Special Senses
Utilize distinct receptor cells
as receptors
Chemical senses
Taste
(gustation)
Smell (olfaction)
Taste
Taste
buds.
• Most are on the tongue.
• Papillae.
–Filiform - rough, conical shape, few
taste buds
–Fungiform – scattered; most
numerous on sides and tips
–Circumvallate –largest; least
numerous; back of tongue
Structure of a taste bud.
cells – form bulk, insulate
Receptor (Gustatory or Taste) cells –
contain gustatory hairs that extend
through surface
Basal cells - stem cells that divide
giving rise to new gustatory cells
Supporting
Taste sensation
– stimulated by acids
Sweet – stimulated by sugars,
alcohols, some amino acids
Bitter – stimulated by bases
Salty – stimulated by metal ions
Sour
Sensitivity of the taste buds in
different locations.
Anterior
tongue is more sensitive to
sweet and salty substances
Posterior tongue is more sensitive to
bitter substances.
Lateral tongue is more sensitive to
sour substances.
Physiology of taste.
Chemical
comes in contact with gustatory
hair cells on receptor cells.
Depolarization of taste cells results in
generation of action potentials in
associated sensory neurons.
Relayed to the gustatory cortex.
Other sensations
• Taste is 80% smell
• Affected by temperature; texture; heat
Smell
Localization
and structure of
olfactory receptors
Detects chemicals in solution
Olfactory epithelium - Contains the
olfactory receptors and is located in
the roof of the nasal cavity.
Structure of olfactory
receptors.
cells –
Basal cells –
Olfactory receptor cells –
Supporting
Specificity of the olfactory
receptors –
Can
distinguish 10,000 chemicals
Not clearly understood
May be 1000 odorant binding proteins
that act in combinations
Activation of olfactory receptors.
Chemical
comes in contact with the
olfactory hair cells on the receptor cells.
Depolarization of the receptor cells
results in the generation of action
potentials.
Homeostatic imbalances of the
chemical senses
– without smell
Uncinate fits – temporary distortions
of smell due to brain damage,
psychological disorders, or even
seizures
Anosmias
Vision
Accessory
structures of the eye
• Eyebrows
• Eyelids “palpebrae”
–Canthi – angles of the eyelids
–Epicanthic fold – found in Asians
–Lacrimal Caruncle – fleshy elevation
found at medial canthus
• Meibomian glands – Modified
sebaceous glands in eyelid
• Infection of these called Chalazion
• Ciliary glands – between hair
follicles of eyelashes
• Infection of these called a Sty
• Conjunctiva – mucus membrane
covering eye (infection called
conjunctivitis or pinkeye
Accessory Structures of Eye
Lacrimal
apparatus
• Lacrimal glands – secrete
tears
• Lacrimal secretions –
contains mucus,
antibodies, & lysosozyme
–Cleanses, protects, &
lubricates eye
Extrinsic eye muscles
rectus –
Superior rectus Lateral rectus Inferior rectus Superior oblique Inferior oblique –
Medial
Structures of the eyeball
Fibrous tunic (coat) – outermost layer
–Sclera – whites of the eye
–Cornea – clear portion in front of
eye
Vascular tunic (coat) – middle layer (uvea)
–Choroid – vascular brown membrane
–Ciliary body – encircles lens forming the:
• Ciliary muscles – control lens shape
• Ciliary processes - contain capillaries
that secrete fluid
• Suspensory ligaments –
–Iris – colored portion
–Pupil – opening in iris
Sensory tunic (Retina) – innermost
layer
–Pigmented layer – absorbs light
–Neural layer – contains photorecptor cells
–Cells of the retina.
• Ganglionic cells – generate action
potentials
• Bipolar cells – transfer energy from
receptors to ganglionic cells
• Photoreceptors - sensitive to light
• Rods – dim-light, no color, and peripheral
vision
• Cones – bright light, color vision
• Macula lutea – “yellow spot” directly behind
pupil
• Fovea centralis – minute pit in center of
macula lutea
• Contains cones only
• Macular degeneration - linked to nutritional
deficiencies
• Optic disc (blindspot) – location of junction
with optic nerve
Internal chambers and fluids
Posterior
segment - behind lens
• Vitreous humor - clear gel

Anterior segment - in front of
lens
–Anterior chamber - in front of iris
–Posterior chamber - between iris and
lens
–Aqueous humor - clear liquid
filling anterior segment
–Scleral venous sinus (Canal of
Schlemm) - drains aqueous humor
back into veins; located at corneal
/ scleral junction
–Glaucoma - elevated pressure of
the aqueous humor
Lens
Biconvex;
transparent; held in place by
suspensory ligaments
Lens epithelium - outer covering
Lens fibers - inner bulk of lens
• made of folded proteins called crystallins
Cataracts - clouding of the lens
• Age related hardening and thickening;
diabetes; inadequate delivery of nutrition to
lens
Physiology of vision
Photons
- packets of light
Wavelength
• Electromagnetic spectrum - all wavelengths
• Visible spectrum - 400-700 nanometers
–nanometer = 1 billionth of a meter
• Color - reflection of different wavelengths
–Red, Orange, Yellow, Green, Blue, Indigo,
Violet
Refraction and lenses
Reflection
- light bounces off a surface
Refraction - light bends as it passes
through one substance to another with a
different density
Lens - a transparent material curved at
one or both surfaces
• Convex - thicker in the center; light
converges
• Concave - thicker at the edges; light spreads
Focusing of light on the retina.
