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