A & P Chapter 17 Special Senses

The Special Senses Include:
smell (olfaction), taste (gustation), vision, hearing, and equilibrium (balance)

Sense of smell
Called olfaction, is a chemical sense

Smell is linked to the…
cerebral cortex and limbic system

Olfactory epithelium
has 10-100 million receptors per square inch
located in the superior part of the nasal cavity

chemicals that can stimulate the olfactory apparatus

Olfactory epithelium is made up of:
1) olfactory receptors
2) supporting cells
3) basal (stem) cells

Olfactory receptors
receive stimulation, live about one month
are bipolar (axon and dendrite)
have olfactory hairs projecting from a dendrite into the air path

Supporting (olfactory) cells
columnar epithelial cells
provide support, nourishment, electrical insulation, and detox

Basal (stem) cells
located between supporting cells
produce new olfactory receptors (replaced monthly)

Olfactory (Bowman’s) glands
throughout olfactory epithelium
produce mucous which dissolves odor-ants so that transduction can occur and maintains a moist surface

Facial Nerve (cranial nerve VII)
when stimulated can set off olfactory glands and cause a runny nose or watery eyes

ANY special sense has to transduce

Olfactory Transduction
occurs at or on the olfactory hair

Basic Olfactory Pathway
1)Odorant causes chemical reaction
2)sodium enters cytosol
3)depolarization of olfactory receptor cell membrane occurs
4)nerve impulse is triggered
5)axons carry impulse through the cribiform plate
6)then terminate in the brain and synapse with dendrites of the olfactory bulb
7)olfactory bulb axons form the olfactory tract and go to the primary olfactory area of the cerebral cortex
8) some also go to the limbic system and hypthalamus

Primary Olfactory area of the Cerebral Cortex
where the conscious awareness of smell begins

Frontal Lobe
odor identification area

Olfactory Adaptation
1) Low threshold- we can detect odors down to the 1/25 billionth of a milligram per milliliter of air.
2) Olfactory adaptation is RAPID- 50% after one second/ complete after one minute

reduced ability to smell
affects about half of those over 65 and 75% over 80
caused by neurological changes, drugs, and smoking

Sense of Taste and is a Chemical sense

Five Primary Tastes
sour, sweet, bitter, salty, and umami (meaty/savory)

reported by Japanese scientist
arises from monosodium glutamate (MSG)

Taste Bud Anatomy
10,000 in the oral area
Location: tongue, soft palate, pharynx, and epiglottis

Taste bud Structure
oval body located mainly on the dorsal side of the tongue

Taste bud: Has 3 kinds of epithelial cells
Supporting cells, gustatory receptor cells, and basal cells

Supporting (gustatory) cells
surround and support about 50 gustatory receptor cells per taste bud

Gustatory receptor cells
the working cell of the taste bud
Lifespan: 10 days
have gustatory hairs the extend through the taste pore to contact food particles

Gustatory hairs
One hair for each receptor cells

Basal cells: (gustatory)
produce supporting cells which become receptor cells

Taste bud papillae
elevated areas on the tongue

Papillae with taste buds
vallate, fungiform, and foliate

Papillae without taste buds

Vallate Papillae
Wall-like, form inverted V-shaped row at the back of the tongue, consists of 12 papillae each with 100-300 taste buds

Fungiform Papillae
mushroom-like, contain 5 taste buds each, scatted over entire surface of tongue

Foliate Papillae
leaf-like, located in small trenches on the lateral edge of tongue, most of their taste buds degenerate after childhood

Filiform Papillae
thread-like, lack taste buds, have tactile receptors, increase friction during chewing

Gustatory Adaptation
occurs in 1-5 minutes depending on the taste
Most sensitive- bitterness
Least sensitive- sweet and salty

important to human survival
cerebral cortex processes visual information

The Eye
over half of the sensory receptors in the human body are in the eye

is electromagnetic radiation which is an energy in the form of waves that radiate from the sun

Visible Light
Range: 400-700 nanometers (wavelength)
The eye can only detect visible light

Reflected VS. Absorbed
Our eyes see reflected light from an object not absorbed light

Accessory structures of the Eye
eyelids, eyelashes, eyebrows, lacrimal apparatus, and extrinsic eye muscles

Eyelids (Palpebrae) Functions
shade, protection, and lubrication

Eyelid Structure
Upper and Lower
Composed of: epidermis, dermis, subcut layer, orbicularis oculi muscle, tarsal glands, tarsal plate, palpebral fissure, and conjunctiva

