1. The Senses Special senses Smell Taste Sight Hearing Equilibrium

2. © 2012 Pearson Education, Inc. The Eye and Vision 70 percent 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

3. © 2012 Pearson Education, Inc. Accessory Structures of the Eye Eyelids and eyelashes Conjunctiva Lacrimal apparatus Extrinsic eye muscles

4. © 2012 Pearson Education, Inc. Figure 8.1 Site where conjunctiva merges with cornea Palpebral fissure Lateral commissure (canthus) Iris Eyelid Eyebrow Eyelid Eyelashes Pupil Lacrimal caruncle Medial commissure (canthus) Sclera (covered by conjunctiva)

5. © 2012 Pearson Education, Inc. Accessory Structures of the Eye Eyelids Meet at the medial and lateral commissure (canthus) Eyelashes Tarsal glands produce an oily secretion that lubricates the eye Ciliary glands are located between the eyelashes

6. © 2012 Pearson Education, Inc. Accessory Structures of the Eye Conjunctiva Membrane that lines the eyelids Connects to the outer surface of the eye Secretes mucus to lubricate the eye and keep it moist

7. © 2012 Pearson Education, Inc. Accessory Structures of the Eye Lacrimal apparatus = lacrimal gland + ducts Lacrimal gland—produces lacrimal fluid; situated on lateral aspect of each eye Lacrimal canaliculi—drain lacrimal fluid from eyes medially Lacrimal sac—provides passage of lacrimal fluid towards nasal cavity Nasolacrimal duct—empties lacrimal fluid into the nasal cavity

8. © 2012 Pearson Education, Inc. Figure 8.2a Lacrimal gland (a) Conjunctiva Anterior aspect Eyelid Eyelashes Tarsal glands Eyelid Excretory duct of lacrimal gland

9. © 2012 Pearson Education, Inc. Figure 8.2b Lacrimal gland Excretory ducts of lacrimal gland Lacrimal canaliculus Nasolacrimal duct Inferior meatus of nasal cavity Nostril Lacrimal sac (b)

10. © 2012 Pearson Education, Inc. Accessory Structures of the Eye Function of the lacrimal apparatus Protects, moistens, and lubricates the eye Empties into the nasal cavity Lacrimal secretions (tears) contain: Dilute salt solution Mucus Antibodies Lysozyme (enzyme that destroys bacteria)

11. © 2012 Pearson Education, Inc. Accessory Structures of the Eye Extrinsic eye muscles Six muscles attach to the outer surface of the eye Produce eye movements

12. © 2012 Pearson Education, Inc. Figure 8.3a Superior oblique muscle Superior oblique tendon Superior rectus muscle Conjunctiva Lateral rectus muscle Optic nerve Inferior rectus muscle Inferior oblique muscle (a)

13. © 2012 Pearson Education, Inc. Figure 8.3b Trochlea Superior oblique muscle Medial rectus muscle Lateral rectus muscle Superior oblique tendon Superior rectus muscle (b) Inferior rectus muscle Axis at center of eye

14. © 2012 Pearson Education, Inc. Figure 8.3c

15. © 2012 Pearson Education, Inc. Structure of the Eye Layers forming the wall of the eyeball Fibrous layer Outside layer Vascular layer Middle layer Sensory layer Inside layer

16. © 2012 Pearson Education, Inc. Figure 8.4a Ciliary body Ciliary zonule Cornea Iris Pupil Lens Sclera Choroid Retina Fovea centralis Optic nerve (a) Aqueous humor (in anterior segment) Scleral venous sinus (canal of Schlemm) Optic disc (blind spot) Central artery and vein of the retina Vitreous humor (in posterior segment)

17. © 2012 Pearson Education, Inc. Figure 8.4b Ciliary body Iris Lens Cornea Ciliary zonule (b) Retina Choroid Sclera Fovea centralis Optic disc Optic nerve Margin of pupil Aqueous humor (in anterior segment) Vitreous humor in posterior segment

18. © 2012 Pearson Education, Inc. 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

19. © 2012 Pearson Education, Inc. 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

20. © 2012 Pearson Education, Inc. Structure of the Eye: Sensory Layer Retina contains two layers Outer pigmented layer Inner neural layer Contains receptor cells (photoreceptors) Rods Cones

21. © 2012 Pearson Education, Inc. Structure of the Eye: Sensory Layer Signals pass from photoreceptors via a two- neuron chain Bipolar neurons Ganglion cells 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

