Special Senses
• General Sense
is touch
• Special Senses are taste, smell, hearing,
and vision
TASTE SENSATION
• Sensory receptors are called
chemoreceptors or taste buds
• Taste buds are located within the filiform
*fungiform or *circumvallate (vallate)
papillae *Contain most of the taste buds
– Filiform – scattered across tongue in V
formations
– Fungiform – scattered across tongue surface;
most abundant at tip and sides
– Vallate – largest and least numerous (7-12);
found as an inverted V at the back of the tongue
TASTE SENSATION
TASTE SENSATION
• Gustatory cells with
gustatory hairs are the
receptor cells
• Basal cells divide and
differentiate into new
gustatory and supporting
cells
– Average life span of a
taste bud 7-10 days
There are four
basic taste
sensations:
sweet, sour,
bitter, salty
and *umami
TASTE SENSATION
Sweet Sour Bitter Salty
sugars acids nicotine metal ions
saccharin caffeine
alcohols quinine
amino acids aspirin
lead salts
• Most taste buds will respond to
a combination of taste qualities
TASTE SENSATION
TASTE SENSATION
• Also found in the mouth:
– Thermoreceptors – for sensing
temperature
– Nociceptors – for sensing pain
– Mechanoreceptors - for
sensing pressure and distortion
OLFACTORY SENSATION
• olfactory epithelium – organ of sense on the roof of the
nasal cavity
• life span is 60 days (neurons)
• cells include: olfactory receptor cells, supporting cells and
basal cells
• mucus continually produced
OLFACTORY SENSATION
The Pathway of Smell
•olfactory cilia of the olfactory receptor cells
captures and dissolves odor molecules
•a mechanism is set into motion to depolarize the
olfactory receptor cell and the message is sent
through the neurons axon and transmitted to
the mitral cells (2nd order neurons) through the
glomeruli (each glomerulus receives only one
type of odor signal)
•mitral cells clean up and amplify the signal to
transmit it to the brain
OLFACTORY SENSATION
OLFACTORY SENSATION
HEARING SENSATION
• External Ear
• Middle Ear – small, air filled cavity
– its borders include the eardrum (tympanic membrane) and a bony wall
• the bony wall has 2 openings: oval or vestibular window & round or cochlear window
– superior border is the epitympanic recess
– auditory (pharnogotympanic or Eustachian) tube links the middle ear with the nasopharynx – functions to equalize air pressure across the tympanic membrane
– houses the ossicles: malleus (hammer), incus (anvil), stapes (stirrup)
• vibration from the eardrum is transmitted by the ossicles to the inner ear through the oval window
• 2 skeletal muscles (tensor tympani & stapedius) control the amount of vibration transmitted
HEARING SENSATION
HEARING SENSATION
Can you hear this?
HEARING SENSATION
• Internal Ear or Labyrinth
– located behind the eye socket in the
temporal bone
– 2 major divisions
• Membranous Labyrinth
– a continuous series of membranous sacs & ducts
contained in the osseous labyrinth
– filled with endolymph
HEARING SENSATION
• Internal Ear or Labyrinth
• Osseous Labyrinth
– a system of canals through the temporal bone
– Filled with perilymph
3 regions
– Cochlea
» houses the spiral organ of Corti, receptor for hearing
– Vestibule
» contains 2 membranous labyrinth sacs (utricle and
saccule) containing equilibrium receptor regions
(maculae)* which responds to gravity and helps to
determine head positioning & linear acceleration
– Semicircular Canals (anterior, posterior, lateral)
» a semicircular duct is contained in each canal and
communicates with the utricle
» the ampulla (enlarged swelling of the duct end)
contains an equilibrium receptor site (crista
ampullaris) that responds to angular movements
HEARING SENSATION
HEARING SENSATION
HEARING SENSATION
STRUCTURE OF VISION
Accessory Structures
* eyebrows – shade & sweat protection
* palpebrae – protection
* conjunctiva – mucous membrane lining the eye
* lacrimal apparatus – secretes tears
* extrinsic eye muscles – movement of the eye
STRUCTURE OF VISION
STRUCTURE OF VISION
The eye wall has three coats or tunics
Fibrous tunic – outermost layer, made of dense
avascular connective tissue with two
regions: sclera and cornea
• Sclera - “white of the eye”
tough, tendon-like
functions: protection, shapes the eye, and
anchors extrinsic eye muscles
• Cornea
transparent (parallel collagen fibers)
covered by stratified squamous epithelium
highly innervated
- covered with epithelium
STRUCTURE OF VISION
Vascular Tunic or Uvea – middle coat of the
eyeball
three regions: choroids, ciliary body, iris
• choroid - brown, highly vascularized membrane
providing nutrients to all eye tunics
• ciliary body - consists of interlacing smooth