Orbicularis Oculi Muscle
Part of the eyelid (palpebrae)
used for opening and closing (blinking)

Tarsal glands and Plate
Tarsal glands (meibomian)- lubricant between lids; keeps them from sticking together
Tarsal Plate- gives form and support to the eyelids

Palpebral Fissure
gap between the eyelids

thin mucous membrane that lines and protects the inner aspect of the eyelids and passes onto the anterior surface of the eyeball

Eyelashes and Eyebrows Functions
Protection from foreign objects, perspiration, and rays of sunlight

Lacrimal Apparatus Components in Order:
1) lacrimal gland
2) lacrimal duct
3)lacrimal canal– into the superior or inferior lacrimal puncta
4) lacrimal sac
5) nasal cavity

Lacrimal gland
produce and drain lacrimal fluid (tears)

Lacrimal Apparatus Pathway
Lacrimal gland drain through lacrimal ducts, then through the lacrimal canals into the lacrimal puncta and then into the lacrimal sac of the nasal cavity

Lacrimal fluid consists of:
water, salts, mucus, and lysozyme(protective bacteriocidal enzyme)

Extrinsic Eye Muscles other name
also called “extraocular muscles ” meaning=(outside the eyeball)

Extrinsic eye muscles
Extend from the bony orbit of the eye onto the exterior surface of the eyeball at the sclera
Six move each eye
4 rectus, 2 oblique
innervated by cranial nerves III, IV, or VI

Extrinsic Eye Muscle Types
4 rectus: superior, inferior, lateral, and medial
2 oblique: inferior and superior

Adult eyeball diameter
1 inch (2.5 cm)
1/6 exposed, 5/6 protected by orbit

Eyeball wall’s 3 layers
Called Tunics
1) fibrous tunic
2) vascular tunic
3) nervous tunic (retina)

Fibrous Tunic:
superfical (outer) layer
consists of: the cornea and the sclera

Part of the fibrous tunic
the transparent coat over the iris which HELPS focus light onto the retina
Composed of: non-keratinized stratified sq. epithelium, collagen fibers, fibroblasts, and simple sq. epithelium

Sclera= hard
the hard layer of dense connective tissue covering the eye
the “white” of the eye
covers entire eye (except the cornea)
gives rigidity, shape, support and attachment points for extrinsic muscles to the eye
posteriorly pierced by the optic nerve (cranial nerve II)

Sclera Vinous Sinus
Also called the canal of Schlemm
opening at the junction of the cornea and sclera
aqeuous humor drains into from the eye to the bloodstream

Vascular Tunic
middle layer
Composed of: choroid, ciliary body, iris, and pupil

highly vascular posterior part of vascular tunic
lines internal surface of sclera
it’s blood vessels nourish the posterior retina
contains melanocytes which produce melanin
**the melanin absorbs light rays and prevents the scattering of light throughout the eyeball**

Ciliary body
anterior part of vascular tunic, contains melanin
Contains: ciliary processes and ciliary muscles

Ciliary processes
folds on the internal surface of the ciliary body which secrete aqueous humor

Ciliary muscles
circular band of smooth muscle which contracts or relaxes to adjust tightness of suspensory ligaments which are attached to the lens

Suspensory ligaments
attached to the lens
focus the lens for you

the refractive medium of the eye
transparent and avascular
Function: focus light rays onto the retina
made of layers of proteins called crystallins

lens loses elasticity and thus it’s ability to focus

Iris= means rainbow
colored portion of the eye
Main function: regulate the amount of light entering the eye through the pupil
lays between the cornea and the lens
contains circular and radial muscle fibers attached to the ciliary processes for constriction and dilation
contains melanin- gives eyecolor

hole in the center of the eye
appears black because you’re actually seeing the choroid and retina in the back of the eye

Pupil diameter
regulated by the response of autonomic reflexes
determined by constrictor pupillae and dilator pupillae

Constrictor Pupillae
circular muscle fibers
contract in bright light to SHRINK the pupil
innervated by the parasympathetic fibers

Dilator Pupillae
radial muscle fibers
contract in dim light to dilate the pupil (enlarge)
innervated by the sympathetic fibers

Nervous Tunic (Retina)
the starting point of the visual pathway

the inner layer of the posterior 2/3 of the eyeball

Pigmented epithelium
part of the retina, no vision, absorbs stray light to help keep the image clear

Retinal layers include
Neural layer— 1) photoreceptor layer 2) bipolar cell layer 3) the ganglion cell layer

