The Special Senses. Lecture Presentation by Lori Garrett Pearson Education, Inc.

Transcription

1 15 The Special Senses Lecture Presentation by Lori Garrett

2 Note to the Instructor: For the third edition of Visual Anatomy & Physiology, we have updated our PowerPoints to fully integrate text and art. The pedagogy now more closely matches that of the textbook. The goal of this revised formatting is to help your students learn from the art more effectively. However, you will notice that the labels on the embedded PowerPoint art are not editable. You can easily import editable art by doing the following: Copying slides from one slide set into another You can easily copy the Label Edit art into the Lecture Presentations by using either the PowerPoint Slide Finder dialog box or Slide Sorter view. Using the Slide Finder dialog box allows you to explicitly retain the source formatting of the slides you insert. Using the Slide Finder dialog box in PowerPoint: 1. Open the original slide set in PowerPoint. 2. On the Slides tab in Normal view, click the slide thumbnail that you want the copied slides to follow. 3. On the toolbar at the top of the window, click the drop down arrow on the New Slide tab. Select Reuse Slides. 4. Click Browse to look for the file; in the Browse dialog box, select the file, and then click Open. 5. If you want the new slides to keep their current formatting, in the Slide Finder dialog box, select the Keep source formatting checkbox. When this checkbox is cleared, the copied slides assume the formatting of the slide they are inserted after. 6. To insert selected slides: Click the slides you want to insert. Slides will place immediately after the slide you have selected in the Slides tab in Normal view.

3 Section 1: Olfaction and Gustation Learning Outcomes 15.1 Explain the roles of generator potentials and depolarization in sensory neurons and receptor cells Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the cerebrum, and explain how olfactory perception occurs Describe the sensory organs of gustation Describe gustatory reception, briefly describe the physiological processes involved in taste, and trace the gustatory pathway.

4 Module 15.1: A generator potential is a depolarization of the membrane Five special senses 1. Olfaction (smell) 2. Gustation (taste) 3. Vision 4. Equilibrium (balance) 5. Hearing All originate with one of two types of sensory receptor cells 1. Dendrites of specialized neurons Example: olfactory receptors 2. Specialized cells that synapse with sensory neurons Depolarization of sensory neuron = a generator potential

5 Module 15.1: Generator potential 1. Olfactory receptors are dendrites of specialized neurons Dissolved odorants bind to olfactory receptors Triggers depolarization = generator potential With strong enough stimulus, generator potential triggers action potentials that go to CNS

6 Module 15.1: Generator potential 2. Receptors for taste, vision, equilibrium, hearing are specialized cells with inexcitable membranes Synapse with sensory neurons Stimulation triggers graded depolarization

7 Module 15.1: Generator potential Graded depolarization of the receptor cell triggers neurotransmitter release Neurotransmitter depolarizes sensory neurons, causing generator potential that can trigger action potential Action potentials are propagated to CNS

8 Module 15.1: Review A. Where do the special senses originate? B. What is a generator potential? C. Compare olfactory receptors with receptors for the other special senses. Learning Outcome: Explain the roles of generator potentials and depolarization in sensory neurons and receptor cells.

9 Module 15.2: Olfaction involves specialized chemoreceptive neurons and delivers sensations directly to the cerebrum Olfaction = sense of smell Paired olfactory organs in nasal cavity, each side of nasal septum Contain olfactory receptor cells Distributed along cribriform plate, superior portion of the perpendicular plate, superior nasal conchae Olfactory organs have two layers 1. Olfactory epithelium 2. Lamina propria

10 Module 15.2: Olfaction Olfactory epithelium Olfactory receptor cells (modified neurons) Each forms knob with up to 20 cilia-shaped dendrites projecting past epithelial surface into mucus million receptors in a 5-cm 2 area Supporting cells Basal cells (stem cells) constantly produce new receptor cells One of the few examples of neuronal replacement

11 Module 15.2: Olfaction Lamina propria Areolar tissue, blood vessels, nerves Olfactory glands secretions absorb water; form thick, pigmented mucus

12 An olfactory organ, showing the olfactory epithelium and lamina propria

13 Module 15.2: Olfaction Odorants = dissolved chemicals that stimulate olfactory neurons Bind membrane receptors (odorant-binding proteins) on dendrites of olfactory receptor cells Generally small organic molecules As few as four odorant molecules can activate receptor cell

14 Module 15.2: Olfaction Olfactory reception process 1. Odorant binds to receptor protein; activates adenylate cyclase (enzyme that converts ATP to cyclic AMP) 2. camp opens sodium channels in plasma membrane; starts depolarization 3. If enough depolarization occurs, action potential is triggered, and information is relayed to CNS

15 The process of olfaction

16 The process of olfaction

17 The process of olfaction

18 Module 15.2: Olfaction Olfactory pathway to the cerebrum 1. Chemicals in air bind odorant-binding proteins on olfactory cell membranes; stimulate sensory neurons in olfactory organ 2. Axons leave olfactory epithelium in bundles passing through cribriform plate (ethmoid) 3. First synapse occurs in olfactory bulb immediately superior to cribriform plate 4. Axons leaving olfactory bulb travel through olfactory tract to olfactory cortex, hypothalamus, and limbic system Distribution to limbic system (emotions) and hypothalamus (ANS) explains why smells can produce profound emotional and behavioral responses

19 The olfactory pathway

20 The olfactory pathway

21 The olfactory pathway

22 The olfactory pathway

23 The olfactory pathway

24 Module 15.2: Review A. Describe olfaction. B. Trace the olfactory pathway, beginning at the olfactory epithelium. C. Describe the events leading up to the depolarization and generation of an action potential by an olfactory receptor cell. Learning Outcome: Describe the sensory organs of smell, trace the olfactory pathways to their destinations in the cerebrum, and explain how olfactory perception occurs.