22. © 2012 Pearson Education, Inc. Figure 8.5a Rod Cone (a) Pathway of light Pigmented layer of retina Bipolar cells Ganglion cells

23. © 2012 Pearson Education, Inc. Figure 8.5b Pigmented layer of retina Neural layer of retina Central artery and vein of retina Optic disc Optic nerve (b) Sclera Choroid

24. © 2012 Pearson Education, Inc. 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

25. © 2012 Pearson Education, Inc. Structure of the Eye: Sensory Layer Neurons of the retina and vision Cones Allow for detailed color vision Densest in the center of the retina Fovea centralis–lateral to blind spot Area of the retina with only cones Visual acuity (sharpest vision) is here No photoreceptor cells are at the optic disc, or blind spot

26. © 2012 Pearson Education, Inc. Structure of the Eye: Sensory Layer 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

27. © 2012 Pearson Education, Inc. Figure 8.6 560 nm (red cones) 530 nm (green cones) 420 nm (blue cones) Light absorption by cone populations 380 450500550600650700750 Wavelengths (nanometers)

28. © 2012 Pearson Education, Inc. Lens Biconvex crystal-like structure Held in place by a suspensory ligament attached to the ciliary body

29. © 2012 Pearson Education, Inc. Figure 8.4a Ciliary body Ciliary zonule Cornea Iris Pupil Lens Sclera Choroid Retina Fovea centralis Optic nerve (a) Aqueous humor (in anterior segment) Scleral venous sinus (canal of Schlemm) Optic disc (blind spot) Central artery and vein of the retina Vitreous humor (in posterior segment)

30. © 2012 Pearson Education, Inc. Lens Cataracts result when the lens becomes hard and opaque with age Vision becomes hazy and distorted Eventually causes blindness in affected eye Risk factors include: Diabetes mellitus Frequent exposure to intense sunlight Heavy smoking

31. © 2012 Pearson Education, Inc. Figure 8.7

32. © 2012 Pearson Education, Inc. 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

33. © 2012 Pearson Education, Inc. Figure 8.4a Ciliary body Ciliary zonule Cornea Iris Pupil Lens Sclera Choroid Retina Fovea centralis Optic nerve (a) Aqueous humor (in anterior segment) Scleral venous sinus (canal of Schlemm) Optic disc (blind spot) Central artery and vein of the retina Vitreous humor (in posterior segment)

34. © 2012 Pearson Education, Inc. 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

35. © 2012 Pearson Education, Inc. Posterior Segment Vitreous humor Gel-like substance posterior to the lens Prevents the eye from collapsing Helps maintain intraocular pressure

36. © 2012 Pearson Education, Inc. Ophthalmoscope Instrument used to illuminate the interior of the eyeball Can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina

37. © 2012 Pearson Education, Inc. Figure 8.8 Fovea centralis Macula Blood vessels Optic disc Retina Lateral Medial

38. © 2012 Pearson Education, Inc. 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)

39. © 2012 Pearson Education, Inc. Figure 8.9 Retina Focal point Light from distant source (a) Light from near source Focal point Retina (b)

40. © 2012 Pearson Education, Inc. 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

41. © 2012 Pearson Education, Inc. Figure 8.10

42. © 2012 Pearson Education, Inc. Visual Fields and Visual Pathways Optic chiasma Location where the optic nerves cross Fibers from the medial side of each eye cross over to the opposite side of the brain Optic tracts Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye

43. © 2012 Pearson Education, Inc. Figure 8.11 Fixation point Right eye Left eye Optic chiasma Optic nerve Optic tract Optic radiation Occipital lobe (visual cortex) Thalamus

44. © 2012 Pearson Education, Inc. Eye Reflexes Internal muscles are controlled by the autonomic nervous system Bright light causes pupils to constrict through action of radial, circular, and ciliary muscles Viewing close objects causes accommodation External muscles control eye movement to follow objects Viewing close objects causes convergence (eyes moving medially)

45. © 2012 Pearson Education, Inc. 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

46. © 2012 Pearson Education, Inc. A Closer Look 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”

47. © 2012 Pearson Education, Inc. Focal plane (a) Emmetropic eye Correction None required Concave lens Convex lens (b) Myopic eye (nearsighted) (c) Hyperopic eye (farsighted)

48. © 2012 Pearson Education, Inc. A Closer Look Astigmatism Images are blurry Results from light focusing as lines, not points, on the retina due to unequal curvatures of the cornea or lens

