1. The Senses

2. Learning Objectives
Classify sense organs as special or general and explain the basic differences between the two groups
Discuss how a stimulus is converted into a sensation
Discuss the general sense organs and their functions

3. Learning Objectives (cont’d.)
Describe the structure of the eye and the functions of its components
Discuss the anatomy of the ear and its sensory function in hearing and equilibrium
Discuss the chemical receptors and their functions

4. SENSES
Sensory Receptors - detect environmental changes and trigger nerve impulses
- somatic senses (touch, pressure, temp, pain) - special senses (smell, taste, vision, equilibrium)
Where do general sense organs reside – skin, muscles, tendons and joints
Special – smell, taste, vision hearing and equilibrium

5. CLASSSIFICATION Encapsulated – Unencapsulated - free or naked
Free nerve endings (pain, crude touch, temperature, itch, tickle
Unencapsulated - free or naked
Dermis, and deeper

6. Receptors 1. Chemoreceptors = _____________________
2. Pain receptors = ____________________  
3. Thermoreceptors = _____________________
4. Mechanoreceptors = _____________________
5. Photoreceptors =
_____________________
6. Proprioceptors –
INSTANTANEOUS
Chemoreceptor – receptors that respond taste and smell to chemicals –
pain receptors – pain INJURY
Thrmoreceptors - hot and cold
Mechanorecptors – mechanical in nature – equilibrium and balance in the ear
Photoreceptors – nerve receptors stimulated by light – rods and cones of the retina – LIGHT
Proprioceptors – position of body parts and changes (between muscles and tendons)

7. Sensations
Sensation = feeling that occurs when a brain interprets a sensory impulse
Projection = process where the cerebral cortex causes a feeling to stem from a source (eyes, ears)
Sensory adaptation = sensory receptors stop sending signals when they are repeatedly stimulated
What do you think is going on in this picture?
Sensory Deprivation is a technique initially used by neuro-psychiatrists designed to deliberately reduce or completely remove stimuli from one or all of the senses.

8. CONVERTING A STIMULUS INTO A SENSATION
All sense organs are able to detect a particular stimulus
A stimulus is converted into a nerve impulse
A nerve is perceived as a sensation in the CNS
Must have a stimulus, nerve impulse and a intact CNS

9. Somatic Senses
1. Sensory Nerve Fibers - epithelial tissue, pain and pressure 2. Meissner's corpuscles - hairless areas of skin (lips, fingertips) 3. Pacinian corpuscles - deep pressure (tendons, joints)
Temperature Senses
(warm and cold receptors)

10. 10.4 Special Senses Olfactory (smell) Gustatory (taste)
Hearing & Equilibrium
Sight

11. Sense of Smell (Olfactory)
Odor --> Receptor Cell  -->  Olfactory bulb --> Olfactory Tract 
--> LIMBIC SYSTEM
Aromatherapy....
Real or Bunk?

12. Sense of Taste (Gustatory)
Sweet
Sour
Bitter
Salty

13. What did the right eye say to the left eye?
Between you and me, something smells!

14. Sense of Hearing External Ear
Auricle (pinna) - outer ear External Auditory Meatus

15. Tympanic membrane - - vibrates to transmit sounds (like a telephone)
Ear wax – cerum

16. Middle Ear (tympanic cavity)
Eardrum (tympanum)
Auditory Ossicles - malleus, incus, stapes - transmit vibrations and amplify the signal
Auditory Tube (eustachian tube) - connects the middle ear to the throat - helps maintain air pressure
Eustachian tube shorter in children
Up and out
Down and in

17. The temporal bone houses the middle ear in a cavity less than 1 inch long
3 bones
Malleus – hammer shaped
Incus – anvil shaped
Staples – stirrup shaped

18. Semicircular Canals - sense of equilibrium Cochlea - sense or hearing
Inner Ear
Labyrinth - communicating chambers and tubes Osseous Labyrinth and Membranous Labyrinth Perilymph and Endolymph (fluids within the labyrinth)
Semicircular Canals - sense of equilibrium 
Cochlea - sense or hearing
Organ of Corti - contains hearing receptors, hair cells detect vibrations Organ of hearing

19. Why do children get tubes put in their ears?

20. Inner Ear: Cochlea
Inside the cochlea are special neurons called HAIR CELLS
The stapes is attached to the OVAL WINDOW, and vibrations cause the perilymph to vibrate; the hair cells here transmit this vibration.
Therefore the HAIR CELLS in this region are receptors for HEARING.
As you age, hair cells become damaged (loud music can speed this process along). Older people usually can’t hear frequencies that younger people can hear. Try the hearing test!

