Special Senses – Part I

1. Special Senses – Part I Chapter 8 BIO 160 Kelly Trainor

2. The Senses • General senses of touch • Temperature • Pressure • Pain • Special senses • Smell • Taste • Sight • Hearing • Equilibrium

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

4. 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

5. The Sense of Taste • Taste buds house the receptor organs • Location of taste buds • Most are on the tongue • Soft palate • Cheeks • The tongue is covered with projections called papillae • Taste buds are found on the sides of papillae • Gustatory cells are the receptors • Have gustatory hairs (long microvilli) • Hairs are stimulated by chemicals dissolved in saliva

6. Taste Buds Figure 8.18

7. Taste Sensations • Sweet receptors (sugars) • Saccharine • Some amino acids • Sour receptors • Acids • Bitter receptors • Alkaloids • Salty receptors • Metal ions

8. Special Senses – Part II Chapter 8 BIO 160 Kelly Trainor

9. The Eye and Vision • 70% of all sensory receptors are in the eyes • Each eye has over a million nerve fibers • Protection for the eye • Most of the eye is enclosed in a bony orbit • A cushion of fat surrounds most of the eye

10. Accessory Structures of the Eye • Eyelids and eyelashes • Conjunctiva • Lacrimal apparatus • Extrinsic eye muscles

11. Accessory Structures of the Eye • Eyelids and eyelashes • Tarsal glands lubricate the eye • Ciliary glands are located between the eyelashes • Conjunctiva • Membrane that lines the eyelids • Connects to the surface of the eye • Secretes mucus to lubricate the eye

12. Accessory Structures of the Eye • Function of the lacrimal apparatus • Protects, moistens, and lubricates the eye • Empties into the nasal cavity • Properties of lacrimal fluid • Dilute salt solution (tears) • Contains antibodies and lysozyme

13. Accessory Structures of the Eye • Extrinsic eye muscles • Six muscles attach to the outer surface of the eye • Produce eye movements

14. Structure of the Eye • Layers forming the wall of the eyeball • Fibrous layer • Outside layer • Vascular layer • Middle layer • Sensory layer • Inside layer

15. Structure of the Eye Figure 8.4a

16. Structure of the Eye Figure 8.4b

17. Structure of the Eye: The Fibrous Layer • Sclera • White connective tissue layer • Seen anteriorly as 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

18. Structure of the Eye: Vascular Layer • Choroid is a blood-rich nutritive layer in the posterior of the eye • Pigment prevents light from scattering • Modified anteriorly into two structures • Ciliary body—smooth muscle attached to lens • Iris—regulates amount of light entering eye • Pigmented layer that gives eye color • Pupil—rounded opening in the iris

19. Structure of the Eye: Sensory Layer • Retina contains two layers • Outer pigmented layer • Inner neural layer • Contains receptor cells (photoreceptors) • Rods • Cones

20. Structure of the Eye: Sensory Layer • Signals pass from photoreceptors via a two-neuron chain • Signals leave the retina toward the brain through the optic nerve • Optic disc (blind spot) is where the optic nerve leaves the eyeball • Cannot see images focused on the optic disc

21. Structure of the Eye: Sensory Layer Figure 8.5b

22. Structure of the Eye: Sensory Layer • Neurons of the retina and vision • Rods • Most are found towards the edges of the retina • Allow dim light vision and peripheral vision • All perception is in gray tones • Cones • Allow for detailed color vision • Densest in the center of the retina • Fovea centralis—area of the retina with only cones • Cone sensitivity • Three types of cones • Different cones are sensitive to different wavelengths • Color blindness is the result of the lack of one cone type • No photoreceptor cells are at the optic disc, or blind spot

23. Structure of the Eye: Sensory Layer

24. Lens • Biconvex crystal-like structure • Held in place by a suspensory ligament attached to the ciliarybody • Cataracts result when the lens becomes hard and opaque with age • Vision becomes hazy and distorted • Eventually causes blindness in affected eye

25. Lens

26. Two Segments, or Chambers, of the Eye • Anterior (aqueous) segment • Anterior to the lens • Contains aqueous humor • Posterior (vitreous) segment • Posterior to the lens • Contains vitreous humor

