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17 The Special Senses PowerPoint® Lecture Presentations prepared by Jason LaPres Lone Star College—North Harris © 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. © 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. © 2012 Pearson Education, Inc. An Introduction to the Special Senses • Five Special Senses 1. Olfaction 2. Gustation 3. Vision 4. Equilibrium 5. Hearing © 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 © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) • Layers of Olfactory Organs • Olfactory epithelium contains: • Olfactory receptors • Supporting cells • Basal (stem) cells © 2012 Pearson Education, Inc. 17-1 Smell (Olfaction) • Layers of Olfactory Organs • Lamina propria contains: • Areolar tissue • Blood vessels • Nerves • Olfactory glands © 2012 Pearson Education, Inc. Figure 17-1a The Olfactory Organs Olfactory Pathway to the Cerebrum Olfactory Olfactory Olfactory epithelium nerve bulb fibers (N I) Olfactory tract Central nervous system Cribriform plate Superior nasal concha The olfactory organ on the left side of the nasal septum © 2012 Pearson Education, Inc. Figure 17-1b The Olfactory Organs Basal cell: divides to replace To worn-out olfactory olfactory receptor cells Olfactory bulb gland Cribriform plate Lamina propria Olfactory nerve fibers Developing olfactory receptor cell Olfactory receptor cell Olfactory epithelium Supporting cell Mucous layer Knob Subsance being smelled © 2012 Pearson Education, Inc. An olfactory receptor is a modified neuron with multiple cilia extending from its free surface. Olfactory cilia: surfaces contain receptor proteins (see Spotlight Fig. 173) 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 © 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 © 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 © 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 © 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. Action potentials Stimulus removed Stimulus Dendrites Specialized olfactory neuron Stimulus Threshold Generator potential © 2012 Pearson Education, Inc. to CNS Figure 17-2 Olfactory and Gustatory Receptors Olfactory reception occurs on the surface membranes of the olfactory cilia. Odorantsdissolved chemicals that stimulate olfactory receptorsinteract with receptors called odorant- binding proteins on the membrane surface. 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). Odorant molecule Inactive enzyme MUCOUS LAYER 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. The cAMP then opens sodium channels in the plasma membrane, which, as a result, begins to depolarize. Closed sodium channel Depolarized membrane Active enzyme RECEPTOR CELL © 2012 Pearson Education, Inc. If sufficient depolarization occurs, an action potential is triggered in the axon, and the information is relayed to the CNS. Sodium ions enter 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 © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) • Taste Buds • Associated with epithelial projections (lingual papillae) on superior surface of tongue © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-3a Gustatory Receptors Water receptors (pharynx) Umami Sour Bitter Salty Sweet Landmarks and receptors on the tongue © 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. © 2012 Pearson Education, Inc. Figure 17-3c Gustatory Receptors Taste buds Taste buds LM 280 Taste bud LM 650 Nucleus of transitional cell Nucleus of gustatory cell Nucleus of basal cell 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. © 2012 Pearson Education, Inc. 17-2 Taste (Gustation) • Gustatory Discrimination • Four primary taste sensations 1. Sweet 2. Salty 3. Sour 4. Bitter © 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 © 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 © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-2 Olfactory and Gustatory Receptors Receptor cell Stimulus Stimulus removed Stimulus Threshold Receptor cell Receptor depolarization Synapse Axon of sensory neuron Axon Stimulus Action potentials Synaptic delay to CNS Generator potential © 2012 Pearson Education, Inc. Figure 17-2 Olfactory and Gustatory Receptors Salt and Sour Receptors Sweet, Bitter, and Umami Receptors Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell. 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. Sour, salt Gated ion channel Sweet, bitter, or umami Membrane receptor Resting plasma membrane Inactive G protein Active G protein Channel opens Depolarized membrane Active G protein Active 2nd messenger Depolarization of membrane stimulates release of chemical neurotransmitters. © 2012 Pearson Education, Inc. Inactive 2nd messenger Activation of second messengers stimulates release of chemical neurotransmitters. 