Neural layer
a multilayered outgrowth of the brain

Photoreceptor layer
with rods and cones: transduces light into action potentials which travel through the outer synaptic layer to the bipolar cell layer

Bipolar cell layer
contains horizontal and amacrine cells which modify nerve impulses
receives impulses from the photoreceptor layer and sends them through the INNER synaptic layer to the ganglion cell layer

Ganglion cell layer
it’s axons form the optic nerve leaving the eyeball at the optic disc(blind spot)–
impulses travel from here to the thalamus and primary visual cortex

Optic disc
the blind spot, where there is no vision since no images can be formed there(no rods or cones)

Central retinal artery and vein
nourish and drain blood from the retina
exit through the optic disc

Macula lutea
the exact center of the posterior portion of the retina corresponding to the visual axis of the eye–
fovea is located in the middle

fovea centralis
is a small depression in the center of the macula latea
*sharpest vision occurs here*
Contains ONLY *cones* for color vision
area of highest visual acuity or resolution

Rods & Cones
specialized cells that begin the process by which light is converted to a nerve impulse and sent to the brain

rod-shaped/ over 120 million per retina
allow us to see in dim light & discriminate between dark and light
permit us to see shapes and movement (motions)
absent from fovea and macula lutea
dense at periphery of retina

6 million per retina
allow us to see color in brighter light
for color vision and sharpness (acuity)
concentrated in the fovea

used to examine the retina

Detached retina
caused by head trauma
fluid accumulates between layers of the retina
causes distorted vision or blindness

Age-Related Macular Disease
macular degeneration
degeneration of the retina and macula lutea in older people
Effects: keep peripheral vision but lose ability to look straight ahead

Lens divides the interior of the eye into
1) the anterior cavity &
2) the vitreous chamber

Anterior cavity
the space anterior to the lens
has two chambers: anterior and posterior

Anterior Cavity/ Anterior Chamber
the space between the cornea and the iris

Anterior Cavity/ Posterior Chamber
between the iris and the lens

Aqueous humor
fills both the anterior and posterior chambers of the anterior cavity
nourishes the lens and cornea
produced by the ciliary body
replaced every 90 minutes

Flow of aqueous humor
flows from posterior chamber into the anterior chamber through the pupil

Vitreous chamber
large space between the lens and the retina
contains the vitreous body

Vitreous body
transparent jelly-like substance
holds the retina flushed up against the choroid giving an even surface for receiving clear images
is never replaced

Intraocular Pressure
pressure in the eye produced by aqueous humor
Normally 16 mm Hg
it and the vitreous body maintain the shape of the eye and keep the retina attached to the choroid

excessive intraocular pressure
caused by a problem with the drainage of aqueous humor
can cause retina degeneration or blindness

the bending of light rays as they pass from one substance (air) into another substance (cornea) with a different density

Light is refracted by
the anterior and posterior surfaces of the cornea and the lens
75% refracted by the cornea
25% refracted by the lens

increase in curvature of the lens for near vision
function of the ciliary muscles pulling on the suspensory ligaments

decreased tension on suspensory ligaments
lens becomes spherical (convex)
focus on NEAR objects

increased tension on suspensory ligaments
lens flattens
allows focus on FAR objects

Near point of vision
the minimum closest distance from the eye that an object can be clearly focused

Emmetropic Eye
normal eye, normal vision
can refract light from an object 20 ft away so a clear image forms on the retina

eyeball is too LONG front to back
concave glasses required

or (hypermetropia) farsightedness
eyeball is too SHORT
convex glasses required

irregular curvature of the cornea or lens causing blurred vision

Circular muscles
contract to constrict pupil

Radial muscles
contract to dilate pupil

Binocular Vision
both eyes look at the same object at the same time

the medial movement of both eyes so that both are directed toward the object being viewed
necessary so that light from the object strikes both retinas at the same points
extrinsic muscles coordinate convergence

Outer Segment of Rods and Cones
contain photopigments
is where receptor potentials arise
Rods= rhodopsin
Cones= 3 different opsins- three primary colors

colored proteins that change structurally when they absorb light

2 Parts of Photopigments
Opsin ( a glycoprotein) & Retinal ( derivative of Vitamin A)

the light absorbing part of ALL visual photopigments

the base of the photopigment
There are 4 different opsins.
Rhodopsin- is in the rod
3 other opsins are in the cones

Inner Segment of Rods and Cones
contains the cell nucleus, golgi complex, and mitochondria
synaptic terminals are located at the proximal ends

