Special Senses: Olfaction, Gustation, Vision, and Hearing

1. Exercise 17 Special Senses Portland Community College BI 232

2. Special Senses • Sensory receptors are extensions of the nervous system • Contain specialized cells or processes that relay specific information • A receptor must convert the stimulus to an action potential (transductions) • The AP must be conducted from the receptor to the CNS

3. General and Special senses • General senses include touch, pressure, vibration, pain, temperature, proprioception and chemical and fluid pressure. • Special senses include olfaction, gustation, vision and hearing and equilibrium

4. Olfaction • Sensory receptors for olfaction are located in the olfactory epithelium consists of: • Olfactory receptor cells • Supporting cells • Basal cells

5. Testing olfactory adaptation • Adaptation refers to a decreasing sensitivity to a stimulus over time. • Sensitivity to an odor diminishes over time. • Do Activity 17.2

6. Gustation • Sensory receptors for gustation are located in taste buds • Located mainly on the top of the tongue but also in other areas of mouth • Innervated by cranial nerves VII, IX and X

7. Lingual Papilla • Papilla are epithelial projections on the superior surface of the tongue • Circumvallate papilla contain about 100 taste buds • Fungiform papilla contain about 5 -10 taste buds • Filiform papillae provide friction that helps the tongue move objects around in the mouth, but do not contain taste buds

9. Taste Receptors • Taste buds contain spindle-shaped cells • Basal cells: produce daughter cells that mature in stages • Gustatory cells: extend microvilli into the surrounding fluids through a taste pore • Contain the taste receptors

10. Taste Bud Histology

11. Gustatory Discrimination • Umami: “Beef” • Salty • Sweet • Bitter • Sour • Substances must be dissolved (saliva) for the chemically gated ion channels to open • Olfaction is very important in taste

12. Lab Activities • Look at the modes that show oral structures • Look at slides of taste buds. • Do activity 17.4: Parts A and B

13. Lab Activity 17 Vision

16. Histology of the Retina

17. Ciliary body A • Ciliary processes • Ciliary epithelium • Secretes aqueous humor • Ciliary muscle - (intrinsic eye muscle) • Suspensory ligament of the lens A= anterior chamber P= posterior chamber P 3 1 2

19. Neural pathway for vision • After optic nerves exit the eyeballs they meet at the optic chiasm. • Fibers from medial half of retina cross over to the opposite side. • Optic tracts project to the lateral geniculate bodies in thalamus • Some fibers are relayed to superior colliculi

20. Lacrimal Apparatus • Consists of the lacrimal gland and its accessory structures. • Produces water, alkaline tears. • Contain antibacterial enzyme called lysozyme for protection from bacterial infections

21. Extrinsic Eye Muscles • Superior oblique: primarily rotates the top of the eye toward the nose and secondarily moves the eye downward • Trochlea: Ligament sling • Superior rectus: primarily moves the eye upward and secondarily rotates the top of the eye toward the nose • Lateral rectus: moves the eye away from the nose

22. Extrinsic Eye Muscles • Medial rectus: moves the eye toward the nose • Inferior oblique: primarily rotates the top of the eye away from the nose and secondarily moves the eye upward • Inferior rectus: primarily moves the eye downward and secondarily rotates the top of the eye away from the nose

23. Ear Nose

24. Extrinsic Eye Muscles

25. Refraction • Light is bent when it passes from one medium to another medium with a different density • Light passes through these before it hits the retina: • Cornea • Aqueous humor • Lens • Vitreous humor

26. Focal Point & Focal Distance • Focal Point: The specific point of intersection on the retina. • Focal distance: The distance between the center of the lens and its focal point. Determined by two factors: • Distance from the object to the lens • Shape of the lens

27. Focal Distance • Distance from the object to the lens: the closer an object is, the greater the focal distance • Shape of the lens: the rounder the lens, the more refraction occurs, so it has a shorter focal distance

28. Accommodation • Accommodation is an alteration in the curvature of the lens of the eye to focus an image on the retina • Near objects: Lens becomes rounder • Distance objects: Lens becomes flatter

29. Accommodation • Emmetropia is normal vision. • The image will be focused on the retina’s surface

30. Accommodation Problems • Myopia: Nearsighted • The eyeball is too deep or the curvature of the lens is too great • The focal point is in front of the retina, so distance objects are blurry • Corrected with a diverging lens

31. Accommodation Problems • Hyperopia: Farsighted • The eyeball is too shallow or the curvature of the lens is too flat • The focal point is behind of the retina, so near objects are blurry • Corrected with a converging lens

32. Astigmatism • The degree of curvature in the cornea or lens varies from one axis to another (is uneven or wavy) • This causes light to focus on more than one area of the retina creating a blurry image.

33. Intrinsic Eye Muscles of the Iris • Pupils constrict (Parasympathetic) • Close vision and bright light • Pupils dilate (Sympathetic) • Distant vision and dim light

34. Color Blindness • Cones are responsible for color vision. • 3 types of cones each able to absorb light at specific wavelengths. • Lack of one or more types of cone can cause color blindness • Use Ishihara color plates to test

35. Activities • Dissect cow eye • Perform visual tests

36. Lab Activity 18 Hearing & Equilibrium

37. Vestibular Portion Cochlear Portion

39. Middle Ear Ossicles (Bones) Incus Malleus Stapes

40. The stapes strikes the oval window of the cochlea

41. Vestibular Complex

42. Cochlea

43. Cochlea Uncoiled vestibular duct oval window helicotrema round window tympanic duct Cochlear duct containing the Organ of Corti • Stapes pushes on fluid of vestibular duct at oval window • At helicotrema, vibration moves into tympanic duct • Fluid vibration dissipated at round window which bulges • The central structure is vibrated (cochlear duct)

44. Organ of Corti

45. Neural pathways for hearing • Vestibulocochlear nerve (CN VIII) has 2 divisions: • Vestibular division-send impulses to medulla where fibers are crossed and uncrossed to travel to the cerebellum; to the cortex

46. Neural pathways for hearing • The cochlear division receive impulses to the cochlear nuclei in the medulla. • Some fibers cross over to other side. • Some remain on the same side. • Both synapse in the inferior colliculi

47. Types of Hearing Loss • Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the bones of the middle ear. • Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain.

48. Weber & Rinne Tests • Weber test: determines if hearing loss is present in one ear, but does not distinguish conductive and sensorineural deafness • Rinne test : Evaluates an individual’s ability to hear sounds conducted by air or bone • Used together, these test can distinguish between the two types of hearing loss

49. Weber Test • Ring tuning fork and place on center of head. Ask the subject where they hear the sound. • Interpreting the test: • Normally, the sound is heard in the center of the head or equally in both ears. • Sound localizes toward the poor ear with a conductive loss • Sound localizes toward the good ear with a sensorineural hearing loss

50. Rinne Test • Place the vibrating tuning fork on the base of the mastoid bone. • Ask patient to tell you when the sound is no longer heard. • Immediately move the tuning fork to the front of the ear • Ask the patient to tell you when the sound is no longer heard. • Repeat the process putting the tuning fork in front of the ear first