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 © 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 © 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 © 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 © 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) © 2012 Pearson Education, Inc. Figure 17-4a External Features and Accessory Structures of the Eye Eyelashes Pupil Lateral canthus Palpebra Palpebral fissure Sclera Medial canthus Lacrimal caruncle Corneal limbus Gross and superficial anatomy of the accessory structures © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-4b External Features and Accessory Structures of the Eye Superior Tendon of superior rectus muscle oblique muscle Lacrimal gland ducts Lacrimal punctum Lacrimal gland Lacrimal caruncle Ocular conjunctiva Superior lacrimal canaliculus Medial canthus Inferior lacrimal canaliculus Lacrimal sac Lateral canthus Lower eyelid Orbital fat Inferior rectus muscle Nasolacrimal duct Inferior oblique muscle Inferior nasal concha Opening of nasolacrimal duct The organization of the lacrimal apparatus. © 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 © 2012 Pearson Education, Inc. 17-3 The Eye • Eyeball • Is hollow • Is divided into two cavities 1. Large posterior cavity 2. Smaller anterior cavity © 2012 Pearson Education, Inc. Figure 17-5a The Sectional Anatomy of the Eye Fornix Palpebral conjunctiva Eyelash Ocular conjunctiva Optic nerve Ora serrata Cornea Lens Pupil Iris Limbus Fovea Retina Choroid Sclera Sagittal section of left eye © 2012 Pearson Education, Inc. Figure 17-5b The Sectional Anatomy of the Eye Fibrous layer Cornea Anterior cavity Sclera Vascular layer (uvea) Iris Ciliary body Choroid Neural layer (retina) Posterior cavity Neural part Pigmented part Horizontal section of right eye © 2012 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Posterior Anterior Edge of pupil chamber chamber Iris Suspensory ligament of lens Nose Corneal limbus Conjunctiva Lacrimal punctum Lacrimal caruncle Lower eyelid Medial canthus Ciliary processes Lateral canthus Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye © 2012 Pearson Education, Inc. 17-3 The Eye • The Fibrous Layer • Sclera (white of the eye) • Cornea • Corneal limbus (border between cornea and sclera) © 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 © 2012 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Posterior Anterior Edge of pupil chamber chamber Iris Suspensory ligament of lens Nose Corneal limbus Conjunctiva Lacrimal punctum Lacrimal caruncle Lower eyelid Medial canthus Ciliary processes Lateral canthus Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye © 2012 Pearson Education, Inc. 17-3 The Eye • The Vascular Layer • Iris • Contains papillary muscles • Change diameter of pupil © 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 © 2012 Pearson Education, Inc. The pupillary constrictor muscles form a series of concentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases. Increased light intensity Increased parasympathetic stimulation 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 © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Posterior Anterior Edge of pupil chamber chamber Iris Suspensory ligament of lens Nose Corneal limbus Conjunctiva Lacrimal punctum Lacrimal caruncle Lower eyelid Medial canthus Ciliary processes Lateral canthus Lens Ciliary body Ora serrata Sclera Choroid Retina Posterior cavity Ethmoidal labyrinth Lateral rectus muscle Medial rectus muscle Optic disc Fovea Optic nerve Orbital fat Central artery and vein Horizontal dissection of right eye © 2012 Pearson Education, Inc. Figure 17-7a The Organization of the Retina Horizontal cell Cone Rod Pigmented part of retina Rods and cones Amacrine cell 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). © 2012 Pearson Education, Inc. Figure 17-7a The Organization of the Retina Choroid Pigmented part of retina Rods and cones Bipolar cells Ganglion cells Retina LM 350 Nuclei of Nuclei of rods Nuclei of ganglion cells and cones bipolar cells The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). © 2012 Pearson Education, Inc. Figure 17-7b The Organization of the Retina Pigmented Neural part part of retina of retina Central retinal vein Optic disc Central retinal artery Sclera Optic nerve © 2012 Pearson Education, Inc. Choroid The optic disc in diagrammatic sagittal section. Figure 17-7c The Organization of the Retina Fovea Macula Optic disc (blind spot) Central retinal artery and vein emerging from center of optic disc A photograph of the retina as seen through the pupil. © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-8 A Demonstration of the Presence of a Blind Spot © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-9 The Circulation of Aqueous Humor Cornea Anterior cavity Pupil Anterior chamber Scleral venous sinus Posterior chamber Body of iris Ciliary process Lens Suspensory ligaments Pigmented epithelium Conjunctiva Ciliary body Sclera Posterior cavity (vitreous chamber) Choroid Retina © 2012 Pearson Education, Inc. 17-3 The Eye • Large Posterior Cavity (Vitreous Chamber) • Vitreous body • Gelatinous mass • Helps stabilize eye shape and supports retina © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-10 Factors Affecting Focal Distance Focal distance