• Light is refracted three times
–Cornea
–Entering the lens
–Exiting the lens
Focusing for distance vision.
Eye
are fixed (preset) on an object
20 feet or more away.
Ciliary muscles are completely
relaxed.
Lens is stretched as thin as it can get.
Focusing for close vision.
Accommodation
of the lens.
–Ciliary muscles contract.
–Lens bulges.
Constriction
of the pupils Convergence of the eyeballs -
Homeostatic imbalances of refraction.
Myopia
- Nearsightedness
• Eyeball is too long
• Image is focused in front of retina
Hyperopia
- Farsightedness
• Eyeball is too short
• Image is focused behind the retina
Astigmatism
- caused by unequal
curvature in different parts of the lens
Photoreception.
Functional
anatomy of the
photoreceptors
• Outer segment.
• Inner segment
The chemistry of visual pigments.
Retinal
- a light absorbing pigment
• made from vitamin A
• combines with opsonins forming
–Rhodopsin - “purple” visual pigment of Rods
–Light stimulation separates retinal from the
opsins
–Retinal will be re-joined with the opsins to
regenerate rhodopsin later
Different types of opsins in cones.
3
Different types of Cones
• Blue - absorbs blue wavelengths best
• Green - absorbs green wavelengths best
• Red - absorbs red wavelengths best
Cone
wavelengths overlap
Stimulation of various cones in different
amounts creates different shading and
coloration
Color blindness Sex-linked,
genetic trait
Lack specific types of cones,
usually red or green
Light transduction in photoreceptors.
Generation
of electrical current
Photoreceptors depolarize in dark and
hyperpolarize in light
Produce graded potentials (local)
Action potentials produced by Ganglion
cells
Light and dark adaptation Light
adaptation - from dark to light
(5-10 minutes)
Dark adaptation - from light to dark
(20-30 minutes)
Binocular vision and stereopsis
Anterior
placement of eyes
results in greater depth
perception or three-dimensional
vision
Hearing and balance
Structure
of the ear
• Outer (External) ear.
–Auricle (pinna)
–External auditory canal (meatus)
• Ceruminous glands - wax glands
–Tympanic membrane - “eardrum”
• boundary between outer and middle ear
Middle ear (Tympanic cavity)
Mastoid
antrum - canal leading to mastoid
process
Pharyngotympanic (auditory or eustachian)
tube - equalizes pressure on eardrum
Ear ossicles.
• Malleus (hammer) • Incus (anvil) • Stapes (stirrup) • Ear muscles: Tensor tympani & Stapedius
Inner (Internal) ear
Bony
(Osseous) labyrinth.
• Cochlea - “snail” ; hearing
• Semicircular canals - balance
• Vestibule - central cavity
Membranous
labyrinth.
• Perilymph - surrounds membrane
structures
• Endolymph - fills membrane structures
Vestibule
Saccule
- smaller sac nearer
cochlea
Utricle - larger sac nearer
semicircular canals
Maculae - receptors for balance
and head position
Semicircular canals. anterior, posterior,
lateral
Semicircular
ducts - connect
canals to utricle
Ampulla - swollen base of
canals; houses:
• Crista ampullaris - receptors for
head movement
Mechanisms of equilibrium
 Static
equilibrium = head position
 Maculae - receptors for static equilibrium
• Supporting cells contain hair cells embedded in
gel-like otolithic membrane
–Otoliths -crystals that make membrane heavier,
increase inertia
–Utricle’s macula is horizontal for linear
acceleration stimuli –Saccule’s macula is vertical and responds to
vertical movements
Dynamic equilibrium.
Crista
ampullaris -- located in the
ampulla
• Supporting cells • Hair cells • Cupula - gelled mass resembling a
pointed cap
Responds
to rotational stimuli -
Cochlea.
Modiolus
-
• bony pillar at center
Cochlear
duct -
• wedge-shaped duct
containing Organ of
Corti
• Organ of Corti receptor for hearing
Scalas “chambers”
• Scala vestibuli - connects to vestibule at
oval window
• Scala media = cochlear duct
• Scala tympani - connects to vestibule at
round window
Vestibular membrane - roof of cochlear
duct
Basilar membrane - floor of cochlear duct
Sound and mechanisms of hearing
Properties
of sound.
• Frequency - measured in hertz
• Amplitude - measured in decibels (dB) –logarithmic (exponents of ten)
–0 dB = hearing threshold
–50 dB = normal conversation
–90 dB = danger zone
–120 dB = Rock concert
–130 dB = Pain threshold
Transmission of sound to the inner ear Vibrations
transferred from air to
tympanic membrane to malleus, incus,
stapes, to oval window, to cochlear fluid
causing resonance of the basilar
membrane Basilar membrane contains fibers of
different lengths that resonate to different
frequencies from high to low
Excitation of hair cells in the organ
of Corti.
• Organ of Corti - rests atop the
basilar membrane
• contains approx. 16,000 cochlear
hair cells
Auditory processing.
Perception
of pitch - specific hairs in
specific sections of basilar membrane
identify pitch
Detection of loudness - some hair cells
for a certain frequency require stronger
stimulation; more stimulation = more
hair cells = louder perception
Localization of sound -identified by
timing and intensity
Homeostatic imbalances of hearing.
 Deafness.
• Conduction deafness –possible causes include: ear wax, perforated
eardrum, inflamation, otosclerosis
• Sensineural deafness - nerve damage
 Tinnitus - ringing in the ear
 Meniere's syndrome - attacks of dizziness,
nausea, caused by excess endolymph in the
membranous labyrinth