49. © 2012 Pearson Education, Inc. 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

50. © 2012 Pearson Education, Inc. Homeostatic Imbalances of the Eyes Glaucoma—can cause blindness due to increasing pressure within the eye Hemianopia—loss of the same side of the visual field of both eyes; results from damage to the visual cortex on one side only

51. © 2012 Pearson Education, Inc. The Ear Houses two senses Hearing Equilibrium (balance) Receptors are mechanoreceptors Different organs house receptors for each sense

52. © 2012 Pearson Education, Inc. Anatomy of the Ear The ear is divided into three areas External (outer) ear Middle ear (tympanic cavity) Inner ear (bony labyrinth)

53. © 2012 Pearson Education, Inc. Figure 8.12 Auricle (pinna) External (outer) ear Middle ear Internal (inner) ear Oval window Vestibule Round window Hammer (malleus) Anvil (incus) Stirrup (stapes) Auditory ossicles Semicircular canals Pharyngotympanic (auditory) tube Cochlea External acoustic meatus (auditory canal) Tympanic membrane (eardrum) Vestibulocochlear nerve

54. © 2012 Pearson Education, Inc. 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

55. © 2012 Pearson Education, Inc. The Middle Ear (Tympanic Cavity) Air-filled cavity within the temporal bone Only involved in the sense of hearing

56. © 2012 Pearson Education, Inc. The Middle Ear (Tympanic Cavity) 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

57. © 2012 Pearson Education, Inc. Bones of the Middle Ear (Tympanic Cavity) Three bones (ossicles) span the cavity Malleus (hammer) Incus (anvil) Stapes (stirrup) Function Vibrations from eardrum move the hammer  anvil  stirrup  inner ear

58. © 2012 Pearson Education, Inc. Figure 8.12 Auricle (pinna) External (outer) ear Middle ear Internal (inner) ear Oval window Vestibule Round window Hammer (malleus) Anvil (incus) Stirrup (stapes) Auditory ossicles Semicircular canals Pharyngotympanic (auditory) tube Cochlea External acoustic meatus (auditory canal) Tympanic membrane (eardrum) Vestibulocochlear nerve

59. © 2012 Pearson Education, Inc. Inner Ear or Bony Labyrinth Includes sense organs for hearing and balance Filled with perilymph Contains a maze of bony chambers within the temporal bone Cochlea Vestibule Semicircular canals

60. © 2012 Pearson Education, Inc. Figure 8.12 Auricle (pinna) External (outer) ear Middle ear Internal (inner) ear Oval window Vestibule Round window Hammer (malleus) Anvil (incus) Stirrup (stapes) Auditory ossicles Semicircular canals Pharyngotympanic (auditory) tube Cochlea External acoustic meatus (auditory canal) Tympanic membrane (eardrum) Vestibulocochlear nerve

61. © 2012 Pearson Education, Inc. Organs of Equilibrium Equilibrium receptors of the inner ear are called the vestibular apparatus Vestibular apparatus has two functional parts Static equilibrium Dynamic equilibrium

62. © 2012 Pearson Education, Inc. Figure 8.14a Semicircular canals Ampulla Vestibular nerve Vestibule (a)

63. © 2012 Pearson Education, Inc. Static Equilibrium Maculae—receptors in the vestibule Report on the position of the head Send information via the vestibular nerve Anatomy of the maculae 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

64. © 2012 Pearson Education, Inc. Figure 8.13a Membranes in vestibule Otoliths Hair tuft (a) Hair cell Supporting cell Otolithic membrane Nerve fibers of vestibular division of cranial nerve VIII

65. © 2012 Pearson Education, Inc. Figure 8.13b Force of gravity Otoliths Hair cell Head upright (b) Head tilted Otolithic membrane

66. © 2012 Pearson Education, Inc. Dynamic Equilibrium These receptors respond to angular or rotary movements Crista ampullaris (in the ampulla of each semicircular canal)—dynamic equilibrium receptors are located in the semicircular canals Tuft of hair cells covered with cupula (gelatinous cap) If the head moves, the cupula drags against the endolymph

67. © 2012 Pearson Education, Inc. Figure 8.14a Semicircular canals Ampulla Vestibular nerve Vestibule (a)

68. © 2012 Pearson Education, Inc. Figure 8.14b-c (b) Cupula of crista ampullaris Endolymph Ampulla Flow of endolymph Cupula Direction of body movement (c) Nerve fibers

