1. The Senses

2. The Senses General senses of touch Temperature Pressure Pain
Special senses
Smell / Taste
Sight
Hearing / Equilibrium (balance)

3. The Special Senses Sight – The eye and Vision
Smell / Taste – Chemical senses – Nose and Tongue
Hearing / Equilibrium (balance) – The Ear

4. The Eye and Vision

5. The Eye Visual organ – the eye
70% of all sensory receptors are in the eyes.
40% of the cerebral cortex is involved in processing visual information.
Each eye has over a million nerve fibers.
Protection for the eye
Most of the eye is enclosed in a bony orbit, in other words your eye socket.
A cushion of fat surrounds most of the eye.

6. Accessory Structures of the Eye
Eyelids
Designed to protect the eye, and keep moisture distributed over the surface of the eyeball.
Slide 8.3a

7. Accessory Structures of the Eye
Eyelashes
Acts as a dust and particle protector for the eye.
Has modified sebacious glands produce an oily secretion to lubricate the eye.
Ciliary glands
modified sweat glands between the eyelashes.

8. Tear ducts or the Lacrimal apparatus
Tears contain mucous, antibodies, (anti-bacterial)
keeps the surface of the eye moist.
Lacrimal gland – produces the tears.
Lacrimal sac – fluid empties into nasal cavity.

9. Eye Muscles Muscles attach to the outer surface of the eye.
Produce eye movements.

10. Structure of the Eye The wall of the eye is composed of three tunics
Sclera & Cornea fibrous outside layer
2. Choroid – middle layer
3. Sensory tunic – (retina) inside layer.

11. 1. The Fibrous Tunic Sclera Cornea
Tough white connective tissue layer.
The “white of the eye”
Cornea
Transparent, central anterior portion.
Allows for light to pass through.
Repairs itself easily.
The only human tissue that can be transplanted without fear of rejection.

12. Choroid Layer Blood-rich nutritive tunic
Pigment prevents light from scattering.
Modified interiorly into two structures.
Cilliary body – smooth muscle
Iris
Pigmented layer that gives eye color
Pupil – rounded opening in the iris

13. Sensory Tunic (Retina)
Contains receptor cells (photoreceptors)
Rods
Cones
Signals pass from photoreceptors and leave the retina toward the brain through the optic nerve

14. Neurons of the Retina and Vision
Cones – 3 types detect different colors
Densest in the center of the retina.
Fovea centralis – area of the retina with only cones.
Lack of one type = color blindness.

15. Neurons of the Retina and Vision
Rods
Most are found towards the edges of the retina
Allow dim light vision and peripheral vision
Perception is all in gray tones

16. The Iris Visible colored part of the eye Composed of smooth muscle
Pupil – the round, central opening that is a set of special muscles which acts to vary the amount of light entering the eye.

18. Pupil dilation and constriction

19. Lens
Biconvex crystal-like structure
Held in place by ligaments.

20. Lens – what it does
Light must be focused to a point on the retina for optimal vision
The eye is set for distance vision (over 20 ft away)
The lens must change shape to focus for closer objects
Slide 8.16

21. Internal Eye Chamber Fluids
Vitreous humor
Keeps the eye from collapsing
Gel-like substance behind the lens
Lasts a lifetime and is not replaced
Aqueous humor
Similar to blood plasma
Watery fluid found in chamber between the lens and cornea
Provides nutrients for the lens and cornea

22. Vision
Each eye captures its own view and the two separate images are sent on to the brain for processing.
When the two images arrive simultaneously in the back of the brain, they are united into one picture.
The mind combines the two images by matching up the similarities and adding in the small differences.
The combined image is more than the sum of its parts. It is a three-dimensional stereo picture.

23. BLIND SPOT BLIND SPOT – little test
The area on the retina where the optic nerve enters the eyeball.
This area has no photoreceptors and therefore no visual input.
The cortex appears to fill-in this missing information so we are not conscious of the blind spot.
No photoreceptor cells are at the optic disk, or blind spot.
BLIND SPOT – little test
Slide 8.16

24. The Eye - basic parts review

25. Correcting the Eye Nearsightedness = myopia Farsightedness = hyperopia
Focus of light in front of retina
Eyeball too long or lens too strong
Distant objects are blurry
Farsightedness = hyperopia
Focus of light beyond the retina
Short eyeball or lazy lens
Near objects are blurry.
Difficulty seeing clase objects = presbyopia
Inability of the lens to focus properly at close objects
Caused by the aging of the eye.
Special reading glasses needed.

