1. © 2012 Pearson Education, Inc. PowerPoint ® Lecture Presentations prepared by Jason LaPres Lone Star College—North Harris 17 The Special Senses

2. © 2012 Pearson Education, Inc. An Introduction to the Special Senses Learning Outcomes 17-1 Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the brain, and explain the physiological basis of olfactory discrimination. 17-2 Describe the sensory organs of taste, trace the gustatory pathways to their destinations in the brain, and explain the physiological basis of gustatory discrimination. 17-3 Identify the internal and accessory structures of the eye, and explain the functions of each.

3. © 2012 Pearson Education, Inc. An Introduction to the Special Senses Learning Outcomes 17-4 Explain color and depth perception, describe how light stimulates the production of nerve impulses, and trace the visual pathways to their destinations in the brain. 17-5 Describe the structures of the external, middle, and internal ear, explain their roles in equilibrium and hearing, and trace the pathways for equilibrium and hearing to their destinations in the brain.

4. © 2012 Pearson Education, Inc. An Introduction to the Special Senses Five Special Senses 1.Olfaction 2.Gustation 3.Vision 4.Equilibrium 5.Hearing

5. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Olfactory Organs Provide sense of smell Located in nasal cavity on either side of nasal septum Made up of two layers 1.Olfactory epithelium 2. Lamina propria

6. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Layers of Olfactory Organs Olfactory epithelium contains: Olfactory receptors Supporting cells Basal (stem) cells

7. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Layers of Olfactory Organs Lamina propria contains: Areolar tissue Blood vessels Nerves Olfactory glands

8. © 2012 Pearson Education, Inc. Figure 17-1a The Olfactory Organs Olfactory epithelium Olfactory Pathway to the Cerebrum Olfactory nerve fibers (N I) Olfactory bulb Olfactory tract Central nervous system Superior nasal concha Cribriform plate The olfactory organ on the left side of the nasal septum

9. © 2012 Pearson Education, Inc. Figure 17-1b The Olfactory Organs Olfactory epithelium Cribriform plate Lamina propria Basal cell: divides to replace worn-out olfactory receptor cells Olfactory gland To olfactory bulb Olfactory nerve fibers Developing olfactory receptor cell Olfactory receptor cell Supporting cell Mucous layer Knob Olfactory cilia: surfaces contain receptor proteins (see Spotlight Fig. 17  3) Subsance being smelled An olfactory receptor is a modified neuron with multiple cilia extending from its free surface.

10. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Olfactory Glands Secretions coat surfaces of olfactory organs Olfactory Receptors Highly modified neurons Olfactory reception Involves detecting dissolved chemicals as they interact with odorant-binding proteins

11. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Olfactory Pathways Axons leaving olfactory epithelium Collect into 20 or more bundles Penetrate cribriform plate of ethmoid Reach olfactory bulbs of cerebrum where first synapse occurs

12. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Olfactory Pathways Axons leaving olfactory bulb: Travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system Arriving information reaches information centers without first synapsing in thalamus

13. © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) Olfactory Discrimination Can distinguish thousands of chemical stimuli CNS interprets smells by the pattern of receptor activity Olfactory Receptor Population Considerable turnover Number of olfactory receptors declines with age

14. © 2012 Pearson Education, Inc. Figure 17-2 Olfactory and Gustatory Receptors Olfaction and gustation are special senses that provide us with vital information about our environment. Although the sensory information provided is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons. Stimulus Dendrites Specialized olfactory neuron to CNS Stimulus removed Action potentials Stimulus Threshold Generator potential

15. © 2012 Pearson Education, Inc. Figure 17-2 Olfactory and Gustatory Receptors The binding of an odorant to its receptor protein leads to the activation of adenylyl cyclase, the enzyme that converts ATP to cyclic-AMP (cAMP). The cAMP then opens sodium channels in the plasma membrane, which, as a result, begins to depolarize. If sufficient depolarization occurs, an action potential is triggered in the axon, and the information is relayed to the CNS. In general, odorants are small organic molecules. The strongest smells are associated with molecules of either high water or high lipid solubilities. As few as four odorant molecules can activate an olfactory receptor. Olfactory reception occurs on the surface membranes of the olfactory cilia. Odorants  dissolved chemicals that stimulate olfactory receptors  interact with receptors called odorant- binding proteins on the membrane surface. Depolarized membrane Sodium ions enter Closed sodium channel RECEPTOR CELL MUCOUS LAYER Odorant molecule Active enzyme Inactive enzyme

16. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Gustation Provides information about the foods and liquids consumed Taste Receptors (Gustatory Receptors) Are distributed on tongue and portions of pharynx and larynx Clustered into taste buds

17. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Taste Buds Associated with epithelial projections (lingual papillae) on superior surface of tongue

18. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Three Types of Lingual Papillae 1.Filiform papillae Provide friction Do not contain taste buds 2.Fungiform papillae Contain five taste buds each 3.Circumvallate papillae Contain 100 taste buds each

19. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Taste Buds Contain: Basal cells Gustatory cells Extend taste hairs through taste pore Survive only 10 days before replacement Monitored by cranial nerves that synapse within solitary nucleus of medulla oblongata Then on to thalamus and primary sensory cortex

20. © 2012 Pearson Education, Inc. Figure 17-3a Gustatory Receptors Water receptors (pharynx) Umami Sour Bitter Salty Sweet Landmarks and receptors on the tongue

21. © 2012 Pearson Education, Inc. Figure 17-3b Gustatory Receptors Taste buds Circumvallate papilla Fungiform papilla Filiform papillae The structure and representative locations of the three types of lingual papillae. Taste receptors are located in taste buds, which form pockets in the epithelium of fungiform or circumvillate papillae.

22. © 2012 Pearson Education, Inc. Figure 17-3c Gustatory Receptors Taste buds Nucleus of transitional cell Nucleus of gustatory cell Nucleus of basal cell Taste bud LM  650 LM  280 Transitional cell Gustatory cell Basal cell Taste hairs (microvilli) Taste pore Taste buds in a circumvallate papilla. A diagrammatic view of a taste bud, showing gustatory (receptor) cells and supporting cells.

23. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Gustatory Discrimination Four primary taste sensations 1.Sweet 2.Salty 3.Sour 4.Bitter

24. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Additional Human Taste Sensations Umami Characteristic of beef/chicken broths and Parmesan cheese Receptors sensitive to amino acids, small peptides, and nucleotides Water Detected by water receptors in the pharynx

25. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Gustatory Discrimination Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors Chemically gated ion channels Stimulation produces depolarization of cell Sweet, bitter, and umami stimuli G proteins Gustducins

26. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) End Result of Taste Receptor Stimulation Release of neurotransmitters by receptor cell Dendrites of sensory afferents wrapped by receptor membrane Neurotransmitters generate action potentials in afferent fiber

27. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) Taste Sensitivity Exhibits significant individual differences Some conditions are inherited For example, phenylthiocarbamide (PTC) 70% of Caucasians taste it but 30% do not Number of taste buds Begins declining rapidly by age 50

28. © 2012 Pearson Education, Inc. Figure 17-2 Olfactory and Gustatory Receptors Receptor cell Stimulus removed Stimulus Threshold Receptor depolarization Stimulus Receptor cell Synapse Axon of sensory neuron Stimulus Axon Action potentials Generator potential Synaptic delay to CNS

29. © 2012 Pearson Education, Inc. Figure 17-2 Olfactory and Gustatory Receptors Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell. Salt and Sour Receptors Receptors responding to stimuli that produce sweet, bitter, and umami sensations are linked to G proteins called gustducins (GUST-doos- inz)  protein complexes that use second messengers to produce their effects. Sweet, Bitter, and Umami Receptors Sour, salt Gated ion channel Resting plasma membrane Channel opens Depolarized membrane Sweet, bitter, or umami Membrane receptor Active G protein Inactive G protein Active G protein Inactive 2nd messenger Active 2nd messenger Depolarization of membrane stimulates release of chemical neurotransmitters. Activation of second messengers stimulates release of chemical neurotransmitters.

30. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Accessory Structures of the Eye Provide protection, lubrication, and support Include: The palpebrae (eyelids) The superficial epithelium of eye The lacrimal apparatus

31. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Continuation of skin Blinking keeps surface of eye lubricated, free of dust and debris Palpebral fissure Gap that separates free margins of upper and lower eyelids

32. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Medial canthus and lateral canthus Where two eyelids are connected Eyelashes Robust hairs that prevent foreign matter from reaching surface of eye

33. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Tarsal glands Secrete lipid-rich product that helps keep eyelids from sticking together

34. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Superficial Epithelium of Eye Lacrimal caruncle Mass of soft tissue Contains glands producing thick secretions Contributes to gritty deposits that appear after good night’s sleep Conjunctiva Epithelium covering inner surfaces of eyelids (palpebral conjunctiva) and outer surface of eye (ocular conjunctiva)