27. Anterior Segment • Aqueous humor • Watery fluid found between lens and cornea • Similar to blood plasma • Helps maintain intraocular pressure • Provides nutrients for the lens and cornea • Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm • Vitreous humor • Gel-like substance posterior to the lens • Prevents the eye from collapsing • Helps maintain intraocular pressure

28. Pathway of Light Through the Eye • Light must be focused to a point on the retina for optimal vision • The eye is set for distance vision (over 20 feet away) • Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away)

29. Pathway of Light Through the Eye • Image formed on the retina is a real image • Real images are • Reversed from left to right • Upside down • Smaller than the object

30. A Closer Look • Emmetropia—eye focuses images correctly on the retina • Myopia (nearsighted) • Distant objects appear blurry • Light from those objects fails to reach the retina and are focused in front of it • Results from an eyeball that is too long • Hyperopia (farsighted) • Near objects are blurry while distant objects are clear • Distant objects are focused behind the retina • Results from an eyeball that is too short or from a “lazy lens” • Astigmatism • Images are blurry • Results from light focusing as lines, not points, on the retina due to unequal curvatures of the cornea or lens

31. Homeostatic Imbalances of the Eyes • Night blindness—inhibited rod function that hinders the ability to see at night • Color blindness—genetic conditions that result in the inability to see certain colors • Due to the lack of one type of cone (partial color blindness) • Cataracts—when lens becomes hard and opaque, our vision becomes hazy and distorted • Glaucoma—can cause blindness due to increasing pressure within the eye

32. Special Senses – Part III Chapter 8 BIO 160 Kelly Trainor

33. The Ear • Houses two senses • Hearing • Equilibrium (balance) • Receptors are mechanoreceptors • Different organs house receptors for each sense

34. Anatomy of the Ear • The ear is divided into three areas • External (outer) ear • Middle ear (tympanic cavity) • Inner ear (bony labyrinth)

35. Anatomy of the Ear Figure 8.12

36. The External Ear • Involved in hearing only • Structures of the external ear • Auricle (pinna) • External acoustic meatus (auditory canal) • Narrow chamber in the temporal bone • Lined with skin and ceruminous (wax) glands • Ends at the tympanic membrane

37. The Middle Ear (Tympanic Cavity) • Air-filled cavity within the temporal bone • Only involved in the sense of hearing • Two tubes are associated with the inner ear • The opening from the auditory canal is covered by the tympanic membrane • 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 Middle Ear (Tympanic Cavity) • Three bones (ossicles) span the cavity • Malleus (hammer) • Incus (anvil) • Stapes (stirrip) • Function • Vibrations from eardrum move the malleus  anvil  stirrup  inner ear

39. Anatomy of the Ear Figure 8.12

40. Inner Ear or Bony Labyrinth • Includes sense organs for hearing and balance • Filled with perilymph • A maze of bony chambers within the temporal bone • Cochlea • Vestibule • Semicircular canals

41. Anatomy of the Ear Figure 8.12

42. Organs of Equilibrium • Equilibrium receptors of the inner ear are called the vestibular apparatus • Vestibular apparatus has two functional parts • Static equilibrium • Dynamic equilibrium

43. Static Equilibrium • Maculae—receptors in the vestibule • Report on the position of the head • Hair cells are embedded in the otolithic membrane • Otoliths (tiny stones) float in a gel around the hair cells • Movements cause otoliths to bend the hair cells

44. Structure and Function of Maculae Figure 8.13a

45. Dynamic Equilibrium • Cristaampullaris—receptors in the semicircular canals • Tuft of hair cells • Cupula (gelatinous cap) covers the hair cells • Action of angular head movements • The cupula stimulates the hair cells • An impulse is sent via the vestibular nerve to the cerebellum • Action of angular head movements • The cupula stimulates the hair cells • An impulse is sent via the vestibular nerve to the cerebellum

46. Organs of Equilibrium

47. Organs of Hearing • Organ of Corti • Located within the cochlea • Receptors = hair cells on the basilar membrane • Gel-like tectorial membrane is capable of bending hair cells • Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

48. Organs of Hearing Figure 8.15a

49. Organs of Hearing Figure 8.15b

50. Mechanism of Hearing • Vibrations from sound waves move tectorial membrane • Hair cells are bent by the membrane • An action potential starts in the cochlear nerve • Continued stimulation can lead to adaptation