1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 15 The Special Senses: Part A

2. Copyright © 2010 Pearson Education, Inc. The Eye and Vision 70% of all sensory receptors are in the eye Nearly half of the cerebral cortex is involved in processing visual information! Most of the eye is protected by a cushion of fat and the bony orbit

3. Copyright © 2010 Pearson Education, Inc. Figure 15.1a Eyelashes Sclera (covered by conjunctiva) Site where conjunctiva merges with cornea Lateral commissure Iris Medial commissure Lacrimal caruncle Eyelid Eyebrow Pupil Palpebral fissure (a) Surface anatomy of the right eye

4. Copyright © 2010 Pearson Education, Inc. Eyebrows Overlie the supraorbital margins Function in Shading the eye Preventing perspiration from reaching the eye

5. Copyright © 2010 Pearson Education, Inc. Eyelids Protect the eye anteriorly Palpebral fissure—slit separating eyelids Medial & Lateral Canthi – eye angles Caruncle—fleshy elevation at medial canthus; contains oil and sweat glands Tarsal plates—internal supporting C.T. sheet Levator palpebrae superioris—gives the upper eyelid mobility

6. Copyright © 2010 Pearson Education, Inc. Figure 15.1a Sclera (covered by conjunctiva) Site where conjunctiva merges with cornea Lateral commissure Medial commissure Lacrimal caruncle Eyelid Pupil Palpebral fissure (a) Surface anatomy of the right eye

7. Copyright © 2010 Pearson Education, Inc. Eyelids Eyelashes Nerve endings of follicles initiate reflex blinking Lubricating glands associated with the eyelids Tarsal glands-sebaceous glands that produce oily secretion to lubricate the eye

8. Copyright © 2010 Pearson Education, Inc. Conjunctiva Mucous membranes of the eye Palpebral conjunctiva: lines the eyelids Bulbar conjunctiva: covers the white of the eyes (anteriorly)

9. Copyright © 2010 Pearson Education, Inc. (b) Lateral view; some structures shown in sagittal section Levator palpebrae superioris muscle Orbicularis oculi muscle Tarsal plate Palpebral conjunctiva Tarsal glands Cornea Palpebral fissure Bulbar conjunctiva Orbicularis oculi muscle

10. Copyright © 2010 Pearson Education, Inc. Lacrimal Apparatus Consists of: Lacrimal gland and ducts that connect to nasal cavity Releases: dilute salt solution (tears) The solution also contains:mucus, antibodies, and lysozyme (bacteria destroying enzyme) Blinking spreads the tears towards the medial canthus, then into lacrimal puncta to lacrimal canaliculi then drain into nasolacrimal duct

11. Copyright © 2010 Pearson Education, Inc. Figure 15.2 Lacrimal gland Lacrimal punctum Lacrimal canaliculus Nasolacrimal duct Lacrimal sac

12. Copyright © 2010 Pearson Education, Inc. Extrinsic Eye Muscles The movement of the eye is controlled by six muscles on the external surface of each eye: Superior rectus: elevates eye Inferior rectus: depresses eye Lateral rectus: moves eye laterally Medial rectus: moves eye medially Inferior oblique: moves eye up and out Superior oblique: moves eye down and out

13. Copyright © 2010 Pearson Education, Inc. Figure 15.3a Inferior rectus muscle Inferior oblique muscle Superior oblique muscle Superior oblique tendon Superior rectus muscle Lateral rectus muscle (a) Lateral view of the right eye

14. Copyright © 2010 Pearson Education, Inc. Figure 15.3b Superior oblique muscle Common tendinous ring Trochlea Superior oblique tendon Superior rectus muscle (b) Superior view of the right eye Axis at center of eye Medial rectus muscle Inferior rectus muscle Lateral rectus muscle