muscles called ciliary muscles that control
lens shape; posterior, ciliary processes
secrete aqueous humor to fill anterior cavity;
suspensory ligament (zonule) holds the lens
in place
• iris - colored part of the eye, has a round
central opening called the pupil, has 2 layers
of smooth muscle to vary pupil size
•Eye color and pattern (sticky elastic fibers)
STRUCTURE OF VISION
Sensory Tunic (Retina) - 2 layered innermost tunic
(pigmented layer and neural layer)
•Pigmented layer – external single cell layer
•Neural layer (retina) – internal layer containing 3
neuron types: photoreceptors, bipolar cells,
and ganglion cells
2 types of photoreceptors: rods and cones
rods – dim light, peripheral vision receptors
- more numerous
cones – high light, color vision receptors
- concentrated in the fovea centralis in
the macula lutea
-Optic disc- optic nerve exits the eye creating a
blind spot
STRUCTURE OF VISION
Internal Chambers & Fluids
Anterior Segment –
2 parts: anterior & posterior chamber
Anterior chamber – b/t cornea and iris
Posterior chamber – b/t iris and lens
*filled with aqueous humor circulating from
ciliary processes to the scleral venous sinus
Posterior Segment –
*filled with vitreous humor
functions:
transmit light
support the lens and retina
maintains intraocular pressure aiding
muscle movement
STRUCTURE OF VISION
Lens
avascular, biconvex structure that can flex to
focus light; held by the zonule or suspensory
ligament
STRUCTURE OF VISION
Mechanics of Vision
Light and Optics
• Eyes respond to visible light (400 nm-700 nm)
– Red wavelengths are longest with lowest energy
– Violet wavelengths are shortest with highest energy
• Reflection
– Occurs when light bounces (reflects) off a surface
• Refraction
– Occurs when light is bent as it travels from one
medium to another
– The lens of the eye bends light rays so they
converge on the photoceptors of the retina
Mechanics of Vision
Focusing of light
• Pathway of Light
– Air Cornea Aqueous Humor Lens
Vitreous Humor Neural Layer photoceptors
• Bending of Light
– Bent once through the cornea (most refraction)
– Bent entering and leaving the lens
Mechanics of Vision
Focusing for Distant Vision
• Ciliary muscles are completely relaxed
• Lens is stretched as thin as possible
Mechanics of Vision
Focusing for Close Vision
• Lens Accommodation
– Ciliary muscles contract
– Lens bulges giving shorter focal length
– Near-point of vision – closest point on which we can
focus clearly; maximum lens bulge
• Pupil Constriction
– Limits blurred vision by prohibiting the most divergent
light rays from entering the eye
– Called the Accommodation Pupillary Reflex
• Eyeball Convergence
– Medial rotation of the eyeballs toward the object being
viewed
Mechanics of Vision
• Myopia
– Distant objects are focused in front of
the retina
– Can see close objects but distant
objects are blurred
• Hyperopia
– Distant objects are focused behind the
retina
– Can see distant objects but close
objects are blurred
• Presbyopia
– Loss of accomodation; old person
vision
Mechanics of Vision
• Astigmatism
– Blurred vision is a result of light not focusing as a
point but instead as lines
– Unequal curvatures of the lens
• Nyctalopia
– Night blindness
– Rod function decreases; caused by vitamin A
deficiency
• Stereoscopic Vision
– Smaller total visual field but provides depth
perception
Photoreceptor Cells • Rods
– “regenerate” in morning with first light
– Sensitive, best for night vision and peripheral vision
– Absorb all wavelengths of light by perceived in gray tones
– Information is summated resulting in fuzzier vision
– Deep purple pigment, Rhodopsin
• Cones
– “regenerate” at night with darkness
– Need to be activated by bright light
– Contain pigments that give a colored view of the world
– Each cone has its own neuron to the ganglion and to the
visual centers of the brain
– Pigments are (Photopsin) retinal and opsin (red,green,blue)
Color Blindness
Lack of one or more cone types
3 types of cones
short (S) wavelength cones (blue)
medium (M) wavelength cones (green)
long (L) wavelength cones (red)
Mechanics of Vision
How do you see the world?
Light and Dark Adaptation
• Light Adaptation occurs as we move from dim light to
bright light
– Both rods and cones are stimulated and we see only
white light; large amounts of photopigments breakdown
– To adapt, retinal sensitivity decreases
– The cones take over within 60 seconds and improve
vision in 5-10 minutes
• Dark Adaptation occurs as we move from bright light to
dim light
– Cones stop functioning
– Rod pigments were bleached by the bright light
– Rhodopsin begins to accumulate