21. Steps in Hearing
1. Sound waves enter external auditory meatus 2. Eardrum vibrates 3. Auditory ossicles (malleus, incus, stapes) amplify vibrations 4. Stapes hits oval window and transmits vibrations to cochlea 5. Organs of corti contain receptor cells (hair cells) that deform from vibrations 6. Impulses sent to the vestibulocochlear nerve 7. Auditory cortex of the temporal lobe interprets sensory impulses 8. (Round window dissipates vibrations within the cochlea)

22. Decibel Level
Example of Noise
Dangerous Time
Lowest audible sound 30
Quiet library 50
Refrigerator noise 70
Noisy restaurant
Critical level 80
Factory noise
8 + hours 90
Shop tools
Impairment
100
Chain saws
< 2 hours
120
Rock concert
Immediate harm
140
Gunshot blast
Damage probable
180
Rocket launchpad
Permanent loss

23. Sense of Equilibrium
Static Equilibrium - sense the position of the head, maintain stability and posture
Dynamic Equilibrium (semicircular canals) - balance the head during sudden movement
Cerebellum - interprets impulses from the semicircular canals and maintains overall balance and stability

24. THE EYE
The eye is in the orbit of the skull for protection.
Within the orbit are 6 extrinsic eye muscles, which move the eye.
There are 4 cranial nerves: Optic (II), Occulomotor (III), Trochlear (IV), and Abducens (VI).
People of Asian descent have an EPICANTHIC FOLD in the upper eyelid; no functional difference.

25. THE EYEBALL Three layers of the eyeball Sclera Choroid Retina
What is the window of the eye Coronea Sclera – tough outer coat includes the cornea white of the eye
What does the middle layer contain – choroid (a dark pigment to prevent the scattering of incoming light rays)
Invlountary muscles – iris and ciliary muscles

26. Eyelid Covers and protects the eye, thin skin
Skin will not protect you from intense radiation, that’s why we use special goggles in a tanning bed

27. CONJUNCTIVA is like a covering around the eye and under the eyelids.
PINK EYE - also known as CONJUNCTIVITIS 
(from bacteria, very contagious)
Pink Eye Slide Show from Web MD

28. Lens
Transparent body behind the pupil focuses the light rays on the retina

29. Eye Fluids
Aqueous humor – watery fluid in the anterior chamber of the eye
Vitreous humor – jelly like fluid in the posterior chamber of the eye

30. LACRIMAL GLANDS are the largest set
LACRIMAL GLANDS are the largest set. They are on the superior lateral eyelid and they produce tears, which drain into the nasal cavity via the LACRIMAL DUCT.
The function is to moisten and lubricate the eye surface, and it has enzymes to kill bacteria (which thrive in warm, moist conditions).

31. Figure 16.5b

32. Outer Tunic Cornea - transparent, focuses light rays
Sclera – continuation of cornea, going toward the back of the eye (white of the eye)

33. Middle Tunic Choroid Coat – contains blood vessels
Ciliary Body – holds the lens in place
Lens – focusing
Iris – colored portion of the eye
Aqueous humor – liquid surrounding the lens
Pupil – opening for light to enter

34. Inner Tunic Retina - visual receptor cells
Fovea Centralis - region of the sharpest vision (aka, macula)
Optic Disc – where nerve fibers leave the eye, creating the blind spot
Vitreous Humor – supports internal parts, fluid

35. Figure 16.7a

36. Retina
The retina is made up of PHOTORECEPTORS, which are sensors for light.

37. Rods = monochromatic (b&w)
Cones  = color vision

40. We have difficult interpreting images that are upside down
Which one is the real mona lisa?

42. Fun Fact: -When you are looking at someone you love, your pupils dilate, and they do the same when you are looking at someone you hate.

43. What causes red-eye?
The flash on a camera is bright enough to cause a reflection off of the retina -- what you see is the red color from the blood vessels. Many cameras have a "red eye reduction" feature. In these cameras, the flash goes off twice -- once right before the picture is taken, and then again to actually take the picture. The first flash causes people's pupils to contract, reducing "red eye" 

44. Problems with the Eyes Cataracts Clouding of the lens leads to a clinical condition known as CATARACTS.  

45. Treatment is to remove the lens and replace it with a plastic one (which is not flexible either).

46. Why are all babies born with blue eyes?
Melanin is a brownish pigment that adds color to your hair, eyes, and skin. At the time babies are born, melanin hasn't yet been "deposited" in the eyes' iris. Hence, they appear blue. 
After about six months, eyes change color depending on the amount of melanin. If you have a lot of it, your eyes will turn dark brown.  If you have little, they'll stay blue. And if you have no melanin, your eyes may appear pink (albino). .

47. Colorblindness
A genetic trait that affects boys more than girls. The location of the gene is on the X chromosome

48. The region where the optic nerve and blood vessels goes in and out of the eye has no photoreceptors = BLIND SPOT.
Hold your hands out at 45° and that’s the location of the blind spot.
You can still see your hands because the other eye sees it. Close your right eye and look for your right hand and you’ll find the blind spot.

49. FLOATERS are when a capillary breaks and cells break off. 
Floaters don’t actually move, the eye just tries to track them.

50. HYPEROPIA (far-sighted) eyes are too short MYOPIA (nearsighted) eyes are too long

51. ASTIGMATISM
ASTIGMATISM is when the cornea has an irregular shape. Part of the field of view is out of focus.
They eyeball changes shape until age 24.

52. Lasik Surgery

53. See a real LASIK surgery (not for the squeamish)