Senses
Five Senses Smell Taste Balance or equilibrium Vision Hearing
Smell Olfaction: provided by
paired olfactory organs, located in roof of nasal cavity on either side of the nasal septum
A German Shepherd has olfactory receptor surface 2 times greater than ours
When olfactory receptors are stimulated, nerve impulses are relayed to the CNS through the olfactory nerve
Taste Taste receptors are found on superior
surface of the tongue, clustered together to form taste buds
Four primary taste sensations: sweet, salt, sour, bitter
Taste Buds
Balance and Equilibrium Receptors for balance and equilibrium
are housed in the ear
The Eye Located in the orbits Orbits are formed by 7
skull bones Sphere measuring
about one inch in diameter
About 1/6 of anterior surface can be seen
Other 5/6 of the eye is enclosed and protected by a cushion of fat and orbit
External Accessory Structures 6 external eye
muscles They attach to
outer surface of eye
They allow for movement of eyeball
They are controlled by cranial nerves
Eyelids Close firmly to protect
the delicate surface of the eye
Continual blinking movements keep anterior surface lubricated and free from dust and debris
Contain sweat and sebaceous glands, if infected=sty
Hairs of eyelashes prevent foreign particles and insects from reaching surface of eye
Eyebrows divert sweat
Conjunctiva
Protects eyeball Lines interior surface of
eyelids Covers outer surface of
eyeball Transparent mucus
membrane Contains many nerve
endings, very sensitive *Considered to be
accessory*
Lacrimal Apparatus Tear glands Located above and to outer part of
each eye Produces tears that flow over eye
when blinked, moistened and lubricate eye
Sclera: outer layer *White outer covering “white of
the eye” Tough and Fibrous connective tissue Provides protection and serves as an
attachment site for the eye muscles Portion of sclera is cornea
Choroid: middle layerBetween the retina and scleraComposed of layers of blood
vessels(vascular coating) that nourish the back of the eye
Supplies blood , oxygen, and nutrients to the eyeball
Retina: inner layer of the eye Contains millions
of receptor cells Rods and Cones
Rods and cones are called receptor cells because they respond to light
Rods The receptors
for night vision or dim light
Interfering with rod function leads to night blindness
Night blindness usually a deficiency in vitamin A
Cones *Receptors for
daylight and color Three variations of
cones, each type is most sensitive to one of the primary colors, red, green, blue
Lack of all 3 cone types results in total color blindness which is very rare almost exclusively in males Color Blindness Test
Optic Nerve *Visual impulses are
sent to the brain Rods and cones are
distributed over entire retina except where optic nerve leaves the eyeball the “blind spot”
We aren’t aware of the blind spot because our eye are always moving
Cornea Transparent anterior portion First structure of eye through
which light passes Well supplied with nerve
endings, mostly pain fibers When touched, blinking and
increased tearing occur Most exposed part of the
eye, vulnerable to damage Has no blood vessels, tissue
can be transmitted from one person to another without worry of rejection
Ciliary Body/Muscle *Controls shape of lens Important in the focusing process Supports lens through suspensory ligaments Secrete aqueous humor
Lens *Function is to focus the image on the
sensory receptors in the retina Near or far away
Focusing depends on refraction, or bending of light from the object
Divides eye into two chambers: aqueous chamber and vitreous
Aqueous Chamber *Anterior cavity between the lens and
the cornea Filled with aqueous humor, a clear watery
fluid Provides nutrients for the lens and
cornea *Maintains intraocular pressure and
shape of the eye If pressure is blocked and pressure
increases leads to glaucoma
Vitreous Chamber Posterior cavity Occupies entire
orbit behind lens Filled with vitreous
humor Helps prevent the
eyeball from collapsing inward
Helps maintain pressure and shape
Iris Gives us our eye color. Front portion of choroid Formed from circular and
radial smooth, involuntary muscles
*Regulates amount of light entering the eye so we can see as clearly as possible
In close vision and bright light, circular muscles contract, pupil constricts
In distant vision and dim light, radial fibers contract to enlarge or dilate pupil, letting in more light
Pupil Rounded opening of the iris Looks black because inner
eye is dark Size determines how much
light will enter the eye
*Flashlight Test*
What Do Glasses and Contact Lenses Really Do? Eye Conditions 47% of people in U.S. wear
contacts or glasses In normal eye, the ciliary muscles
are relaxed and lens is flattened, the distant image is focused on retina
Irregularities in shape of lens or cornea can affect the clarity of the visual image (astigmatism), corrected with glasses.