Focal distance Close source Light from distant source (object) Focal distance Focal point Lens The closer the light source, the longer the focal distance © 2012 Pearson Education, Inc. The rounder the lens, the shorter the focal distance 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 © 2012 Pearson Education, Inc. Figure 17-11 Accommodation For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed © 2012 Pearson Education, Inc. Figure 17-11a Accommodation For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted © 2012 Pearson Education, Inc. Figure 17-11b Accommodation For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed © 2012 Pearson Education, Inc. 17-3 The Eye • Light Refraction of Lens • Image reversal • Visual acuity • Clarity of vision • “Normal” rating is 20/20 © 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. © 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. © 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.) © 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 representations are not drawn to scale.) © 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. © 2012 Pearson Education, Inc. A camera lens has a fixed size and shape and focuses by varying the distance to the film. Figure 17-13 Accommodation Problems Emmetropia (normal vision) © 2012 Pearson Education, Inc. Figure 17-13 Accommodation Problems Myopia (nearsightedness) 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 corrected with a diverging, concave lens Diverging lens © 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 © 2012 Pearson Education, Inc. Converging lens 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. © 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 © 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 © 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 © 2012 Pearson Education, Inc. Figure 17-14a Structure of Rods, Cones, and Rhodopsin Molecule Pigment Epithelium 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. Melanin granules Outer Segment Discs Connecting stalks Inner Segment Mitochondria Golgi apparatus Nuclei Cone Rods Each photoreceptor synapses with a bipolar cell. Bipolar cell LIGHT Structure of rods and cones. © 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 Retinal Opsin Structure of rhodospin molecule. © 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 © 2012 Pearson Education, Inc. Figure 17-15 Cone Types and Sensitivity to Color Rods Light absorption (percent of maximum) Blue cones Red Green cones cones W A V E L E N G T H (nm) Violet © 2012 Pearson Education, Inc. Blue Green Yellow Orange Red Figure 17-16 A Standard Test for Color Vision © 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 © 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. Photon Rhodopsin 11-cis retinal 11-trans retinal Opsin 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. © 2012 Pearson Education, Inc. Figure 17-17 Photoreception Opsin activates transducin, which in turn activates phosphodiestease (PDE) Transducin is a G proteina membrane-bound enzyme complex PDE Transducin Disc membrane © 2012 Pearson Education, Inc. In this case, transducin is activated by opsin, and transducin in turn activates phosphodiesterase (PDE). Figure 17-17 Photoreception Cyclic-GMP levels decline and gated sodium channels close Phosphodiesterase is an enzyme that breaks down cGMP. GMP cGMP © 2012 Pearson Education, Inc. The removal of cGMP from the gated sodium channels results in their inactivation. The rate of Na entry into the cytoplasm is then decreased. Figure 17-17 Photoreception ACTIVE STATE IN LIGHT Dark current is reduced and rate of neurotransmitter release declines © 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 © 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. 11-trans retinal 11-cis retinal and opsin are reassembled to form rhodopsin. 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. Photon ADP ATP enzyme Opsin 11-cis retinal The retinal is converted to its original shape. This conversion requires energy in the form of ATP. © 2012 Pearson Education, Inc. 11-trans retinal Opsin After absorbing a photon, the rhodopsin molecule begins to break down into retinal and opsin, a process known as bleaching. 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. 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. Na Na Neurotransmitter release Bipolar cell Ganglion cell 17-4 Visual Physiology • Light and Dark Adaptation • Dark • Most visual pigments are fully receptive to stimulation • Light • Pupil constricts • Bleaching of visual pigments occurs © 2012 Pearson Education, Inc. 17-4 Visual Physiology • The Visual Pathways • Begin at photoreceptors • End at visual cortex of cerebral hemispheres • Message crosses two synapses before it heads toward brain • Photoreceptor to bipolar cell • Bipolar cell to ganglion cell © 2012 Pearson Education, Inc. 17-4 Visual Physiology • Ganglion Cells • Monitor a specific portion of a field of vision • M Cells • Are ganglion cells that monitor rods • Are relatively large • Provide