15. Copyright © 2010 Pearson Education, Inc. The innervations to each muscle can be remembered by the following equation: (LR 6 SO 4 )O 3 Which means: Lateral rectus: controlled by CN # 6 (Abducens) Superior oblique: controlled by CN # 4 (Trochelar) All others: controlled by CN # 3 (oculomotor) Extrinsic Eye Muscles

16. Copyright © 2010 Pearson Education, Inc. Structure of the Eyeball Wall of eyeball contains three layers Fibrous Vascular Sensory

17. Copyright © 2010 Pearson Education, Inc. Lens Anterior segment (contains aqueous humor) Posterior segment (contains vitreous humor)

18. Copyright © 2010 Pearson Education, Inc. Fibrous Layer Outermost layer of dense avascular CT Two regions: sclera and cornea 1. Sclera: Opaque posterior region 2. Cornea: Transparent anterior part

19. Copyright © 2010 Pearson Education, Inc. Vascular Layer Middle layer Three regions: choroid, ciliary body, and iris 1.Choroid region Posterior portion Supplies blood to most of eyeball Brown pigment absorbs light to prevent its scattering

20. Copyright © 2010 Pearson Education, Inc. Vascular Layer 2.Ciliary body Ring of smooth muscle attached to and surrounding the lens Ciliary zonule (suspensory ligament): holds lens in position

21. Copyright © 2010 Pearson Education, Inc. Vascular Layer 3. Iris (smooth muscle) The anterior colored part of the eye Pupil: central opening of iris; the iris regulates the amount of light entering the eye Close vision and bright light- pupils constrict Distant and dim light- pupils dilate

22. Copyright © 2010 Pearson Education, Inc. Iris (two muscles) Sphincter pupillae Dilator pupillae Pupillary Sphincter muscle contraction decreases pupil size. Dilator muscle contraction increases pupil size.

23. Copyright © 2010 Pearson Education, Inc. Figure 15.4a Optic disc (blind spot) Optic nerve Choroid Sclera Ciliary body Ciliary zonule (suspensory ligament) Pupil Lens Iris

24. Copyright © 2010 Pearson Education, Inc. Sensory Layer (The Retina) Delicate two-layered membrane Pigmented layer -Outer layer that absorbs light and prevents its scattering Neural layer – contains photoreceptor cells (rods and cones), bipolar cells (connect photoreceptors to ganglion cells), and ganglion cells (axons form optic nerve)

25. Copyright © 2010 Pearson Education, Inc. Figure 15.6a (a) Posterior aspect of the eyeball Neural layer of retina Pigmented layer of retina Central artery and vein of retina Optic nerve Sclera Choroid Optic disc Pathway of light

26. Copyright © 2010 Pearson Education, Inc. Figure 15.6b Pigmented layer of retina Pathway of light Pathway of signal output (b) Cells of the neural layer of the retina Amacrine cell Horizontal cell Rod Photoreceptors Cone Bipolar cells Ganglion cells

27. Copyright © 2010 Pearson Education, Inc. Photoreceptors Rods More numerous at peripheral region of retina, away from the fovea centralis (area of retina containing only cones) Operate in dim light Provide indistinct, fuzzy, non color peripheral vision

28. Copyright © 2010 Pearson Education, Inc. Photoreceptors Cones Densest in center of retina and concentrated in an area called the fovea centralis (next to blind spot) Operate in bright light Provide high-acuity color vision

29. Copyright © 2010 Pearson Education, Inc. Photoreceptors Photoreceptor cells are distributed over entire retina except where the optic nerve leaves the eye called the blind spot

30. Copyright © 2010 Pearson Education, Inc. Cones There are three types of cones named for the colors of light absorbed: blue, green, and red Intermediate hues are perceived by activation of more than one type of cone at the same time Color blindness is due to a congenital lack of one or more of the cone types

31. Copyright © 2010 Pearson Education, Inc. Figure 15.7 Macula lutea Central artery and vein emerging from the optic disc Optic disc Retina