35. © 2012 Pearson Education, Inc. Figure 17-4a External Features and Accessory Structures of the Eye Gross and superficial anatomy of the accessory structures Sclera Lateral canthus Eyelashes Pupil Palpebra Palpebral fissure Medial canthus Lacrimal caruncle Corneal limbus

36. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Lacrimal Apparatus Produces, distributes, and removes tears Fornix Pocket where palpebral conjunctiva joins ocular conjunctiva Lacrimal gland (tear gland) Secretions contain lysozyme, an antibacterial enzyme

37. © 2012 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Tears Collect in the lacrimal lake Pass through: Lacrimal puncta Lacrimal canaliculi Lacrimal sac Nasolacrimal duct To reach inferior meatus of nose

38. © 2012 Pearson Education, Inc. Figure 17-4b External Features and Accessory Structures of the Eye Lacrimal gland ducts Lacrimal gland Ocular conjunctiva Lateral canthus Lower eyelid Orbital fat Inferior rectus muscle Inferior oblique muscle Superior rectus muscle Tendon of superior oblique muscle Lacrimal punctum Lacrimal caruncle Superior lacrimal canaliculus Medial canthus Inferior lacrimal canaliculus Lacrimal sac Nasolacrimal duct Opening of nasolacrimal duct Inferior nasal concha The organization of the lacrimal apparatus.

39. © 2012 Pearson Education, Inc. 17-3 The Eye Three Layers of the Eye 1.Outer fibrous layer 2.Intermediate vascular layer 3.Deep inner layer

40. © 2012 Pearson Education, Inc. 17-3 The Eye Eyeball Is hollow Is divided into two cavities 1.Large posterior cavity 2.Smaller anterior cavity

41. © 2012 Pearson Education, Inc. Figure 17-5a The Sectional Anatomy of the Eye Optic nerve Fovea Retina Choroid Sclera Sagittal section of left eye Lens Fornix Palpebral conjunctiva Eyelash Ocular conjunctiva Cornea Pupil Iris Limbus Ora serrata

42. © 2012 Pearson Education, Inc. Figure 17-5b The Sectional Anatomy of the Eye Cornea Sclera Neural part Pigmented part Fibrous layer Neural layer (retina) Anterior cavity Posterior cavity Vascular layer (uvea) Iris Ciliary body Choroid Horizontal section of right eye

43. © 2012 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye Lacrimal punctum Nose Lens Edge of pupil Visual axis Anterior cavity Posterior chamber Anterior chamber Lacrimal caruncle Medial canthus Ciliary processes Ciliary body Ora serrata Ethmoidal labyrinth Medial rectus muscle Optic disc Optic nerve Central artery and vein Horizontal dissection of right eye Orbital fat Fovea Lateral rectus muscle Posterior cavity Retina Choroid Sclera Lateral canthus Lower eyelid Conjunctiva Corneal limbus Suspensory ligament of lens Iris Cornea

44. © 2012 Pearson Education, Inc. 17-3 The Eye The Fibrous Layer Sclera (white of the eye) Cornea Corneal limbus (border between cornea and sclera)

45. © 2012 Pearson Education, Inc. 17-3 The Eye Vascular Layer (Uvea) Functions 1.Provides route for blood vessels and lymphatics that supply tissues of eye 2.Regulates amount of light entering eye 3.Secretes and reabsorbs aqueous humor that circulates within chambers of eye 4.Controls shape of lens, which is essential to focusing

46. © 2012 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye Lacrimal punctum Nose Lens Edge of pupil Visual axis Anterior cavity Posterior chamber Anterior chamber Lacrimal caruncle Medial canthus Ciliary processes Ciliary body Ora serrata Ethmoidal labyrinth Medial rectus muscle Optic disc Optic nerve Central artery and vein Horizontal dissection of right eye Orbital fat Fovea Lateral rectus muscle Posterior cavity Retina Choroid Sclera Lateral canthus Lower eyelid Conjunctiva Corneal limbus Suspensory ligament of lens Iris Cornea

47. © 2012 Pearson Education, Inc. 17-3 The Eye The Vascular Layer Iris Contains papillary muscles Change diameter of pupil

48. © 2012 Pearson Education, Inc. Figure 17-6 The Pupillary Muscles Pupillary constrictor (sphincter) Pupil The pupillary dilator muscles extend radially away from the edge of the pupil. Contraction of these muscles enlarges the pupil. Pupillary dilator (radial) Decreased light intensity Increased sympathetic stimulation Increased light intensity Increased parasympathetic stimulation The pupillary constrictor muscles form a series of concentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases.

