1. Senses

2. Five Senses
Smell
Taste
Balance or equilibrium
Vision
Hearing

3. 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

4. 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

5. Balance and Equilibrium
Receptors for balance and equilibrium are housed in the ear

6. 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

7. 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

8. 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

9. 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*

10. 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

11. 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

12. Choroid: middle layer Between the retina and sclera
Composed of layers of blood vessels(vascular coating) that nourish the back of the eye
Supplies blood , oxygen, and nutrients to the eyeball

13. 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

14. 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

15. 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

16. 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

17. 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

18. Ciliary Body/Muscle *Controls shape of lens
Important in the focusing process
Supports lens through suspensory ligaments
Secrete aqueous humor

19. 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

20. 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

21. 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

22. 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

23. Pupil Rounded opening of the iris
Looks black because inner eye is dark
Size determines how much light will enter the eye
*Flashlight Test*

24. 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

25. 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.

26. 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

27. Ophthalmoscope
Instrument use to examine the interior of the eye

28. The Ear

29. Two Sensory Functions of the Ear
Equilibrium: 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

30. 3 Parts of the Ear

31. Basic receptors for these senses are ciliated cells called hair cells
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.

32. External Ear
*Pinna/auricle:* external cartilaginous flap that catches sound waves. Surrounds the entrance to external auditory canal.

33. 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.

34. 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

35. 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

36. 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

37. Inner Ear

38. 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

39. Three Sub-Divisions Of The Inner Ear
*Semicircular canals: balance*
Vestibule: balance
Cochlea: hearing

40. Semicircular Canals

41. Provide information concerning rotational movement of the head
Each 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

42. 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

43. 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.”*

44. Let’s put it all together!
How Your Ears Work