25 Module 15.3: Gustation involves epithelial chemoreceptor cells located in taste buds Gustation = taste Taste receptors (gustatory receptor cells) Most important receptors on superior surface of tongue Also in adjacent parts of pharynx, larynx, epiglottis Numbers decrease with age

26 Module 15.3: Gustation involves epithelial chemoreceptor cells located in taste buds Gustation = taste (continued) Lingual papillae = epithelial projections on tongue surface Contain taste buds = sensory structures with taste receptors that respond to various chemical stimuli, and specialized epithelial cells. Four types of lingual papillae: vallate papillae, foliate papillae, fungiform papillae, and filiform papillae

27 Module 15.3: Gustation Gustation = taste (continued) Vallate (vallum, wall) papillae Relatively large each contains up to 100 taste buds Surrounded by deep epithelial folds Form V at back of tongue

28 Module 15.3: Gustation Gustation = taste (continued) Foliate papillae lateral margins of posterior region of tongue Fungiform (fungus, mushroom) papillae about five taste buds each

29 Module 15.3: Gustation Gustation = taste (continued) Filiform (filum, thread) papillae provide friction to help tongue move objects around mouth Anterior two-third of superior surface of tongue NO taste buds

30 Module 15.3: Gustation

31 Module 15.3: Gustation Four primary taste sensations: sweet, salty, sour, bitter No difference in taste bud structure Taste buds in all portions of tongue provide all four sensations Umami = pleasant, savory taste characteristic of broths, cheese Binds receptors for amino acids, small peptides, nucleotides

32 Module 15.3: Gustation Four primary taste sensations: sweet, salty, sour, bitter (continued) Water receptors Concentrated in pharynx Output goes to hypothalamus; affects water balance and regulation of blood volume Prevent overingesting H 2 O

33 Module 15.3: Gustation Taste buds Recessed into epithelium Gustatory receptor cell (taste receptor cell) Extends slender microvilli (taste hairs) into surrounding fluids through a taste pore Typically lives about 10 days before it is replaced About gustatory cells in each taste bud Basal cells = stem cells that divide and mature to produce transitional cells that mature into new gustatory cells

34 Module 15.3: Gustation

35 Module 15.3: Gustation Taste receptor sensitivity Threshold varies for the four primary sensations More sensitive to unpleasant stimuli 100,000 times more sensitive to bitter; 1000 times more sensitive to sour (acids) than to sweet or salty Survival value acids burn tissues; many toxins are bitter Overall sensitivity declines with age leads to changing taste sensations with age

36 Module 15.3: Review A. Define gustation. B. Describe filiform papillae. C. Which taste receptors offer a survival advantage when tasting something for the first time? Learning Outcome: Describe the sensory organs of gustation.

37 Module 15.4: Gustatory reception relies on membrane receptors and ion channels, and sensations are carried by facial, glossopharyngeal, and vagus nerves Gustatory reception stimulated by dissolved chemicals (like smell) Chemicals contacting taste hairs may: Diffuse through plasma membrane leak channels Bind to receptor proteins of gustatory receptor cell ~ 90 percent of gustatory receptor cells respond to at least two taste stimuli Different tastes involve different receptor mechanisms

38 Module 15.4: Gustatory reception Two types of gustatory reception 1. Salt and sour receptors Sodium ions (salt) or hydrogen ions (sour) diffuse through Na + leak channels Membrane/cell depolarizes; neurotransmitter is released Neurotransmitters are released at synapse with sensory neurons Depolarization of sensory neurons leads to generator potential, which can produce action potentials along gustatory pathway to CNS

39 Module 15.4: Gustatory reception 2. Sweet, bitter, and umami receptors: Binding to these receptors activates G-protein complexes called gustducins (protein complexes that use second messengers to produce effects) Activated second messenger causes neurotransmitter release Neurotransmitters are released at synapse with sensory neurons Depolarization of sensory neurons leads to generator potential, which can produce action potentials along gustatory pathway to CNS

40 Different tastes involve different receptor mechanisms

41 Module 15.4: Gustatory reception Gustatory pathway gustatory receptor cells to cerebral cortex 1. Gustatory receptor cells respond to stimulation 2. Information is relayed on cranial nerves VII, IX, and X 3. Sensory afferents synapse in solitary nucleus of medulla oblongata 4. Postsynaptic neurons cross over; enter medial lemniscus of medulla oblongata 5. Synapse in thalamus, then go to gustatory cortex in insula for conscious perception

42 Module 15.4: Gustatory reception Gustatory pathway (continued) 1. Gustatory receptor cells bind dissolved chemicals Generator potential occurs Triggers action potentials

43 Module 15.4: Gustatory reception Gustatory pathway (continued) 2. Information is relayed on cranial nerves Facial nerve (VII) taste buds on anterior twothirds of tongue, from the tip to the vallate papillae Glossopharyngeal nerve (IX) vallate papillae, posterior one-third of tongue Vagus nerve (X) epiglottis

44 Module 15.4: Gustatory reception Gustatory pathway (continued) 3. Sensory afferents synapse in solitary nucleus of medulla oblongata

45 Module 15.4: Gustatory reception Gustatory pathway (continued) 4. Axons of postsynaptic neurons cross over; enter medial lemniscus of medulla oblongata

46 Module 15.4: Gustatory reception Gustatory pathway (continued) 5. Synapse in thalamus; then information is projected to appropriate portions of gustatory cortex of the insula

47 Module 15.4: Gustatory reception Taste = conscious perception produced by processing at the primary somatosensory cortex Information from taste buds is integrated with other sensory data Texture of food Taste-related sensations ( peppery or burning hot ) carried by trigeminal nerve (V) Taste receptors adapt slowly, but central adaptation reduces sensitivity to a new taste quickly Level of olfactory stimulation plays important role Several thousand times more sensitive to tastes when sense of smell is functioning

48 Module 15.4 Review A. What are gustducins? B. Identify the cranial nerves that carry gustatory information. C. Trace the gustatory pathway from the taste receptors to the cerebral cortex. Learning Outcome: Describe gustatory reception, briefly describe the physiological processes involved in taste, and trace the gustatory pathway.

49 Section 2: Vision Learning Outcomes 15.5 Outline the embryonic development of the eye Identify the accessory structures of the eye, and explain their functions Describe the layers of the eye wall and the anterior and posterior cavities of the eye Explain how light is directed to the fovea centralis of the retina Describe the process by which images are focused on the retina.