49. © 2012 Pearson Education, Inc. 17-3 The Eye The Vascular Layer Ciliary Body Extends posteriorly to level of ora serrata Serrated anterior edge of thick, inner portion of neural tunic Contains ciliary processes, and ciliary muscle that attaches to suspensory ligaments of lens

50. © 2012 Pearson Education, Inc. 17-3 The Eye The Vascular Layer The choroid Vascular layer that separates fibrous and inner layers posterior to ora serrata Delivers oxygen and nutrients to retina

51. © 2012 Pearson Education, Inc. 17-3 The Eye The Inner Layer Outer layer called pigmented part Inner called neural part (retina) Contains visual receptors and associated neurons Rods and cones are types of photoreceptors Rods Do not discriminate light colors Highly sensitive to light Cones Provide color vision Densely clustered in fovea, at center of macula

52. © 2012 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye Lacrimal punctum Nose Lens Edge of pupil Visual axis Anterior cavity Posterior chamber Anterior chamber Lacrimal caruncle Medial canthus Ciliary processes Ciliary body Ora serrata Ethmoidal labyrinth Medial rectus muscle Optic disc Optic nerve Central artery and vein Horizontal dissection of right eye Orbital fat Fovea Lateral rectus muscle Posterior cavity Retina Choroid Sclera Lateral canthus Lower eyelid Conjunctiva Corneal limbus Suspensory ligament of lens Iris Cornea

53. © 2012 Pearson Education, Inc. Figure 17-7a The Organization of the Retina Amacrine cell Horizontal cellCone Rod Pigmented part of retina Rods and cones Bipolar cells Ganglion cells LIGHT The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber).

54. © 2012 Pearson Education, Inc. Figure 17-7a The Organization of the Retina Choroid Pigmented part of retina Rods and cones Bipolar cells Ganglion cells The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). Retina Nuclei of ganglion cells Nuclei of rods and cones Nuclei of bipolar cells LM  350

55. © 2012 Pearson Education, Inc. Figure 17-7b The Organization of the Retina Central retinal vein Central retinal artery Sclera Choroid Optic nerve Optic disc The optic disc in diagrammatic sagittal section. Pigmented part of retina Neural part of retina

56. © 2012 Pearson Education, Inc. Figure 17-7c The Organization of the Retina Fovea Macula A photograph of the retina as seen through the pupil. Central retinal artery and vein emerging from center of optic disc Optic disc (blind spot)

57. © 2012 Pearson Education, Inc. 17-3 The Eye Inner Neural Part Bipolar cells Neurons of rods and cones synapse with ganglion cells Horizontal cells Extend across outer portion of retina Amacrine cells Comparable to horizontal cell layer Where bipolar cells synapse with ganglion cells

58. © 2012 Pearson Education, Inc. 17-3 The Eye Horizontal and Amacrine Cells Facilitate or inhibit communication between photoreceptors and ganglion cells Alter sensitivity of retina Optic Disc Circular region just medial to fovea Origin of optic nerve Blind spot

59. © 2012 Pearson Education, Inc. Figure 17-8 A Demonstration of the Presence of a Blind Spot

60. © 2012 Pearson Education, Inc. 17-3 The Eye The Chambers of the Eye Ciliary body and lens divide eye into: Large posterior cavity (vitreous chamber) Smaller anterior cavity Anterior chamber Extends from cornea to iris Posterior chamber Between iris, ciliary body, and lens

61. © 2012 Pearson Education, Inc. 17-3 The Eye Aqueous Humor Fluid circulates within eye Diffuses through walls of anterior chamber into scleral venous sinus (canal of Schlemm) Re-enters circulation Intraocular Pressure Fluid pressure in aqueous humor Helps retain eye shape

62. © 2012 Pearson Education, Inc. Figure 17-9 The Circulation of Aqueous Humor Cornea Pupil Lens Scleral venous sinus Body of iris Conjunctiva Ciliary body Sclera Choroid Retina Posterior cavity (vitreous chamber) Anterior cavity Anterior chamber Posterior chamber Ciliary process Suspensory ligaments Pigmented epithelium

63. © 2012 Pearson Education, Inc. 17-3 The Eye Large Posterior Cavity (Vitreous Chamber) Vitreous body Gelatinous mass Helps stabilize eye shape and supports retina