Myopia (nearsightedness): the eyeball is too deep, image of distant object will form in front of retina and be blurry. Vision at close range will be normal because the lens will be able to round up as needed
Eye Conditions Cont. Hyperopia (farsightedness):
If eyeball is too shallow this will occur. The ciliary muscles must contract to focus even a distant object on the retina, and at close range the lens cannot provide enough refraction
Presbyopia (old man’s eye): Older individuals become farsighted as their lenses become elastic.
Vision Test *Vision tests are commonly
done using a Snellen Chart.* *20/20 vision:* rating the
clarity of vision. A person is seeing details at a distance of 20 feet as clearly as a “normal” individual would.
20/15: Is better than average for at 20 feet the person is able to see details that would be clear to a normal eye only at a distance of 15 feet
Legally blind: 20/200
Ophthalmoscope Instrument use to
examine the interior of the eye
The Ear
Two Sensory Functions of the EarEquilibrium: informs us of
the position of the body in space by monitoring gravity, acceleration, and rotation
Hearing: enables us to detect and interpret sound waves
Senses of equilibrium and hearing are provided by inner ear
3 Parts of the Ear
Basic receptors for these senses are ciliated cells called hair cells. Movement of the cilia cause the hair cells to produce nerve impulses which are sent to the brain via the eighth cranial nerve.
External Ear*Pinna/auricle:* external cartilaginous
flap that catches sound waves. Surrounds the entrance to external auditory canal.
External Ear Auditory canal: short,
narrow chamber lined with fine hairs and sweat glands. Hair helps prevent the
entry of foreign objects and insects.
Ceruminous glands (sweat glands) secrete cerumen (ear wax) which slows growth of microorganisms.
Middle Ear Sound waves are
collected and conducted through the air on their way to the tympanic membrane (eardrum)
*Tympanic membrane:* is a thin sheet that separates the external ear from the middle ear
Process of hearing begins when sound waves enter the auditory canal
Middle Ear *Separated from the
external auditory canal by the tympanic membrane*
Connects middle ear with nasopharynx called the auditory tube or Eustachian tube. This tube serves to
equalize the pressure on either side of the eardrum but also provides a path for microorganisms to enter and cause middle ear infections
Middle Ear-Ossicles *Three tiny ear bones* These bones connect the tympanic membrane with
the receptors of the inner ear and amplify the sound about 20 times
Malleus (hammer): is attached to the inside surface of the tympanum.
Incus (anvil): attaches malleus to the inner stapes. Stapes (stirrup): is attached to the oval window, a
membrane in the inner ear Vibration of the ear drum causes the three ear
bones to move, and rocks the stapes against the oval window
Inner Ear
Inner ear structures and functions Senses of equilibrium and hearing are
provided by the receptors within the inner ear Receptors for both of these lie in a network of
fluid-filled tubes and chambers known as membranous labyrinth which contains a fluid called endolymph
Bony labyrinth: surrounds and protects membranous labyrinth
Perilymph: fluid that flows between the bony and membranous labyrinth
Sound is conducted through the fluid
Three Sub-Divisions Of The Inner Ear *Semicircular canals: balance* Vestibule: balance Cochlea: hearing
Semicircular Canals
Provide information concerning rotational
movement of the headEach canal encloses a slender semicircular
duct that contains endolymph and a sensory receptor
Each semicircular duct responds to one of three possible movements: horizontal rotation: shaking the head “no”, front to back: nodding “yes”, side to side: tilting the head
Continuous movement of the fluid can lead to motion sickness
Vestibule Between the semicircular canals and
cochlea Provide the sensation of gravity and
acceleration Provide information on which way is up
or down, helps keep our heads erect
Cochlea Function in hearing Looks like a snail *Contains Organ of Corti: extend
along the entire length of the coiled cochlear duct, changes vibrations to nerve impulses
*FYI: Buzzing or Ringing in the ears is called “Tinnitus.”*
Let’s put it all together!How Your Ears Work