50 Section 2: Vision Learning Outcomes (continued) Describe the structure and function of the retina s layers of cells, and explain the distribution of rods and cones and their relation to visual acuity Describe the structure of the photoreceptors and how we are able to distinguish colors Explain photoreception and how visual pigments are activated.

51 Section 2: Vision Learning Outcomes (continued) Explain how the visual pathways distribute information to their destinations in the brain Clinical Module: Describe various refraction problems associated with the cornea, lens, or shape of the eye.

52 Module 15.5: The eyes form early in embryonic development Eyes are our most complex sense organs Much processing occurs in eye before relayed to CNS Resemble detached CNS nuclei that process visual stimuli Eye development 1. Begins as pair of bulges = optic vesicles Each contains cavity continuous with neural tube Form in prosencephalon walls

53 Module 15.5: Eye development Eye development (continued) 2. Lateral bulges indent; form optic cups connected to diencephalon Overlying epidermis forms pocket; pinches off to form the lens Inner and outer layers form retina Outer ependymal cells become photoreceptors Inner ependymal cells become pigment cells Nervous tissue of outer layer forms neurons, ganglion cells, specialized glial cells

54 Module 15.5: Eye development Eye development (continued) 3. Embryonic cells around optic cup form supporting layers of connective tissue Isolate nervous tissue Interior chambers develop; filled with fluid

55 Module 15.5: Review A. What are the first structures that form during eye development? B. Which structures develop into the retina? C. Which cells develop into the photoreceptors? Learning Outcome: Outline the embryonic development of the eye.

56 Module 15.6: Accessory structures of the eye provide protection while allowing light to reach the interior of the eye Eyelashes = robust hairs that keep foreign matter out of eyes Eyelids (palpebrae) = continuation of skin; can close to protect eye Blinking lubricates eye surface; clears dust/debris Medial angle of the eye = where two eyelids meet medially

57 Module 15.6: Eye accessory structures Lateral angle of the eye = where two eyelids meet laterally Palpebral fissure = gap between upper/lower eyelids

58 Module 15.6: Eye accessory structures Cornea = transparent area on anterior surface Pupil = opening in center of iris; transmits light Lacrimal caruncle = small, reddish body at medial angle Produces thick secretions that cause gritty deposits sometimes appearing after night s sleep

59 Module 15.6: Eye accessory structures Conjunctiva = mucous membrane and epithelium lining eyelids and covering anterior of eye Palpebral conjunctiva inner surface of eyelids Bulbar conjunctiva anterior eye surface; continuous with cornea Fornix = pocket created at junction of conjunctiva Tarsal glands = modified sebaceous glands Inner margin of eyelids Secretions prevent eyelid sticking

60 Module 15.6: Eye accessory structures Conjunctivitis, or pinkeye Inflammation of the conjunctiva Redness due to dilation of blood vessels deep to conjunctival epithelium From pathogenic infection or physical, allergic, or chemical irritation of conjunctival surface

61 Module 15.6: Eye accessory structures Lacrimal apparatus Lacrimal gland ~12 20 mm long Produces tears that lubricate, nourish, oxygenate, clean cornea Contain lysozyme and antibodies attack invading pathogens

62 Module 15.6: Eye accessory structures Lacrimal apparatus (continued) Tear ducts tubes; deliver tears from lacrimal gland to space behind upper eyelid (forming lacrimal lake ) Lacrimal puncta two small pores that drain the lacrimal lake Lacrimal canaliculi = connect lacrimal puncta to lacrimal sac

63 Module 15.6: Eye accessory structures Lacrimal apparatus (continued) Lacrimal sac = small chamber nestled in lacrimal sulcus of orbit Nasolacrimal duct From inferior tip of lacrimal sac through nasolacrimal canal Delivers tears to nasal cavity Empties into inferior meatus (inferior/ lateral to inferior nasal concha)

64 Module 15.6 Review A. Identify the accessory structures of the eye. B. Which layer of the eye would be the first affected by inadequate tear production? C. Describe conjunctivitis. Learning Outcome: Identify the accessory structures of the eye, and explain their functions.

65 Module 15.7: The hollow eyeball has a layered wall and fluid-filled anterior and posterior cavities Three layers (tunics) of the eye 1. Outer fibrous layer sclera, corneal limbus, and cornea 2. Middle vascular layer iris, choroid, ciliary body 3. Inner layer retina

66 Module 15.7: Eye layers and cavities Three layers (tunics) of the eye (continued) 1. Fibrous layer Outermost layer of eye Consists of cornea (clear) and sclera (white) Joined at corneoscleral junction Functions 1. Supports and protects the eye 2. Attachment site for extrinsic eye muscles 3. Curvature of the cornea aids in the focusing process (light first enters through cornea)

67 Module 15.7: Eye layers and cavities Three layers (tunics) of the eye (continued) 2. Vascular layer (uvea) contains many blood vessels, lymphatic vessels, and intrinsic (smooth) muscles of eye Includes iris, ciliary body, and choroid Functions 1. Provides route for blood vessels/lymphatics to eye tissues 2. Regulates amount of light entering eye (iris) 3. Secretes/reabsorbs aqueous humor (fluid) circulating in eye chambers 4. Controls shape of lens (ciliary body); essential for focusing

68 Module 15.7: Eye layers and cavities Three layers (tunics) of the eye (continued) Iris = colored part of eye Blood vessels, pigment cells (melanocytes) Two layers of smooth muscle contraction changes diameter of pupil to control amount of light entering Ciliary body = thickened region bulging into interior of eye Ring of fibers connects ciliary body and lens Choroid = vascular layer underlying sclera; has extensive capillary network supplying oxygen/ nutrients to neural layer

69 Module 15.7: Eye layers and cavities Three layers (tunics) of the eye (continued) 3. Inner layer, or retina = innermost layer of eye Outer pigmented layer absorbs light Thick, inner neural layer contains photoreceptors (the cells sensitive to light)

70 The three layers of the eye and associated structures

71 Module 15.7: Eye layers and cavities Eye cavities separated by lens/ciliary body Anterior cavity extends from cornea to lens; contains fluids called aqueous humor Two chambers 1. Anterior chamber cornea to iris 2. Posterior chamber (iris to ciliary body and lens) Posterior cavity is filled with gelatinous vitreous body Vitreous humor = fluid part of vitreous body