Vision Transduction
“the alternating bleaching and regeneration of photopigments”
Photopigments respond to light in a 3 step cyclical process
1) Isomerization
2) Bleaching
3) Regeneration

Step 1: Isomerization
Light causes ‘cis-retinal’ to straighten into ‘trans-retinal’
“cis”=means at an angle
“trans”=means straight across
“retinal”= light absorbing portion
The “cis-retinal” absorbs a photon of light and then straightens out and becomes “trans-retinal” which leads to a receptor potential

Step 2: Bleaching
After a minute, “trans-retinal” separates from the opsin base and becomes colorless.
Remember: opsin contains the colors

Step 3: Regeneration
“Retinal Isomerase” converts ‘trans-retinal’ back to ‘cis-retinal’
Regeneration is complete when: ‘cis-retinal’ binds to another opsin and reforms a new functional photopigment.
Vitamin A in the pigment epithelium helps assist in this step

Regeneration Speed: Cones and Rods
Cone-photopigments regenerate faster than rods, take only 90 secs
Rod- Rhodopsin photopigments regenerate by 1/2 in about 5 minutes, but can take up to 30-40 minutes to fully regenerate

Bleaching and Regeneration of Photopigments
accounts for a lot of sensitivity change but not all of it.
adaptation occurs because of this

Light Adaptation
Moving from Dark to Light
Example: Constriction of pupils
Adapts faster than dark adaptation

Dark Adaptation
Moving from Light to Dark
Example: Pupil dilation

Full Darkness Effects
light sensitivity increases because photopigments regenerate
Cones regenerate in full darkness in 8 minutes so barely visible light is seen as color
After time (+5 mins) rods regenerate so barely visible light will be seen as a gray-white color

Color Blindness
1) the inability to distinguish between certain colors
2) is inherited
3) an absence of certain cone photopigments
4) more common in males
5) Most common type: red-green color blindness, meaning red or green cones are missing

Night Blindness
also called “Nyctalopia”
1) a deficiency in rhodopsin
2) person has the inability to make the normal amount of rhodopsin
3) Possibly due to a Vitamin A deficiency

Visual Info in the Optic Nerve travels to:
1) the Hypothalamus- establishes sleep patterns
2) the Midbrain- controls pupil size & coordination of head and eye movements
3) Occipital Lobe- for vision

Visual Field
everything that can be seen by one eye is that eye’s visual field
Binocular Vision Field- left and right visual fields overlap due to our eyes being anterior

Two Regions of the Visual Field
1) Nasal- central half, toward the nose or midline/ axons of ganglion cells extend to the thalamus on the OPPOSITE side/ nasal fibers cross at the optic chiasm
2) Temporal- peripheral half, sides of the body (right and left)/ axons of ganglion cells extend to the thalamus on the SAME side

Example of Visual Field
Left Occipital Lobe- receives input from the right nasal 1/2(right eye) and the left temporal half(left eye)
Complete picture of the RIGHT side is made

The Ears Function
a receptor for sound waves
*transduces sound vibrations* with amplitudes as small as the diameter of an atom of gold (0.3nm) into electrical signals
*1000 times faster than photoreceptors in the eye*

The External(outer) Ear
collects sound waves and channels them inward
Consists of:
1) Auricle(pinna)- flap of skin over cartilage, collects sound waves
2) Helix- the rim of the auricle
3) Lobule- the ear lobe
4) External auditory canal(meatus)- curved tube, leads to eardrum &
contains:—>>Ceruminous glands that secrete cerumen(earwax)
5) Tympanic membrane- eardrum

Tympanic Membrane
vibrates back and forth when sound saves strike it
between the auditory canal and middle ear
Composed of: collagen, elastic fibers, fibroblasts(connective tissue) covered by simple CUBOIDAL epithelium
Perforated eardrum- tearing or a hole in the eardrum

Middle Ear= tympanic cavity
small, air-filled cavity in the temporal bone lined by epithelium.
Function: convey vibrations to the oval window
Contains: the auditory ossicles, oval window, round window, eustacian tubes, and muscles

Auditory Ossicles= smallest bones of the body
are connected by synovial joints and include:
1) Malleus(hammer) attaches to the internal surface of the eardrum and it’s head articulates with the incus
2) Incus(anvil)- the middle bone, articulates with head of the stapes
3) Stapes(stirrup)- footplate of the stapes attaches to the oval window.