32. Copyright © 2010 Pearson Education, Inc. Internal Chambers and Fluids The lens and ciliary zonule separate the anterior and posterior segments Posterior segment contains vitreous humor that: A gel like substance which helps reinforce the eye internally

33. Copyright © 2010 Pearson Education, Inc. Figure 15.4a Optic disc (blind spot) Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera Ciliary body Ciliary zonule (suspensory ligament) Pupil Anterior segment (contains aqueous humor) Lens Posterior segment (contains vitreous humor)

34. Copyright © 2010 Pearson Education, Inc. Internal Chambers and Fluids Anterior segment is composed of two chambers Anterior chamber—between cornea and iris Posterior chamber—between iris and lens

35. Copyright © 2010 Pearson Education, Inc. Internal Chambers and Fluids Anterior segment contains aqueous humor Watery fluid continuously produced and drained Glaucoma: compression of the retina and optic nerve if drainage of aqueous humor is blocked

36. Copyright © 2010 Pearson Education, Inc. Figure 15.8 Scleral venous sinus Posterior chamber Anterior chamber Anterior segment (contains aqueous humor) Corneal- scleral junction Cornea Aqueous humor Iris Lens Posterior segment (contains vitreous humor) Ciliary zonule (suspensory ligament) Ciliary processes Ciliary muscle Ciliary body 1 2 3

37. Copyright © 2010 Pearson Education, Inc. Lens Biconvex, transparent, flexible,and avascular Allows precise focusing of light on the retina Cataracts (clouding of lens) occur as a consequence of aging, diabetes mellitus, heavy smoking, and frequent exposure to intense sunlight

38. Copyright © 2010 Pearson Education, Inc. Figure 15.9

39. Copyright © 2010 Pearson Education, Inc. Figure 15.4a Central artery and vein of the retina Optic disc (blind spot) Optic nerve Posterior pole Fovea centralis Macula lutea Retina Choroid Sclera Ora serrata (a) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. Ciliary body Ciliary zonule (suspensory ligament) Cornea Iris Anterior pole Pupil Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor)

40. Copyright © 2010 Pearson Education, Inc. Light Our eyes respond to visible light, (small portion of electromagnetic spectrum) Light: packets of energy = photons; travel in a wavelike fashion Rods and cones respond to different wavelengths of the visible spectrum

41. Copyright © 2010 Pearson Education, Inc. Figure 15.10 Wavelength (nm) Visible light (b) (a) Blue cones (420 nm) Rods (500 nm) Green cones (530 nm) Red cones (560 nm) X raysUVInfrared Micro- waves Radio waves Gamma rays Light absorption (pervent of maximum)

42. Copyright © 2010 Pearson Education, Inc. Refraction and Lenses Refraction Bending of a light ray when light passes from one transparent medium to another

43. Copyright © 2010 Pearson Education, Inc. Refraction and Lenses Light passing through a convex lens is: bent so that the rays converge at a focal point The image formed at the focal point is: upside-down and reversed right to left

44. Copyright © 2010 Pearson Education, Inc. Figure 15.12 Point sources (a) Focusing of two points of light. (b) The image is inverted—upside down and reversed. Focal points

45. Copyright © 2010 Pearson Education, Inc. Focusing Light on the Retina Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, neural layer of retina, photoreceptors Light is refracted At the cornea Entering the lens Leaving the lens Change in lens curvature allows for fine focusing of an image

46. Copyright © 2010 Pearson Education, Inc. Focusing for Distant Vision Light rays from distant objects are parallel and need little refraction Ciliary muscles are relaxed Lens is stretched flat by tension in the ciliary zonule

47. Copyright © 2010 Pearson Education, Inc. Figure 15.13a Lens Inverted image Ciliary zonule Ciliary muscle Nearly parallel rays from distant object (a) Lens is flattened for distant vision. Sympathetic input relaxes the ciliary muscle, tightening the ciliary zonule, and flattening the lens. Sympathetic activation