72 Module 15.7: Eye layers and cavities The anterior cavity Ciliary body 1. Ciliary muscle smooth muscle ring, projects inward 2. Ciliary processes folds of epithelium covering ciliary muscles 3. Ciliary zonule (suspensory ligaments) holds lens in position so light passes through it

73 Module 15.7: Eye layers and cavities The anterior cavity (continued) Aqueous humor Circulates within anterior cavity, passes through pupil Secreted by epithelial cells of ciliary processes Diffuses through vitreous body to retinal surface (vitreous humor)

74 Module 15.7: Eye layers and cavities Aqueous humor (continued) Leaves eye at scleral venous sinus (canal of Schlemm) = passageway around eye at level of corneoscleral junction Flows into veins in sclera Rate of removal should keep pace with rate of secretion

75 Module 15.7: Eye layers and cavities Aqueous humor (continued) Functions 1. Transports nutrients and wastes 2. Forms fluid cushion 3. Helps retain eye shape 4. Stabilizes position of the retina

76 Module 15.7: Eye layers and cavities Iris Body of iris is highly vascular, pigmented loose connective tissue Anterior surface incomplete layer of fibroblasts/melanocytes Posterior surface lined by pigmented epithelium of neural layer

77 Module 15.7: Eye layers and cavities Iris (continued) Oro serrata jagged edge of neural layer of retina Eye color determined by genes that influence density and distribution of melanocytes and density of pigmented epithelium

78 Module 15.7: Review A. Name the three layers of the eye. B. What give eyes their characteristic color? C. Where in the eye is aqueous humor located? Learning Outcome: Describe the layers of the eye wall and the anterior and posterior cavities of the eye.

79 Module 15.8: The structures of the eye direct light along a visual axis to the fovea centralis of the retina Cornea Allows light to enter eye transparent and clear Dense matrix of multiple layers of collagen fibers Avascular; receives oxygen and nutrients from tears

80 Module 15.8: Eye structures Lens Posterior to cornea; anchored by ciliary zonule of ciliary body, Concentric layers of cells filled with transparent crystallins = proteins responsible for clarity and focusing power of lens Dense fibrous capsule surrounds cells; blends with ciliary zonule Primary function: changes shape to focus image on photoreceptors

81 Module 15.8: Eye structures Choroid = middle layer; blood vessels nourish all eye structures Sclera ( white of the eye ) dense fibrous connective tissue with collagen and elastic fibers Stabilizes eye shape during movement Insertion for extrinsic eye muscles Optic nerve (II) conveys visual information to brain

82 Module 15.8: Eye structures Ciliary body supports lens, controls its shape; tension in ciliary zonule resists tendency of lens to ball up Retina contains photoreceptors, pigment cells, supporting cells, neurons

83 Module 15.8: Eye structures Pupil = opening in iris through which light passes Two pupillary muscles of iris regulate amount of light entering 1. Dilator pupillae muscles extend radially from pupil Enlarge pupil; supplied by sympathetic nervous system

84 Module 15.8: Eye structures 2. Sphincter pupillae muscles encircle pupil like a ring Make pupil smaller; supplied by parasympathetic nervous system

85 Action of the dilator pupillae muscle

86 Action of the sphincter pupillae muscle

87 Module 15.8: Eye structures Visual axis = imaginary line drawn from center of object you are looking at through the center of the cornea and lens to retina

88 Module 15.8: Eye structures Retina photoreceptors, pigment cells, supporting cells, neurons Photoreceptors in inner neural portion; type/density vary by area Macula patch of retina with high density of photoreceptors Fovea centralis central part of macula Has highest concentration of photoreceptors Point of sharpest vision

89 Review of structures of the eye

90 Module 15.8: Review A. Which eye structure does not contain blood vessels? B. What happens to the pupils when light intensity decreases? C. Light passing through the eye along the visual axis strikes what part of the retina? Learning Outcome: Explain how light is directed to the fovea centralis of the retina.

91 Module 15.9: Focusing of light produces a sharp image on the retina Focusing process is a two-step process 1. Light is refracted (bent) when it passes from air into cornea Bending occurs because of the change in density Amount of refraction at cornea is constant 2. More refraction when light passes from aqueous humor into lens Bends light rays toward focal point specific point on retina

92 Module 15.9: Focusing on the retina Focal distance of a lens Distance between center of lens and its focal point Determined by: 1. Distance from object to lens 2. Shape of lens Distance from lens to retina cannot change Focus by changing shape of the lens = accommodation

93 Module 15.9: Focusing on the retina Accommodation = change in lens shape to keep focal distance constant and provide clear vision For close vision: Ciliary muscle contracts ciliary body moves toward lens, reduces tension in ciliary zonule Lens pulled into more spherical shape; increases refraction Light from near objects is focused on retina

94 Module 15.9: Focusing on the retina Accommodation (continued) For distant vision: Ciliary muscle relaxes ciliary zonule pulls on lens Lens flattens; brings image of distant object into focus on retina

95 Module 15.9: Focusing on the retina Image formation Images are not single point, but rather consist of large numbers of individual points (like pixels on computer screen) each focused on retina Image is inverted and reversed; brain compensates learned from experience

96 Module 15.9: Focusing on the retina Near point of vision = inner limit of clear vision Determined by lens elasticity Increases with age as lens becomes less elastic In children 7 9 cm (3 4 in.) Young adult cm (6 8 in.) Age 60, about 83 cm (33 in.)

97 Module 15.16: Review A. Define focal point. B. When the ciliary muscles are relaxed, are you viewing something close up or something in the distance? C. Why does the near point of vision typically increase with age? Learning Outcome: Describe the process by which images are focused on the retina.