64. © 2012 Pearson Education, Inc. 17-3 The Eye The Lens Lens fibers Cells in interior of lens No nuclei or organelles Filled with crystallins, which provide clarity and focusing power to lens Cataract Condition in which lens has lost its transparency

65. © 2012 Pearson Education, Inc. 17-3 The Eye Light Refraction Bending of light by cornea and lens Focal point Specific point of intersection on retina Focal distance Distance between center of lens and focal point

66. © 2012 Pearson Education, Inc. Figure 17-10 Factors Affecting Focal Distance Focal distance Light from distant source (object) Close source The closer the light source, the longer the focal distance Focal distance Focal point Lens The rounder the lens, the shorter the focal distance Focal distance

67. © 2012 Pearson Education, Inc. 17-3 The Eye Light Refraction of Lens Accommodation Shape of lens changes to focus image on retina Astigmatism Condition where light passing through cornea and lens is not refracted properly Visual image is distorted

68. © 2012 Pearson Education, Inc. Figure 17-11 Accommodation For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Ciliary muscle contracted Focal point on fovea Lens flattened Ciliary muscle relaxed For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened

69. © 2012 Pearson Education, Inc. Figure 17-11a Accommodation For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Ciliary muscle contracted Focal point on fovea

70. © 2012 Pearson Education, Inc. Figure 17-11b Accommodation Lens flattened Ciliary muscle relaxed For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened

71. © 2012 Pearson Education, Inc. 17-3 The Eye Light Refraction of Lens Image reversal Visual acuity Clarity of vision “Normal” rating is 20/20

72. © 2012 Pearson Education, Inc. Figure 17-12a Image Formation Light from a point at the top of an object is focused on the lower retinal surface.

73. © 2012 Pearson Education, Inc. Figure 17-12b Image Formation Light from a point at the bottom of an object is focused on the upper retinal surface.

74. © 2012 Pearson Education, Inc. Figure 17-12c Image Formation Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.)

75. © 2012 Pearson Education, Inc. Figure 17-12d Image Formation Light rays projected from a horizontal object show why the image arrives with a left and right reversal. The image also arrives upside down. (As noted in the text, these representa- tions are not drawn to scale.)

76. © 2012 Pearson Education, Inc. Figure 17-13 Accommodation Problems The eye has a fixed focal length and focuses by varying the shape of the lens. A camera lens has a fixed size and shape and focuses by varying the distance to the film.

77. © 2012 Pearson Education, Inc. Figure 17-13 Accommodation Problems Emmetropia (normal vision)

78. © 2012 Pearson Education, Inc. Figure 17-13 Accommodation Problems Diverging lens Myopia corrected with a diverging, concave lens If the eyeball is too deep or the resting curvature of the lens is too great, the image of a distant object is projected in front of the retina. The person will see distant objects as blurry and out of focus. Vision at close range will be normal because the lens is able to round as needed to focus the image on the retina. Myopia (nearsightedness)

79. © 2012 Pearson Education, Inc. Figure 17-13 Accommodation Problems Hyperopia (farsightedness) If the eyeball is too shallow or the lens is too flat, hyperopia results. The ciliary muscle must contract to focus even a distant object o the retina. And at close range the lens cannot provide enough refraction to focus an image on the retina. Older people become farsighted as their lenses lose elasticity, a form of hyperopia called presbyopia (presbys, old man). Hyperopia corrected with a converging, convex lens Converging lens

80. © 2012 Pearson Education, Inc. Figure 17-13 Accommodation Problems Surgical Correction Variable success at correcting myopia and hyperopia has been achieved by surgery that reshapes the cornea. In Photorefractive keratectomy (PRK) a computer-guided laser shapes the cornea to exact specifications. The entire procedure can be done in less than a minute. A variation on PRK is called LASIK (Laser-Assisted in-Situ Keratomileusis). In this procedure the interior layers of the cornea are reshaped and then re-covered by the flap of original outer corneal epithelium. Roughly 70 percent of LASIK patients achieve normal vision, and LASIK has become the most common form of refractive surgery. Even after surgery, many patients still need reading glasses, and both immediate and long-term visual problems can occur.

