of the eye
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B. Internal Structures
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a. Eyeball - fluid-filled (humors) hollow sphere
b. Sclera - a thick white protective tissue (white of the
eye)
c. Cornea - transparent covering for the eye that contains
various nerve endings
d. Choroid layer - a blood-rich covering that contains
dark pigment
e. Ciliary body - attaches to the lens to help it change
shape
f. Lens - magnifies the object
g. Iris - colored pad of the eye
h. Pupil - opening through which light passes (dilates and
constricts)
Anatomy of the eye
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B. Internal Structures, continued….
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i. Retina - the back lining of the eye
j. Rods - black and white receptors on the retina (night
vision)
k. Cones - color receptors on the retina (X-linked)
l. Optic nerve - a nerve that is connected to the brain
m. Blind spot - the spot where the optic nerve leaves the
eyeball
N. Fovea centrally - lateral to the blind spot/contains a lot
of Cones
O. aqueous humor - clear watery fluid
p. Vitreous humor - reinforces the eyeball and gives it
structure ("snot")
q. Fundus - healthy posterior wall of the eye
EYE PROBLEMS

1) Night blindness - abnormal rods that hinder our ability to
see at night
 2) Color blindness - lack of one or more types of cones (color
receptors) - X-linked trait
 3) Cataracts - the soft gel-like structure becomes foggy and
impairs vision "bright sunlight''
 4) Glaucoma - drainage is blocked and pressure builds up in
the eye
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a. Halos around light
b. Headaches
c. Blurred vision
d. Often caused by smoking. Light passing through the eye can be a
different medium (water to air). The image (upside down) refracted as it
passes through the retina. Humans have binocular vision (two-eyed have
optical tracts that meet at a fixation point) where both eyes point
Photopupillary Reflex - protective reflex to changes in bright light
(Constriction of pupils - bright light, dilation of pupils - dark light)
Problems of Refraction
THE EAR - Hearing and Balance
 Fluids
must be moved to stimulate the
hearing receptors.
 Sound vibrations move the fluid to
stimulate receptors.
 Mechanoreceptors respond to physical
forces that allow us to range our hearing
from about 20-20,000 hertz.
 Our equilibrium is also in the inner ear and
helps us to maintain balance.
EAR ANATOMY
 OUTER
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EAR
1) Pinna - the actual cartilaginous earlobe
2) external auditory canal - long narrow
chamber (1 inch long) that goes by the
temporal bone
3) ceruminous glands - skin lined wax
producing glands (ear wax)
4) tympanic membrane - "eardrum" - receiver
for sound vibrations
EAR ANATOMY
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MIDDLE EAR
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1 ) tympanic cavity- small air-filled cavity
2) oval window/round window - membrane opening
3) auditory tube - links middle ear with the throat
• a. sore throat can lead to ear infections
• b. yawning, chewing gum, swallowing can relieve pressure in
the ear
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4) ossicles - bones of the middle ear
• a. hammer (malleus)
• b. anvil (incus)
• c. stirrup (stapes)
 Middle
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Ear Problems:
Otitus Media - the eardrum bulges and is
inflamed. Large amounts of pus or fluid can
accumulate and surgery (lancing the eardrum)
to relieve the pressure. Tubes are put in to
help drainage.
EAR ANATOMY
 INNER
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EAR
The inner ear has bony chambers called osseous
or bony labyrinth.
1) Osseous - bony chambers
• a. Cochlea - snail shaped structure that holds fluid
• b. Vestibule - located between cochlea and
semicircular canals. The connection point of the
vestibulochlear nerve.
• c. Semicircular canals - balance of fluid motion The
bony labyrinth is filled with plasmalike fluid called
perilymph and thicker fluid called endolymph.
Inner Ear
EQUILIBRIUM
 Your
equilibrium responds to certain
movements of the head.