48. Copyright © 2010 Pearson Education, Inc. Focusing for Close Vision Light from a close object diverges as it approaches the eye; requires that the eye make three active adjustments

49. Copyright © 2010 Pearson Education, Inc. Focusing for Close Vision Close vision requires Accommodation—changing the lens shape by ciliary muscles to increase refractory power Presbyopia—loss of accommodation over age 50 Constriction—constriction of pupils to prevent the most divergent rays from entering eye Convergence—medial rotation of the eyeballs toward the object being viewed

50. Copyright © 2010 Pearson Education, Inc. Figure 15.13b Divergent rays from close object (b) Lens bulges for close vision. Parasympathetic input contracts the ciliary muscle, loosening the ciliary zonule, allowing the lens to bulge. Inverted image Parasympathetic activation

51. Copyright © 2010 Pearson Education, Inc. Problems of Refraction Myopia (nearsightedness)—focal point in front of retina Hyperopia (farsightedness)—focal point behind retina Astigmatism—caused by unequal curvatures in different parts of the cornea or lens

52. Copyright © 2010 Pearson Education, Inc. Figure 15.14 (1 of 3) Focal plane Focal point is on retina. Emmetropic eye (normal)

53. Copyright © 2010 Pearson Education, Inc. Figure 15.14 (2 of 3) Concave lens moves focal point further back. Eyeball too long Uncorrected Focal point is in front of retina. Corrected Myopic eye (nearsighted)

54. Copyright © 2010 Pearson Education, Inc. Figure 15.14 (3 of 3) Eyeball too short Uncorrected Focal point is behind retina. Corrected Convex lens moves focal point forward. Hyperopic eye (farsighted)

55. Copyright © 2010 Pearson Education, Inc. Functional Anatomy of Photoreceptors Rods and cones Outer segment of each contains visual pigments -molecules that change shape as they absorb light Inner segment of each joins the cell body

56. Copyright © 2010 Pearson Education, Inc. Figure 15.15a Process of bipolar cell Outer fiber Apical microvillus Discs containing visual pigments Melanin granules Discs being phagocytized Pigment cell nucleus Inner fibers Rod cell body Cone cell body Synaptic terminals Rod cell body Nuclei Mitochondria Connecting cilia Basal lamina (border with choroid) The outer segments of rods and cones are embedded in the pigmented layer of the retina. Pigmented layer Outer segment Inner segment

57. Copyright © 2010 Pearson Education, Inc. Figure 15.18 (1 of 2) 1 cGMP-gated channels open, allowing cation influx; the photoreceptor depolarizes. Voltage-gated Ca 2+ channels open in synaptic terminals. 2 Neurotransmitter is released continuously. 3 4 Hyperpolarization closes voltage-gated Ca 2+ channels, inhibiting neurotransmitter release. 5 No EPSPs occur in ganglion cell. 6 No action potentials occur along the optic nerve. 7 Neurotransmitter causes IPSPs in bipolar cell; hyperpolarization results. Na + Ca 2+ Photoreceptor cell (rod) Bipolar cell Ganglion cell In the dark

58. Copyright © 2010 Pearson Education, Inc. Figure 15.18 (2 of 2) 1 cGMP-gated channels are closed, so cation influx stops; the photoreceptor hyperpolarizes. Voltage-gated Ca 2+ channels close in synaptic terminals. 2 No neurotransmitter is released. 3 Lack of IPSPs in bipolar cell results in depolarization. 4 Depolarization opens voltage-gated Ca 2+ channels; neurotransmitter is released. 5 EPSPs occur in ganglion cell. 6 Action potentials propagate along the optic nerve. 7 Photoreceptor cell (rod) Bipolar cell Ganglion cell Light Ca 2+ In the light

59. Copyright © 2010 Pearson Education, Inc. Visual Pathway Medial fibers of the optic nerve cross at the optic chiasma then to optic tract Most fibers of the optic tracts continue to the thalamus From the thalamus to the primary visual cortex in the occipital lobe

