1. The Sense Organs

2. Humans react to both internal and external stimuli – we can detect these stimuli because our bodies contain several types of sensory receptors

3. Sensory Receptors – neurons that respond to changes in the environment (stimuli)
Classified by stimuli type:
1. Mechanoreceptors – detect mechanical force (movement, pressure, or touch)

4. 2. Photoreceptors – detect light energy
3. Chemoreceptors – detect chemical changes
4. Thermoreceptors – detect temperature changes
5. Nociceptors – detect harmful stimuli, respond to pain

5. Sensory organs – these are specialized structures that contain sensory receptors
There are 5 major sensory organs:
Ear – contains mechanoreceptors
Eyes – contain photoreceptors
Nose – contains chemoreceptors

6. Mouth – contains chemoreceptors
Skin – contains mechanoreceptors and thermoreceptors
Nociceptors – are found everywhere except the brain

7. Classified by location:
1. exteroceptors – stimuli outside of the body
found near or at the body surface
include touch, pressure, pain, and temperature receptors in the skin and most receptors of sense organs

8. 2. Interoceptors – stimuli within the body
monitor chemical changes, tissue stretch, and temperature
their activity can cause pain, discomfort, hunger, or thirst …
usually unaware of their workings

9. 3. Proprioceptors – specialized neurons found in skeletal muscles, ligaments, tendons and joints
location is much more restricted
constantly advise the brain of body movements

10. 1. Ears are the sense organs responsible for hearing and balance (equilibrium)
The ear is divided into 3 regions:
outer ear
middle ear
inner ear

11. The outer ear is made up of:
Auricle – projecting portion composed of cartilage
Ear canal – tube that leads down to the eardrum

12. The outer ear is separated from the middle ear by the eardrum

13. The middle ear is an air-filled cavity that is connected to the pharynx by a tiny tube called the Eustachian tube

14. the function of this tube is to equalize pressure on both sides of the eardrum, preventing it from rupturing

15. Example – when you go up in an airplane, the outside pressure decreases
Air leaves the middle ear through the Eustachian tube until the pressure in the middle ear matches the outside air pressure

16. The middle ear contains 3 tiny ear bones called ossicles
the ossicles are the tiniest bones in the body
they function to transfer vibrations from the eardrum to the inner ear

18. The inner ear contains a coiled structure called the cochlea and 3 semicircular canals

19. The cochlea contains hair cells (mechanoreceptors) that receive vibrations from the ossicles and transmits that information through the vestibulocochlear nerve to the region of the cerebrum that interprets sounds

20. The semicircular canals contain hair cells (mechanoreceptors) that detect rotation of the head

21. they send this information through the vestibulocochlear nerve to the region of the brain that maintains balance (cerebellum)

22. sometimes the hair cells of the semicircular canals are overstimulated – when this happens you experience nausea…you are suffering from motion sickness

23. 2. Eyes are the sense organs responsible for sight

24. The eye is made up of 3 layers:
Sclera – white of the eye (tough, outer part of the eye)
Choroid – black layer that keeps interior of eye dark
Inner retina – contains photoreceptors

28. There are 2 types of photoreceptors found in the retina:
rods
cones

29. Rods contain the pigment rhodopsin, which is stimulated by weak light
rods enable you to see shades of gray but not colors
they produce poorly defined images

30. Cones contain the pigment photopsin that is stimulated by bright light
they enable you to see sharp images and in color
If your cones are nonfunctional you are colorblind and see only in shades of gray

31. The cornea is the front portion of your eyeball
It is normally transparent (clear)

32. Pathway of light entering the eye:
Cornea 
Pupil 
Lens 
Retina

33. The pupil is the tiny black opening in the center of your iris (colored portion of your eye)
The iris constricts the pupil (gets smaller) when you are exposed to bright light

34. this reduces the amount of light entering the eye

35. The iris dilates the pupil when you are exposed to dim light
this allows more light to enter the eye

36. The lens functions to focus images on the retina

37. If it becomes cloudy, you have a cataract

38. if the lens fails to focus images properly, you need glasses
You are: Hyperopia “Farsightedness”
Farsighted if you can see far away, but objects close to you are blurred

40. You are: Myopia “Nearsightedness”
Nearsighted if you can see close to you, but objects far away are blurred

43. Astigmatism – distortion of image by cornea or lens

44. the retina contains rods and cones

45. you have fewer cones than rods
most cones are located in the back portion of the retina, while most rods are found around the periphery

46. The fovea is a tiny pit in the very back of the eye that contains cones only
your vision is sharpest when the lens focuses the image on the fovea

47. There is one area of the retina which contains no cones or rods
this area is called the blind spot
there are not cones or rods in this area because this is where the optic nerve enters the eye

49. When the rods and cones have been stimulated, they send impulses through the optic nerve, to the occipital lobe of the cerebrum to be interpreted

50. 3. Your tongue is the sense organ responsible for taste

51. The receptors for taste are chemoreceptors that are located in the taste buds

52. When food dissolves on your tongue, chemicals are released that stimulate chemoreceptors
they send impulses to the cerebrum to be interpreted

53. Despite the many flavors we taste, there are only tastes that stimulate your taste buds:
sweet
umami - savoriness as in beef or other protein rich foods
sour
salty
bitter
Other flavors are perceived by your sense of smell (80% of taste is smell)

54. The taste buds that detect sweet, sour, bitter, and salty flavors are found in certain areas of the tongue
sweet - tip
sour - sides
bitter - back
salty – over the entire surface of the tongue

55. 4. Your nose is the sense organ responsible for smell
the receptors for smell are chemoreceptors which are located in the roof of the nasal cavity
the odors we breathe contain numerous chemicals

56. these chemicals stimulate the chemoreceptors, which send impulses through the olfactory nerve to the cerebrum to be interpreted