 The equilibrium receptors of the inner ear
are sometimes called vestibular apparatus
can be static or dynamic equilibrium.
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HOW DO WE HEAR??
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Mechanisms of Hearing:
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Within the cochlea, the organ of Corti contains hearing
receptors (hair cells) that allow us to hear.
Sound waves reach the cochlea through vibrations of the
eardrum, ossicles (bones of the middle ear), oval window,
and movement of fluid in the inner ear.
The force of the bones in the middle ear set the fluid in
motion.
The hair cells of the Organ of Corti are set into motion by
beating with the vibrations.
These vibrations are transmitted along the cochlear nerve.
Excitation of Hair Cells in the Organ of Corti
Figure 15.28c
Hearing Defects
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1) Deafness - loss of or total inability to hear sounds
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a. Conduction - interference of sound waves by otitus media,
fusion of the ossicles, and buildup of ear wax.
b. Sensorimental deafness - degeneration or damage of the
receptor cells
2) Equilibrium - nausea, dizziness, and problems
maintaining balance
 3) Meniere's syndrome - symptoms are nausea,
vertigo, and they are prescribed motion sickness
drugs.
Chemical Senses
senses – gustation (taste) and
olfaction (smell) Smell and taste compliment
each other and have a wider range of
sensitivity.
 Their chemoreceptors respond to chemicals
in aqueous solution
 Chemical
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Taste – to substances dissolved in saliva
Smell – to substances dissolved in fluids of the
nasal membranes
Taste Buds
 Most
of the 10,000 or so taste buds are
found on the tongue
 Taste buds are found in papillae of the
tongue mucosa
 Papillae come in three types: filiform,
fungiform, and circumvallate
 Fungiform and circumvallate papillae
contain taste buds
Taste Buds
Anatomy of a Taste Bud
 Each
gourd-shaped taste bud consists of
three major cell types
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Supporting cells – insulate the receptor
Basal cells – dynamic stem cells
Gustatory cells – taste cells
Taste Sensations
 There
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are five basic taste sensations
Sweet – sugars, saccharin, alcohol, and some
amino acids
Salt – metal ions
Sour – hydrogen ions
Bitter – alkaloids such as quinine and nicotine
Umami – elicited by the amino acid glutamate
Physiology of Taste
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order to be tasted, a chemical:
Must be dissolved in saliva
Must contact gustatory hairs
 Binding
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of the food chemical:
Depolarizes the taste cell membrane, releasing
neurotransmitter
Initiates a generator potential that elicits an action
potential
Influence of Other Sensations on
Taste
 Taste
is 80% smell
 Thermoreceptors, mechanoreceptors,
nociceptors also influence tastes
 Temperature and texture enhance or
detract from taste
Sense of Smell
 The
organ of smell is the olfactory
epithelium, which covers the superior
nasal concha
 Olfactory receptor cells are bipolar
neurons with radiating olfactory cilia
 Olfactory receptors are surrounded and
cushioned by supporting cells
 Basal cells lie at the base of the epithelium
OLFACTORY SPECIAL SENSES
 1)
Olfactory receptors - are located at the
roof of each nasal caviler so sniffing and
smelling intensifies the smell receptors
 2) Olfactory hairs - neurons on long cilia that
stick out from the nasal epithelium and are
bathed by a layer of clear mucus.
 3) Olfactory nerve - connected to the
olfactory part of the brain.
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Olfactory becomes a part of our memory
EX: Mom's cooking
Special Senses: Problems
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1 ) Strabismus - ''crossed eyes'' - caused by
weak eye muscles.
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Correction: surgery, eye exercises
2) Rubella - ''German Measles'' - congenital
blindness Correction: vaccination/MMR
 3) Gonorrhea - baby's eyes are infected with
bacteria
 4) Conjunctivitis - ''pink eye'' - eyes are red,
swollen, and produce pus
 5) Presbyopia - ''old age vision'' - the
decreasing of lens elasticity