98 Module 15.10: The neural layer of the retina contains multiple layers of specialized photoreceptors, neurons, and supporting cells Retinal layers pigmented and neural layers Pigmented layer of the retina absorbs light that passes through neural part to prevent light bouncing back, producing visual echoes

99 Module 15.10: Retinal layers and cells Retinal layers (continued) Neural layer of the retina photoreceptors, supporting cells, neurons Preliminary processing/integration of visual information Photoreceptors located closest to pigmented layer

100 Module 15.10: Retinal layers and cells Retinal layers (continued) Ganglion cells innermost layer Axons converge at optic disc form optic nerve (optic disc also called blind spot lacks photoreceptors) Blood vessels follow optic nerve, supply inner neural layers cells

101 Module 15.10: Retinal layers and cells

102 Module 15.10: Retinal layers and cells Photoreceptors of the retina Rods Highly sensitive; allow vision in very dim light No color discrimination provide black-and-white vision only Cones Color vision Sharper, clearer images Require more intense light Rods and cones synapse with bipolar cells; bipolar cells synapse on ganglion cells

103 Photoreceptors of the retina

104 Module 15.10: Retinal layers and cells Horizontal and amacrine cells Facilitate/inhibit communication between photoreceptors and ganglion cells Horizontal cells where photoreceptors/bipolar cells synapse Amacrine cells where bipolar and ganglion cells synapse Alter sensitivity of retina; major role in adjusting to dim or bright light

105 Module 15.10: Retinal layers and cells Photoreceptor distribution Cones: ~6 million per eye Most dense at fovea centralis of macula no rods there Cone density directly correlates with visual acuity (sharpness) Rods: ~125 million per eye Maximum density at periphery; few cones there

106 Module 15.10: Review A. What is the eye s blind spot? B. Compare rods with cones. C. If you enter a dimly lit room, will you be able to see clearly? Why or why not? Learning Outcome: Describe the structure and function of the retina s layers of cells, and explain the distribution of rods and cones and their relation to visual acuity.

107 Module 15.11: Photoreception occurs in the outer segment of rod and cone cells Photoreceptors (rods and cones) detect photons (basic units of light) Light energy type of radiant energy that travels in waves Our visible spectrum: nm Visual pigments transduce light Derived from rhodopsin (visual purple); pigment in rods Have opsin (protein; determines wavelength absorbed) and retinal (pigment synthesized from vitamin A)

108 Module 15.11: Photoreception occurs in the outer segment of rod and cone cells Visual pigments transduce light Derived from rhodopsin (visual purple); pigment in rods Have opsin (protein; determines wavelength absorbed) and retinal (pigment synthesized from vitamin A)

109 Module 15.11: Photoreception Photoreceptor structure Pigmented epithelium adjacent to photoreceptors Absorbs photons not absorbed by visual pigments Phagocytizes old discs shed from tip of outer segment

110 Module 15.11: Photoreception Photoreceptor structure (continued) Outer segment Flattened, membranous discs containing visual pigment Cones: plasma membrane infoldings; outer segment tapers to blunt point Rods: discs are separate structures; outer segment forms elongated cylinder

111 Module 15.11: Photoreception Photoreceptor structure (continued) Inner segment Contains major organelles responsible for all cell functions other than photoreception Each photoreceptor synapses with a bipolar cell

112 Module 15.11: Photoreception Color vision Rods all contain same opsin; responds to bluegreen wavelengths Three types of cones 1. Blue cones (16% of cones) 2. Green cones (10%) 3. Red cones (74%)

113 Module 15.11: Photoreception Three cone types have different opsins; sensitive to different wavelength ranges, with overlap If all three types are stimulated equally, we see white

114 Module 15.11: Photoreception Color blindness nonfunctional cones Inability to distinguish certain colors One or more types of cones are nonfunctional absent or do not make necessary visual pigment Most common type is red green colorblindness no red cones; cannot distinguish between red and green Often inherited 10 percent of males 0.67 percent of females 1 in 300,000 no pigment

115 Module 15.11: Review A. Describe the structure of a photoreceptor. B. How could a diet deficient in vitamin A affect vision? C. Identify the three types of cones. Learning Outcome: Describe the structure of the photoreceptors and how we are able to distinguish colors.

116 Module 15.12: Photoreception involves activation, bleaching, and reassembly of visual pigments 1. Resting state (in the dark) Chemically gated sodium ion channels of outer segment stay open if cgmp present Inner segment continuously pumps sodium ions out of cytosol

117 Module 15.12: Photoreception process 1. Resting state (in the dark) (continued) This movement of ions = dark current Keeps resting membrane potential about 40 mv Photoreceptor continually releases neurotransmitters to bipolar cells

118 Module 15.12: Photoreception process 2. Retinal molecule in rhodopsin changes shape (activation) from a bent 11-cis form to more linear 11-trans form

119 Module 15.12: Photoreception process 3. Opsin activates transducin, a G protein bound to disc membrane Transducin activates phosphodiesterase (PDE)

120 Module 15.12: Photoreception process 4. Phosphodiesterase breaks down cgmp, inactivating gated sodium channels Sodium entry decreases

121 Module 15.12: Photoreception process Active state Decreased sodium entry reduces dark current Membrane potential drops to 70 mv (hyperpolarized)

122 Module 15.12: Photoreception process Active state (continued) Hyperpolarization decreases neurotransmitter release Decreased neurotransmitter signals bipolar cell that the photoreceptor has absorbed a photon

123 The process of photoreception

124 Module 15.12: Photoreception process Rhodopsin cannot respond to another photon until original shape of retinal is regained Three step process 1. Bleaching Entire rhodopsin molecule first broken into retinal and opsin 2. Retinal converted back to cis shape requires ATP 3. Opsin and retinal are reassembled as rhodopsin

125 Module Review A. What are the two configurations of retinal? B. Visual pigments undergo which three changes during photoreception? C. When during photoreception is ATP required? Learning Outcome: Explain photoreception and how visual pigments are activated.