60. Copyright © 2010 Pearson Education, Inc. Axons of ganglion cells form the Optic Nerve Optic chiasma optic tracts thalamus primary visual cortex in the occipital lobe of the brain conscious perception of the image Visual Pathway

61. Copyright © 2010 Pearson Education, Inc. Right eyeLeft eye Fixation point Optic tract Optic chiasma Optic nerve thalamus Occipital lobe (primary visual cortex)

62. Copyright © 2010 Pearson Education, Inc. HEARING AND BALANCE

63. Copyright © 2010 Pearson Education, Inc. The Ear: Hearing and Balance Three parts of the ear 1.External ear 2.Middle ear 3.Internal ear

64. Copyright © 2010 Pearson Education, Inc. The Ear: Hearing and Balance External ear and middle ear are involved with: hearing Internal ear (labyrinth) functions in both: hearing and equilibrium

65. Copyright © 2010 Pearson Education, Inc. Figure 15.25a External acoustic meatus Auricle (pinna) (a) The three regions of the ear Helix Lobule Pharyngotympanic (auditory) tube Tympanic membrane External ear Middle ear Internal ear (labyrinth)

66. Copyright © 2010 Pearson Education, Inc. External Ear The auricle (pinna) is composed of: Helix (rim) Lobule (earlobe) External acoustic meatus (auditory canal) Short, curved tube lined with skin bearing hairs, and ceruminous glands

67. Copyright © 2010 Pearson Education, Inc. Middle Ear Tympanic membrane (eardrum) Boundary between external and middle ear CT membrane that vibrates in response to sound Transfers sound energy to bones of middle ear

68. Copyright © 2010 Pearson Education, Inc. Middle Ear Pharyngotympanic tube—connects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure

69. Copyright © 2010 Pearson Education, Inc. Pharyngotympanic (auditory) tube Auditory ossicles Tympanic membrane Semicircular canals Cochlea Cochlear nerve Vestibular nerve Oval window (deep to stapes) Round window Incus Malleus Stapes (b) Middle and internal ear Vestibule

70. Copyright © 2010 Pearson Education, Inc. Ear Ossicles Three small bones in middle ear cavity: the malleus, incus, and stapes Transmit vibratory motion of the eardrum to the oval window Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to the hearing receptors

71. Copyright © 2010 Pearson Education, Inc. Figure 15.26 Pharyngotym- panic tube Tensor tympani muscle Tympanic membrane (medial view) Stapes Malleus View Superior Anterior Lateral Incus Epitympanic recess Stapedius muscle

72. Copyright © 2010 Pearson Education, Inc. Internal Ear Bony labyrinth Winding channels in the temporal bone Three parts: vestibule, semicircular canals, and cochlea Filled with perilymph Series of membranous sacs within the bony labyrinth Filled with endolymph

73. Copyright © 2010 Pearson Education, Inc. Figure 15.27 Anterior Semicircular ducts in semicircular canals Posterior Lateral Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule Stapes in oval window Temporal bone Facial nerve Vestibular nerve Superior vestibular ganglion Inferior vestibular ganglion Cochlear nerve Maculae Spiral organ (of Corti) Cochlear duct in cochlea Round window

74. Copyright © 2010 Pearson Education, Inc. Vestibule Central egg-shaped cavity of the bony labyrinth Contains two membranous sacs that: House equilibrium receptor regions called maculae Maculae respond to pull of gravity and changes in head position

75. Copyright © 2010 Pearson Education, Inc. Figure 15.35 Otolithic membrane Kinocilium Stereocilia Receptor potential Nerve impulses generated in vestibular fiber When hairs bend toward the kinocilium, the hair cell depolarizes, exciting the nerve fiber, which generates more frequent action potentials. When hairs bend away from the kinocilium, the hair cell hyperpolarizes, inhibiting the nerve fiber, and decreasing the action potential frequency. Depolarization Hyperpolarization