Round Window
is for pressure equalization
is covered by a second tempanic membrane and lays just below the oval window

Auditory(pharyngotympanic) tube- Eustacian tubes
connects the middle ear with the nasopharynx(top of throat)
allows pressure equalization on both sides of the eardrum
an opening for pathogens to escape

Tensor tympani muscle
attached to malleus to limit movement & stiffens eardrum to prevent damage from loud noises
supplied by the trigeminal nerve(V)

Stapedius muscle
inserts onto the stapes
SMALLEST muscle in the body!!
Protects oval window by dampening large vibrations
supplied by the facial (VII) nerve

Internal (Inner) Ear
also called the labyrinth because of it’s complicated series of canals
houses the receptors for hearing and equilibrium

Internal Ear Components
1) bony labyrinth
2) membranous labyrinth
3) cochlea

Bony Labyrinth
series of cavities in the petrous portion of the temporal bone
Lined with periosteum and filled with perilymph
houses the semicircular canals, vestibule, and the cochlea

cushioning fluid in the bony labyrinth
chemically similar to cerebrospinal fluid and surrounds and protects the membranous labyrinth

Cavities of the Bony Labyrinth Include:
1) Vestibule- oval-shaped central portion
2) 3 semicircular canals: Anterior, posterior, and lateral. They lay superior and posterior to the vestibule and are arranged at right angles in an X-Y-Z, 3-D view.
Anterior and Posterior semi canals are vertical
Lateral semi canal is horizontal

Membranous Labyrinth
a series of epithelial sacs and tubes housed in the bony labyrinth
forms the organs hearing and equilibrium
filled with ENDOLYMPH

Parts of the Membranous Labyrinth
1) utricle “little bag” and the saccule “little sac”- they are within the vestibule and are connected by a duct
2) 3 semicircular ducts(membranous semicircular canals) are
within the semicircular canals, are all connected at the utricle, & are all swollen at one end
3) Ampulla- swollen ends of the semicircular ducts

“snail-shaped” a bony, spiral canal that makes almost three turns around a central bony core called the “modiolus”

Cochlea- Structures of the spiral canal
1) Scala vestibuli
2) Scala tympani
3) Cochlear duct

Scala vestibuli
contains perilymph, ends at the oval window and is part of the bony labyrinth

Scala tympani
contains perilymph, ends at the round window and is also part of the bony labyrinth

Cochlear duct
“scala media” a continuation of the membranous labyrinth into the cochlea.
contains Endolymph
separates the scala vestibuli and the scala tympani except at the apex(top) of the cochlea where they are joined at the “helicotrema”

joins the scala vestibuli and scala tympani at the apex of the cochlea

Vestibular membrane
separates the cochlear duct from the scala vestibuli

Basilar membrane
separates the cochlear duct from the scala tympani

Organ of Corti “Spiral Organ”
the organ of hearing consisting of supporting cells and hair cells that rest on a basilar membrane & extend into the endolymph of the cochlear duct

Within the Organ of Corti
16,000 hair cells: the receptors for hearing, each with 30-100 stereocilia(microvilli)
At the basal end- hair cells synapse with 1st order sensory neurons whose cell body is in the spiral ganglion

Cranial Nerves to the Ear
1)Vestibularochlear nerve- branches into the vestibular and cochlear branches to serve all structures of the cochlea and vestibule.

Vestibular Branch Divides Into:
1) Ampullary nerves- serve ampulla of each duct
2) Utricular nerve- serves utricle
3) Saccular nerve- serves saccule

Cochlear Branch
has a “spiral ganglion” in the bony modiolus

Sound Waves
“have to have a MEDIUM”
alternating high and low pressure regions traveling in the same direction through a medium (such as air)
originates for a vibrating onject

the frequency of a vibration
1) higher frequency- higher pitch
2) lower frequency- lower pitch

Best Hearing Range
500 – 5,000 hertz(cycles per second)

Audible Range
20 – 20,000 hz

Speech Range
100 – 3,000hz

the volume of sound
it is the size or amplitude of the vibrating wave.
greater the intensity the greater volume “loud”

Decibels (db)
units in which sound is measured
Normal conversation= 60db
Pain level= above 140db
Hearing protected required by OSHA= 90db

means balance
1) static equilibrium
2) dynamic equilibrium

Static Equilibrium
refers to the maintenance of the position of the body relative to the force of gravity
Example: tiliting the head or acceleration or deceleration
a function of the otolithic organs

Dynamic Equilibrium
the maintenance of body position relative to rotational acceleration or deceleration
is a function of the semicircular ducts

Vestibular Apparatus
collective name given to the receptor organs for equilibrium

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