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

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. Pathway of light entering the eye: Cornea  Pupil  Lens  Retina The cornea is the front portion of your eyeball

32. It is normally transparent (clear) If it becomes cloudy, you have a cataract

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 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

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

42. Astigmatism – distortion of image by cornea or lens

43. the retina contains rods and cones

44. 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

45. 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

46. 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

48. 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

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

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

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

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

53. 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

54. 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

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