69. © 2012 Pearson Education, Inc. Dynamic Equilibrium Action of angular head movements The movement of the cupula stimulates the hair cells An impulse is sent via the vestibular nerve to the cerebellum

70. © 2012 Pearson Education, Inc. 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

71. © 2012 Pearson Education, Inc. Figure 8.15a Spiral organ of Corti Temporal bone Perilymph in scala vestibuli Perilymph in scala tympani (a) Vestibular membrane Afferent fibers of the cochlear nerve Cochlear duct (contains endolymph) Temporal bone

72. © 2012 Pearson Education, Inc. Figure 8.15b (b) Hair (receptor) cells of spiral organ of Corti Tectorial membrane Vestibular membrane Basilar membrane Supporting cells Fibers of the cochlear nerve

73. © 2012 Pearson Education, Inc. 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 Impulse travels to the temporal lobe Continued stimulation can lead to adaptation

74. © 2012 Pearson Education, Inc. Figure 8.16 EXTERNAL EAR Pinna Auditory canal Ear- drum Hammer, anvil, stirrup MIDDLE EAR Oval window INTERNAL EAR Fluids in cochlear canals Upper and middlelower Time Spiral organ of Corti stimulated Amplification in middle ear Amplitude One vibration Pressure

75. © 2012 Pearson Education, Inc. Mechanism of Hearing High-pitched sounds disturb the short, stiff fibers of the basilar membrane Receptor cells close to the oval window are stimulated Low-pitched sounds disturb the long, floppy fibers of the basilar membrane Specific hair cells further along the cochlea are affected

76. © 2012 Pearson Education, Inc. Figure 8.17 Stapes Scala vestibuli Fibers of sensory neurons Perilymph Oval window Round window Scala tympani Basilar membrane Cochlear duct Fibers of basilar membrane Base (short, stiff fibers) Apex (long, floppy fibers) 20,000 (High notes) 2,000 200 Frequency (Hz) (a) (b) 20 (Low notes)

77. © 2012 Pearson Education, Inc. 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

78. © 2012 Pearson Education, Inc. Figure 8.18 Olfactory bulb Olfactory tract Mucus layer (a) (b) Supporting cell Olfactory receptor cell Olfactory hairs (cilia) Route of inhaled air containing odor molecules Cribriform plate of ethmoid bone Olfactory filaments of the olfactory nerve Olfactory mucosa

79. © 2012 Pearson Education, Inc. The Sense of Taste Taste buds house the receptor organs Location of taste buds Most are on the tongue Soft palate Cheeks

80. © 2012 Pearson Education, Inc. Figure 8.19a Epiglottis Palatine tonsil Lingual tonsil Fungiform papillae (a)

81. © 2012 Pearson Education, Inc. Figure 8.19b Circumvallate papilla Taste buds (b)

82. © 2012 Pearson Education, Inc. The Tongue and Taste The tongue is covered with projections called papillae Filiform papillae—sharp with no taste buds Fungiform papillae—rounded with taste buds Circumvallate papillae—large papillae with taste buds Taste buds are found on the sides of papillae

83. © 2012 Pearson Education, Inc. Structure of Taste Buds Gustatory cells are the receptors Have gustatory hairs (long microvilli) Hairs are stimulated by chemicals dissolved in saliva

84. © 2012 Pearson Education, Inc. Structure of Taste Buds Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas Facial nerve Glossopharyngeal nerve Vagus nerve

85. © 2012 Pearson Education, Inc. Taste Sensations Sweet receptors (sugars) Saccharine Some amino acids Sour receptors Acids Bitter receptors Alkaloids Salty receptors Metal ions

86. © 2012 Pearson Education, Inc. Developmental Aspects of the Special Senses Formed early in embryonic development Eyes are outgrowths of the brain All special senses are functional at birth

87. © 2012 Pearson Education, Inc. 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

88. © 2012 Pearson Education, Inc. Developmental Aspects of the Special Senses Eye problems Strabismus—“crossed eyes” results from unequal pulls by the external eye muscles in babies Ophthalmia neonatorum—conjunctivitis resulting from mother having gonorrhea. Baby’s eyelids are swollen and pus is produced

89. © 2012 Pearson Education, Inc. Developmental Aspects of the Special Senses Eye problems Presbyopia—“old vision” results from decreasing lens elasticity that accompanies aging

90. © 2012 Pearson Education, Inc. Developmental Aspects of the Special Senses Ear problems Presbycusis—type of sensorineural deafness Otosclerosis—ear ossicles fuse