126 Module 15.13: The visual pathways distribute visual information from each eye to both cerebral hemispheres Visual pathways Photoreceptors to bipolar cells to ganglion cells ~1 million axons from ganglion cell converge at optic disc; head toward diencephalon as the optic nerve (II)

127 Module 15.13: Visual pathways Visual pathways (continued) Two optic nerves (one from each eye) reach diencephalon at the optic chiasm From optic chiasm, continue along optic tracts About half of fibers go to lateral geniculate nucleus on same side of brain; other half go to opposite side

128 Module 15.13: Visual pathways Visual pathways (continued) Optic radiation = bundle of projection fibers linking each lateral geniculate body with visual cortex, in occipital cortex on same side Collaterals from fibers synapsing in lateral geniculate bodies go to subconscious processing centers in diencephalon and brainstem

129 Module 15.13: Visual pathways Visual pathways (continued) Pupillary reflexes and others are triggered by collaterals going to superior colliculi

130 Module 15.13: Visual pathways Perception of visual image reflects integration of information arriving at visual cortex Depth perception = ability to judge depth or distance by interpreting 3-D relationships Perceived by comparing relative positions of objects within images received by both eyes Visual images from left and right eyes overlap Each eye receives slightly different image due to: o Foveae centrales are cm (2 3 in.) apart o The nose and eye socket block view of opposite side

131 The visual pathway

132 Module Review A. Define optic radiation. B. Where are visual images perceived? Learning Outcome: Explain how the visual pathways distribute information to their destinations in the brain.

133 Module 15.14: Refractive problems result from abnormalities in the cornea or lens or in the shape of the eye Emmetropia = normal vision When ciliary muscle is relaxed and lens flattened, distant image is focused on retinal surface

134 Module 15.14: Refractive problems Myopia = nearsightedness Focal distance too short; image focuses in front of retina Eyeball too deep Resting curvature of lens too great Correct with diverging (concave) lens in front of eye Spreads light rays apart to shift focus forward onto retina

135 Module 15.14: Refractive problems Hyperopia = farsightedness Focal distance too long; image focuses beyond retina Eyeball too shallow Lens too flat Correct with converging (convex) lens in front of eye Provides additional refraction to focus on retina

136 Module 15.14: Refractive problems Surgical correction Photorefractive keratectomy (PRK) Computer-guided laser shapes cornea Removes µm (< 10%) of cornea Completed in less than a minute Laser-assisted in-situ keratomileusis (LASIK) Interior corneal layers reshaped; covered by normal corneal epithelium ~70% patients achieve normal vision ~10 million Americans have had it Immediate and long-term visual problems can occur

137 Module Review A. Define emmetropia. B. Which type of lens would correct hyperopia? Learning Outcome: Describe various refraction problems associated with the cornea, lens, or shape of the eye.

138 Section 3: Equilibrium and Hearing Learning Outcomes Describe the sensory receptors of the internal ear Describe the structures of the external, middle, and internal ear, and explain how they function Describe the structures and functions of the bony labyrinth and membranous labyrinth Describe the functions of hair cells in the semicircular ducts, utricle, and saccule Describe the structures and functions of the spiral organ.

139 Section 3: Equilibrium and Hearing Learning Outcomes (continued) Explain the anatomical and physiological basis for pitch and volume sensations for hearing Trace the pathways for the sensations of equilibrium and hearing to their respective destinations in the brain Clinical Module: Describe age-related disorders of olfaction, gustation, vision, equilibrium, and hearing.

140 Module 15.15: Equilibrium and hearing involve the internal ear Comparison of receptors Olfactory receptors specialized sensory neurons Gustatory receptors communicate with sensory neurons Photoreceptors respond to light Both route information directly to the CNS All located in epithelia exposed to external environment

141 Module 15.15: Internal ear sensory receptors Equilibrium and hearing receptors isolated and protected from external environment Located in internal ear Information integrated and organized locally; forwarded to CNS

142 Module 15.15: Internal ear sensory receptors Hair cells = sensory receptors in internal ear Free surfaces covered with specialized nonmotile processes Stereocilia resemble long microvilli; per hair cell Kinocilium = single large cilium

143 Module 15.15: Internal ear sensory receptors Hair cells are mechanoreceptors sensitive to contact/movement External force pushing on hair cell processes distorts plasma membrane; alters neurotransmitter release Provides information about direction/strength of stimulus Monitored by dendrites of sensory neurons

144 Module 15.15: Internal ear sensory receptors Complex 3-D structure in internal ear determines what stimuli can reach hair cells in each region Hair cells in one region respond only to gravity or acceleration Hair cells in other regions respond only to rotation or to sound

145 Module Review A. Contrast the olfactory and gustatory sensory receptors with those of equilibrium and hearing. B. Describe the sensory receptors of the internal ear. C. What kind of stimuli can the internal ear sense? Learning Outcome: Describe the sensory receptors of the internal ear.

146 Module 15.16: The ear is divided into the external ear, the middle ear, and the internal ear External ear collects/directs sound waves toward middle ear Auricle elastic cartilage External acoustic meatus passageway in temporal bone Ceruminous glands secrete waxy cerumen (earwax); keeps foreign objects out; slows growth of microorganisms Hairs trap debris

147 Module 15.16: Anatomy of the ear Middle ear (tympanic cavity) = air-filled chamber from tympanic membrane to auditory ossicles; connects to pharynx by auditory tube Tympanic membrane (tympanum, eardrum) = thin, semitransparent sheet that separates external ear and middle ear Auditory ossicles = three tiny bones; connect tympanic membrane and inner ear

148 Module 15.16: Anatomy of the ear Internal ear Contains sensory organs for hearing and equilibrium Receives amplified sound waves from middle ear Superficial contours established by layer of dense bone = bony labyrinth

149 The anatomy of the ear

150 Module 15.16: Anatomy of the ear Middle ear Auditory tube (pharyngotympanic tube, eustachian tube) Connects middle ear to nasopharynx Allows pressure equalization across tympanic membrane Can allow microorganisms into middle ear, causing infection (otitis media) can impair hearing, may invade internal ear

151 Module 15.16: Anatomy of the ear Auditory ossicles Malleus (malleus, hammer) attaches to tympanic membrane Incus (incus, anvil) attaches malleus to stapes Stapes (stapes, stirrup) attached to oval window

152 Module 15.16: Anatomy of the ear Middle ear muscles Tensor tympani muscle connects malleus to temporal bone Contraction stiffens tympanic membrane, reduces vibration Innervated by mandibular branch of trigeminal nerve (V)

153 Module 15.16: Anatomy of the ear Middle ear muscles (continued) Stapedius muscle Connects stapes to posterior wall of middle ear Reduces stapes movement at oval window

154 Structures of the middle ear

155 Module 15.16: Anatomy of the ear Amplification and protection Sound waves vibrate tympanic membrane; convert sound into mechanical movement Auditory ossicles conduct vibrations to internal ear Focuses sound on oval window and amplifies it Contractions of tensor tympani and stapedius muscles protect tympanic membrane and ossicles from violent movement under very noisy conditions

156 Module 15.6 Review A. Name the three tiny bones located in the middle ear, from lateral to medial. B. What is the function of the auditory tube? Learning Outcome: Describe the structures of the external, middle, and internal ear, and explain how they function.