30. Cataracts
The natural lens looses its transparency due to damage to its fibers over time.
Lens fibers are not replaced.
When the lens of the eye turns cloudy enough to impair vision, it is considered a cataract.
They are the main cause of blindness worldwide.
Most individuals over 60 years old develop some degree of cataract.
Treatment consists of a safe and precise surgical procedure.

31. The Ear – Hearing and Equilibrium

32. The Ear Houses two senses
Hearing
Equilibrium (balance)
Receptors are mechanoreceptors, they react to sound waves.

33. Anatomy of the Ear The ear is divided into three areas
Outer (external) ear
Middle ear
Inner ear

34. Involved in hearing only
The External Ear
Involved in hearing only
Structures of the external ear
Pinna (auricle)
External auditory canal

35. The External Auditory Canal
Narrow chamber in the temporal bone
Lined with skin
Ceruminous (wax) glands are present
Ends at the tympanic membrane or ear drum.

36. The Middle Ear or Tympanic Cavity
Air-filled cavity within the temporal bone
Only involved in the sense of hearing

37. The Middle Ear or Tympanic Cavity
Two tubes are associated with the inner ear
The opening from the auditory canal is covered by the tympanic membrane (Ear drum)
The auditory tube connecting the middle ear with the throat
Allows for equalizing pressure during yawning or swallowing
This tube is otherwise collapsed

38. Bones of the Tympanic Cavity
Three bones span the cavity (the smallest bones in our bodies!!)
Malleus (hammer)
Incus (anvil)
Stapes (stirrip)

39. Vibrations from eardrum move the malleus
These bones transfer sound to the inner ear.
Slide 8.25b

40. Inner Ear or Bony Labyrinth
Includes sense organs for hearing and balance!
Filled with a fluid called perilymph
Slide 8.26a

41. Inner Ear or Bony Labyrinth
A maze of bony chambers within the temporal bone
Cochlea
Vestibule
Semicircular canals

42. Hearing Located within the cochlea
Receptors = hair cells a membrane on it’s inner surface.
Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe of the brain.

43. Equilibrium – Balance/Orientation
Receptor cells are in two structures:
Vestibule
Semicircular canals

44. Equilibrium Static equilibrium
Equilibrium has two functional parts
Static equilibrium
– sense of gravity at rest. Ability to stay still in one place.
Dynamic equilibrium
– angular and rotary head movements. Keeping a sense of where you are at all times
Think of a snowboarder doing a flip and being able to land on their feet.
Figure 8.16a, b

45. Equilibrium
This balance is achieved by vestibular nerve endings in side the Vestibule and the Semicircular canals, sensing the subtle changes in the fluid (endolymph) inside these structures.
Figure 8.16a, b

46. Smell / Taste The Chemical Senses

47. Chemical Senses – Taste and Smell
Both senses use chemoreceptors
Stimulated by chemicals in solution.
Taste has four types of receptors.
Smell can differentiate a very large range of chemicals.
**Both senses complement each other and respond to many of the same stimuli**

48. Olfaction – The Sense of Smell
Olfactory receptors are in the roof of the nasal cavity.
Neurons with long cilia
Chemicals must be dissolved in mucus for detection
Impulses are transmitted via the olfactory nerve
Interpretation of smells is made in the cortex of the Brain

49. The Sense of Smell

50. Taste Taste buds house the receptor organs Location of taste buds
Most are on the tongue
Slide 8.37

51. The Tongue and Taste
The tongue is covered with projections called papillae
Filiform papillae – sharp with no taste buds
Fungifiorm papillae – rounded with taste buds
Circumvallate papillae – large papillae with taste buds
Taste buds are found on the sides of papillae

52. Anatomy of Taste Buds
Figure 8.18
Slide 8.40

53. Taste Sensations Sweet receptors Sugars Saccharine Some amino acids
Sour receptors
Acids
Bitter receptors
Alkaloids
Salty receptors
Metal ions
Slide 8.41

54. SMELL and TASTE
To distinguish most flavours, the brain needs information about both smell and taste.
These sensations are communicated to the brain from the nose and mouth.
Several areas of the brain integrate the information, enabling people to recognize and appreciate flavours. .

55. SMELL and TASTE
So … our senses of Smell and Taste are Complementary, they are partners in interpreting chemical stimuli.
When you have a cold and your nose is blocked, then you will notice that your ability to taste is greatly reduced.

56. Development of the Special Senses
Formed early in embryonic development
Eyes are outgrowths of the brain.
All special senses are functional at birth