76. Copyright © 2010 Pearson Education, Inc. Semicircular Canals Three canals are oriented along all three planes (x,y,z) Membranous semicircular ducts line each canal Ampulla of each canal houses equilibrium receptor region called the crista ampullaris Receptors respond to rotational movements of the head

77. Copyright © 2010 Pearson Education, Inc. Hair cell Supporting cell Crista ampullaris Crista ampullaris Endolymph Cupula (a) Anatomy of a crista ampullaris in a semicircular canal (b) Scanning electron micrograph of a crista ampullaris (200x)

78. Copyright © 2010 Pearson Education, Inc. Equilibrium Impulses sent from the vestibule (maculae) or from ampulla (crista ampullaris) travel along the vestibular nerve which quickly merges with the cochlear nerve to form the vestibulocochlear nerve (CN #8)

79. Copyright © 2010 Pearson Education, Inc. Anterior Semicircular ducts in semicircular canals Posterior Lateral Cristae ampullares in the membranous ampullae Utricle in vestibule Saccule in vestibule Stapes in oval window Temporal bone Vestibular nerve Cochlear nerve Maculae Spiral organ (of Corti) Cochlear duct in cochlea Round window

80. Copyright © 2010 Pearson Education, Inc. The Cochlea A spiral, conical, bony chamber Extends from the vestibule Contains the cochlear duct, which houses the spiral organ (of Corti)

81. Copyright © 2010 Pearson Education, Inc. Organ of Corti Runs through center of cochlea Has hair cells(nerve cells) and supporting cells Tectorial membrane- gel-like mass that cilia of hair cells are embedded in Basilar membrane-fibrous “floor” of organ of corti Bending of the cilia: excites hair cells Sound and the Cochlea

82. Copyright © 2010 Pearson Education, Inc. Figure 15.28c (c) Tectorial membrane Inner hair cell Outer hair cells Hairs (stereocilia) Afferent nerve fibers Basilar membrane Fibers of cochlear nerve Supporting cells

83. Copyright © 2010 Pearson Education, Inc. Figure 15.31a Scala tympani Cochlear duct Basilar membrane 1 Sound waves vibrate the tympanic membrane. 2 Auditory ossicles vibrate. Pressure is amplified. 3 Pressure waves created by the stapes pushing on the oval window move through fluid in the scala vestibuli. Sounds with frequencies below hearing travel through the helicotrema and do not excite hair cells. Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane and deflecting hairs on inner hair cells. MalleusIncus Auditory ossicles Stapes Oval window Scala vestibuli Helicotrema Cochlear nerve 3 2 1 Round window Tympanic membrane (a) Route of sound waves through the ear

84. Copyright © 2010 Pearson Education, Inc. Transmission of Sound to the Internal Ear Transmission of Sound to the Inner Ear Sound waves enter the external acoustic canal and cause tympanic membrane to vibrate Ossicles vibrate and amplify the pressure at the oval window Pressure waves move through perilymph Sounds in the hearing range go through the cochlear duct, ultimately causing bending of hair cells Impulses from the cochlea pass: along the cochlear nerve, which then merges with the vestibular nerve (forming vestibulocochlear N.) that travels to the primary auditory cortex in temporal lobe of brain

85. Copyright © 2010 Pearson Education, Inc. Deafness Hearing loss can be temporary or permanent Common causes: Middle ear infections Conduction deafness Can be caused by: Impacted earwax Ruptured eardrum Middle ear inflammations Otosclerosis

86. Copyright © 2010 Pearson Education, Inc. Nerve Deafness Can be caused by: Gradual loss of hair cells throughout life Single explosive loud noise Prolonged exposure to loud noise Degeneration of cochlear nerve, tumors in auditory cortex, etc. Deafness

87. Copyright © 2010 Pearson Education, Inc. Tinnitus Ringing or clicking sound in ears in the absence of auditory stimuli One of the first symptoms of cochlear degeneration Can be caused by middle ear inflammation