157 Module 15.17: In the internal ear, the bony labyrinth protects the membranous labyrinth and its receptors Bony labyrinth = shell of dense bone surrounding/protecting membranous labyrinth Filled with perilymph = liquid similar to CSF; between bony labyrinth and membranous labyrinth Three parts 1. Semicircular canals 2. Vestibule 3. Cochlea

158 Module 15.17: Labyrinths of the internal ear Membranous labyrinth = collection of fluid-filled tubes/chambers Houses receptors for hearing and equilibrium Contains fluid called endolymph

159 Module 15.17: Labyrinths of the internal ear Three parts (semicircular canals, utricle, and saccule are part of the vestibular complex, which maintains equilibrium) 1. Semicircular ducts (within semicircular canals) Receptors stimulated by rotation of head 2. Within the vestibule utricle and saccule Provide sensations of gravity and linear acceleration 3. Cochlear duct (within cochlea) Sandwiched between pair of perilymph-filled chambers Resembles snail shell Receptors stimulated by sound

160 The anatomy of the internal ear

161 Module 15.17: Labyrinths of the internal ear The membranous labyrinth has four parts. The semicircular ducts, utricle, and saccule are part of the vestibular complex, which monitors equilibrium. The cochlear duct is responsible for hearing.

162 Module 15.7 Review A. Identify the structures of the bony labyrinth. B. How do the semicircular canals and the semicircular ducts differ? C. Describe the regional differences among the receptor complexes in the membranous labyrinth. Learning Outcome: Describe the structures and functions of the bony labyrinth and membranous labyrinth.

163 Module 15.18: Hair cells in the semicircular ducts respond to rotation; hair cells in the utricle and saccule respond to gravity and linear acceleration Semicircular ducts Three ducts (anterior, posterior, lateral) continuous with utricle and filled with endolymph Ampulla = enlarged part of duct that houses receptors

164 Module 15.18: Receptors for equilibrium Semicircular ducts (continued) Ampullary crest = region in wall of ampulla with receptors Ampullary cupula = gelatinous structure extending through ampulla with kinocilia and stereocilia of hair cells embedded in it

165 Module 15.18: Receptors for equilibrium Head rotating in plane of a duct moves endolymph; pushes ampullary cupula to side, distorting receptor processes Movement in one direction causes stimulation; opposite direction causes inhibition Ampullary cupula rebounds to normal position when endolymph stops moving

166 Module 15.18: Receptors for equilibrium Even complex angular movements can be analyzed by movement of the three rotational planes Horizontal rotation ( no ) stimulates lateral duct receptors Nodding ( yes ) stimulates anterior duct receptors Tilting head to side stimulates posterior duct receptors

167 Module 15.18: Receptors for equilibrium Utricle and saccule Provide equilibrium sensations, whether body is stationary or moving Connected by slender passageway continuous with endolymphatic duct that ends in endolymphatic sac Sac projects into subarachnoid space Endolymphatic duct continuously secretes endolymph; returns to general circulation at endolymphatic sac

168 Module 15.18: Receptors for equilibrium Utricle and saccule (continued) Utricle and saccule contain hair cells clustered in maculae Macula of utricle senses horizontal movement Macula of saccule senses vertical movement Hair cell processes embedded in gelatinous otolithic membrane Surface has densely packed calcium carbonate crystals (otoliths, or ear stones )

169 Module 15.18: Receptors for equilibrium Utricle and saccule (continued) Change in head position causes distortion of hair cell processes in the maculae, sending signals to the brain Head in upright position otoliths sit on top of otolithic membrane in utricle Head in tilted position or with linear movement gravity pulls on otoliths, shifts them to side Movement distorts hair cell processes; stimulates macular receptors

170 Module Review A. Define otoliths. B. Cite the functions of sensory receptors in the saccule and utricle. Learning Outcome: Describe the functions of hair cells in the semicircular ducts, utricle, and saccule.

171 Module 15.19: The cochlear duct contains the hair cells of the spiral organ that function in hearing Cochlear duct (scala media) Filled with endolymph Between two chambers with perilymph Scala vestibuli (vestibular duct) Scala tympani (tympanic duct) Encased by bony labyrinth except at oval/round windows Interconnect at tip of cochlear, forming single long chamber from oval window to round window

172 Module 15.19: Receptors for hearing Vestibular membrane separates cochlear duct/scala vestibule Basilar membrane separates cochlear duct from scala tympani Hair cells for hearing located in cochlear duct in the spiral organ (organ of Corti) on basilar membrane

173 Cross-sections of the cochlea

174 Module 15.19: Receptors for hearing Cross-sectional anatomy of cochlea Scala vestibuli and scala tympani filled with perilymph Cochlear duct filled with endolymph and contains spiral organ (with receptors for hearing) Spiral ganglion cell bodies of sensory neurons monitoring adjacent hair cells in spiral organ Axons from spiral ganglion in cochlear nerve of vestibulocochlear nerve (VIII)

175 Module 15.19: Receptors for hearing Spiral organ Hair cells lack kinocilia Stereocilia are in contact with overlying tectorial membrane Bulk of hair cell embedded in basilar membrane

176 Module 15.19: Receptors for hearing Spiral organ (continued) Sound waves create pressure waves in perilymph Pressure waves cause basilar membrane to vibrate up and down Vibrations of basilar membrane press stereocilia into tectorial membrane, distorting them

177 Module 15.19: Receptors for hearing Spiral organ (continued) Distortion triggers nerve impulse Sensory neurons relay signal through spiral ganglion to cochlear branch of vestibulocochlear nerve (VIII)

178 External and cross-sectional views of the cochlea

179 Anatomy of the spiral organ

180 A pressure wave in the perilymph causes movement of the hair cells and basilar membrane.

181 Module Review A. Where is the spiral organ located? B. Name the fluids found within the scala vestibuli, scala tympani, and cochlear duct. C. When the basilar membrane moves, what happens to the hair cells of the spiral organ? Learning Outcome: Describe the structures and functions of the spiral organ.