81. © 2012 Pearson Education, Inc. 17-4 Visual Physiology Visual Physiology Rods Respond to almost any photon, regardless of energy content Cones Have characteristic ranges of sensitivity

82. © 2012 Pearson Education, Inc. 17-4 Visual Physiology Anatomy of Rods and Cones Outer segment with membranous discs Inner segment Narrow stalk connects outer segment to inner segment

83. © 2012 Pearson Education, Inc. 17-4 Visual Physiology Anatomy of Rods and Cones Visual pigments Is where light absorption occurs Derivatives of rhodopsin (opsin plus retinal) Retinal synthesized from vitamin A

84. © 2012 Pearson Education, Inc. Figure 17-14a Structure of Rods, Cones, and Rhodopsin Molecule Pigment Epithelium Melanin granules Outer Segment Inner Segment Discs Connecting stalks Mitochondria Golgi apparatus Nuclei Cone Rods In a cone, the discs are infoldings of the plasma membrane, and the outer segment tapers to a blunt point. In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Each photoreceptor synapses with a bipolar cell. Bipolar cell Structure of rods and cones. LIGHT

85. © 2012 Pearson Education, Inc. Figure 17-14b Structure of Rods, Cones, and Rhodopsin Molecule In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Rhodopsin molecule Opsin Retinal Structure of rhodospin molecule.

86. © 2012 Pearson Education, Inc. 17-4 Visual Physiology Color Vision Integration of information from red, green, and blue cones Color blindness Inability to detect certain colors

87. © 2012 Pearson Education, Inc. Figure 17-15 Cone Types and Sensitivity to Color Rods Blue cones Green cones Red cones VioletBlueGreenYellowOrangeRed W A V E L E N G T H (nm) Light absorption (percent of maximum)

88. © 2012 Pearson Education, Inc. Figure 17-16 A Standard Test for Color Vision

89. © 2012 Pearson Education, Inc. 17-4 Visual Physiology Photoreception Photon strikes retinal portion of rhodopsin molecule embedded in membrane of disc Opsin is activated Bound retinal molecule has two possible configurations 11-cis form 11-trans form

90. © 2012 Pearson Education, Inc. Figure 17-17 Photoreception Opsin activation occurs The bound retinal molecule has two possible configurations: the 11-cis form and the 11-trans form. Normally, the molecule is in the 11-cis form; on absorbing light it changes to the more linear 11-trans form. This change activates the opsin molecule. Photon Rhodopsin 11-trans retinal 11-cis retinal Opsin

91. © 2012 Pearson Education, Inc. Figure 17-17 Photoreception PDE Disc membrane Transducin Opsin activates transducin, which in turn activates phosphodiestease (PDE) Transducin is a G protein  a membrane-bound enzyme complex In this case, transducin is activated by opsin, and transducin in turn activates phosphodiesterase (PDE).

92. © 2012 Pearson Education, Inc. Figure 17-17 Photoreception Cyclic-GMP levels decline and gated sodium channels close Phosphodiesterase is an enzyme that breaks down cGMP. The removal of cGMP from the gated sodium channels results in their inactivation. The rate of Na  entry into the cytoplasm is then decreased. GMP cGMP

93. © 2012 Pearson Education, Inc. Figure 17-17 Photoreception Dark current is reduced and rate of neurotransmitter release declines ACTIVE STATE IN LIGHT

94. © 2012 Pearson Education, Inc. 17-4 Visual Physiology Recovery after Stimulation Bleaching Rhodopsin molecule breaks down into retinal and opsin Night blindness Results from deficiency of vitamin A

95. © 2012 Pearson Education, Inc. Figure 17-18 Bleaching and Regeneration of Visual Pigments On absorbing light, retinal changes to a more linear shape. This change activates the opsin molecule. Opsin activation changes the Na  permeability of the outer segment, and this changes the rate of neurotransmitter release by the inner segment at its synapse with a bipolar cell. Na  11-trans retinal Neuro- transmitter release Bipolar cell Changes in bipolar cell activity are detected by one or more ganglion cells. The location of the stimulated ganglion cell indicates the specific portion of the retina stimulated by the arriving photons. Ganglion cell Opsin 11-trans retinal ADP ATP enzyme 11-cis retinal Photon Opsin 11-cis retinal and opsin are reassembled to form rhodopsin. After absorbing a photon, the rhodopsin molecule begins to break down into retinal and opsin, a process known as bleaching. The retinal is converted to its original shape. This conversion requires energy in the form of ATP. Once the retinal has been converted, it can recombine with opsin. The rhodopsin molecule is now ready to repeat the cycle. The regeneration process takes time; after exposure to very bright light, photoreceptors are inactivated while pigment regeneration is under way.