182 Module 15.20: Sound waves lead to movement of the basilar membrane in the process of hearing Hearing = perception of sound; sound = waves of pressure In air, pressure wave causes alternating areas of compressed/separated molecules Wavelength of sound = distance between adjacent wave crests (peaks) or adjacent troughs

183 Module 15.20: Physiology of hearing Sound waves travel at the same speed (speed of sound = 1235 km/h If frequency increases, wavelength decreases

184 Module 15.20: Physiology of hearing Frequency = number of waves (cycles) passing fixed point in given time Measured as cycles per second (cps); units = hertz (Hz) Wavelength and frequency inversely related Wavelength and frequency inversely related Pitch = our perception of frequency High frequency (short wavelength) = high pitch

185 Module 15.20: Physiology of hearing Intensity (loudness) = amount of energy in sound waves Amplitude of soundwave reflects amount of energy (intensity) Greater energy = larger amplitude = louder sound Measured in decibels (db)

186 Module 15.20: Physiology of hearing

187 Module 15.20: Physiology of hearing Sound waves and vibration Energy of sound waves is physical pressure Sound waves strike flexible object (i.e., tympanic membrane); object responds At particular frequency and amplitude, object will vibrate at same frequency = resonance Tympanic membrane resonates with sound waves, generating movement of stapes at oval window Basilar membrane regions resonate at different frequencies

188 Module 15.20: Physiology of hearing For hearing: Stapes pushes on the oval window Inward movement causes distortion of basilar membrane toward the round window Opposite action when stapes moves outward

189 Module 15.20: Physiology of hearing For hearing: (continued) Flexibility of basilar membrane varies along its length Different sound frequencies affect different parts of the membrane Location of vibration interpreted as pitch Number of stimulated hair cells interpreted as volume

190 The role of the basilar membrane in hearing

191 The role of the basilar membrane in hearing

192 The role of the basilar membrane in hearing

193 Module 15.20: Physiology of hearing

194 Module 15.20: Physiology of hearing

195 Module 15.20: Physiology of hearing

196 Module 15.20: Physiology of hearing

197 Module 15.20: Physiology of hearing

198 Module 15.20: Physiology of hearing

199 Module Review A. Define decibel. B. Beginning at the external acoustic meatus, list, in order, the structures involved in hearing. C. How would sound perception be affected if the round window could not bulge out as a result of increased perilymph pressure? Learning Outcome: Explain the anatomical and physiological basis for pitch and volume sensations for hearing.

200 Module 15.21: The vestibulocochlear nerve carries equilibrium and hearing sensations to the brainstem Equilibrium (balance)

201 Neural pathways for the sense of equilibrium

202 Neural pathways for the sense of equilibrium

203 Neural pathways for the sense of equilibrium

204 Neural pathways for the sense of equilibrium

205 Neural pathways for the sense of equilibrium

206 Module 15.21: Vestibulocochlear nerve function

207 Module 15.21: Vestibulocochlear nerve function Hearing Nerve signals for hearing are carried on the cochlear nerve, which is part of the vestibulocohlear nerve

208 Module 15.21: Vestibulocochlear nerve function Hearing Nerve signals for hearing are carried on the cochlear nerve, which is part of the vestibulocohlear nerve

209 Module 15.21: Vestibulocochlear nerve function Hearing (continued) Neural pathways for the sense of hearing

210 Module 15.21: Vestibulocochlear nerve function Hearing (continued) Neural pathways for the sense of hearing

211 Module 15.21: Vestibulocochlear nerve function Hearing (continued) Neural pathways for the sense of hearing

212 Module 15.21: Vestibulocochlear nerve function Hearing (continued) Neural pathways for the sense of hearing

213 Module 15.21: Vestibulocochlear nerve function Hearing (continued) Most auditory information from one cochlea is projected to the auditory cortex on opposite side Some information from cochlea reaches auditory cortex on its same side Aids in localizing sounds (left/right) Reduces functional impact of damage to one cochlea or ascending pathway

214 Module Review A. Where are the hair cell receptors for equilibrium located? B. Which cranial nerves are involved with eye, head, and neck movements? C. What is your reflexive response to hearing a loud noise, such as a firecracker? Learning Outcome: Trace the pathways for the sensations of equilibrium and hearing to their respective destinations in the brain.

215 Module 15.22: Aging is associated with many disorders of the special senses; trauma, infection, and abnormal stimuli may cause problems at any age Olfaction disorders Head injury damage to olfactory nerve (I) Age-related changes Olfactory receptors are regularly replaced by stem cells, but number declines with age Remaining receptors become less sensitive

216 Module 15.22: Disorders of the special senses Gustation disorders Problems with olfactory receptors decreased smell dulls taste Damaged taste buds mouth infection, inflammation Damaged cranial nerves (VII, IX, X) trauma or compression Natural age-related changes

217 Module 15.22: Disorders of the special senses Vision disorders Senile cataract lens loses transparency Natural consequence of aging; can be surgically corrected Progresses person needs more light to read; acuity may decline to blindness Presbyopia age-related farsightedness due to loss of lens elasticity (less accommodation possible for close vision)

218 Module 15.22: Disorders of the special senses Equilibrium disorders Vertigo false perception of spinning From conditions altering function of: Internal ear receptor complex Vestibular nerve (of vestibulocochlear nerve VIII) Sensory nuclei and CNS pathways Can be duo to vision problems or drug use (including alcohol)

219 Module 15.22: Disorders of the special senses Vertigo (continued) Stimulated by anything that sets endolymph in motion Motion sickness is most common cause Symptoms headache, sweating, flushing of face, nausea, vomiting

220 Module 15.22: Disorders of the special senses Hearing disorders Partial hearing deficit affects ~37.5 million in United States Two types: conductive and sensorineural Conductive hearing loss problem conducting sound waves Causes include impacted earwax, infection, perforated tympanic membrane