information about: • General form of object • Motion • Shadows in dim lighting © 2012 Pearson Education, Inc. 17-4 Visual Physiology • Ganglion Cells • P cells • Are ganglion cells that monitor cones • Are smaller, more numerous • Provide information about edges, fine detail, and color © 2012 Pearson Education, Inc. 17-4 Visual Physiology • Ganglion Cells • On-center neurons • Are excited by light arriving in center of their sensory field • Are inhibited when light strikes edges of their receptive field • Off-center neurons • Inhibited by light in central zone • Stimulated by illumination at edges © 2012 Pearson Education, Inc. Figure 17-19 Convergence and Ganglion Cell Function Retinal surface (contacts pigment epithelium) Receptive field of ganglion cell Receptive field Photoreceptors Horizontal cell Bipolar cell Amacrine cell Ganglion cell © 2012 Pearson Education, Inc. 17-4 Visual Physiology • Central Processing of Visual Information • Axons from ganglion cells converge on optic disc • Penetrate wall of eye • Proceed toward diencephalon as optic nerve (II) • Two optic nerves (one for each eye) reach diencephalon at optic chiasm © 2012 Pearson Education, Inc. 17-4 Visual Physiology • Visual Data • From combined field of vision arrive at visual cortex of opposite occipital lobe • Left half arrive at right occipital lobe • Right half arrive at left occipital lobe • Optic radiation • Bundle of projection fibers linking lateral geniculate with visual cortex © 2012 Pearson Education, Inc. 17-4 Visual Physiology • The Field of Vision • Depth perception • Obtained by comparing relative positions of objects between left-eye and right-eye images © 2012 Pearson Education, Inc. 17-4 Visual Physiology • The Brain Stem and Visual Processing • Circadian rhythm • Is tied to day-night cycle • Affects other metabolic processes © 2012 Pearson Education, Inc. Figure 17-20 The Visual Pathways Combined Visual Field Left side Left eye only Right side Binocular vision Right eye only The Visual Pathway Photoreceptors in retina Retina Optic disc Optic nerve (N II) Optic chiasm Optic tract Lateral geniculate nucleus Diencephalon and brain stem Suprachiasmatic nucleus Projection fibers (optic radiation) Visual cortex of cerebral hemispheres © 2012 Pearson Education, Inc. Left cerebral hemisphere Superior colliculus Right cerebral hemisphere 17-5 The Ear • The External Ear • Auricle • Surrounds entrance to external acoustic meatus • Protects opening of canal • Provides directional sensitivity © 2012 Pearson Education, Inc. 17-5 The Ear • The External Ear • External acoustic meatus • Ends at tympanic membrane (eardrum) • Tympanic membrane • Is a thin, semitransparent sheet • Separates external ear from middle ear © 2012 Pearson Education, Inc. Figure 17-21 The Anatomy of the Ear Middle Ear External Ear Elastic cartilages Internal Ear Auditory ossicles Oval window Semicircular canals Petrous part of temporal bone Auricle Facial nerve (N VII) Vestibulocochlear nerve (N VIII) Bony labyrinth of internal ear Cochlea Tympanic cavity Auditory tube To nasopharynx External acoustic meatus © 2012 Pearson Education, Inc. Tympanic membrane Round Vestibule window 17-5 The Ear • The External Ear • Ceruminous glands • Integumentary glands along external acoustic meatus • Secrete waxy material (cerumen) • Keeps foreign objects out of tympanic membrane • Slows growth of microorganisms in external acoustic meatus © 2012 Pearson Education, Inc. 17-5 The Ear • The Middle Ear • Also called tympanic cavity • Communicates with nasopharynx via auditory tube • Permits equalization of pressures on either side of tympanic membrane • Encloses and protects three auditory ossicles 1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup) © 2012 Pearson Education, Inc. Figure 17-22a The Middle Ear Auditory Ossicles Malleus Incus Stapes Temporal bone (petrous part) Stabilizing ligaments Oval window Branch of facial nerve VII (cut) Tensor tympani muscle External acoustic meatus Stapedius muscle Tympanic cavity (middle ear) Tympanic membrane Round window Auditory tube The structures of the middle ear. © 2012 Pearson Education, Inc. Muscles of the Middle Ear Figure 17-22b The Middle Ear Malleus attached to tympanic membrane Malleus Tendon of tensor tympani muscle Incus Base of stapes at oval window Stapes Stapedius muscle Inner surface of tympanic membrane The tympanic membrane and auditory ossicles © 2012 Pearson Education, Inc. 17-5 The Ear • Vibration of Tympanic Membrane • Converts arriving sound waves into mechanical movements • Auditory ossicles conduct vibrations to inner ear • Tensor tympani muscle • Stiffens tympanic membrane • Stapedius muscle • Reduces movement of stapes at oval window © 2012 Pearson Education, Inc. 17-5 The Ear • The Internal Ear • Contains fluid called endolymph • Bony labyrinth surrounds and protects membranous labyrinth • Subdivided into: • Vestibule • Semicircular canals • Cochlea © 2012 Pearson Education, Inc. Figure 17-23b The Internal Ear KEY Membranous labyrinth Semicircular ducts Anterior Lateral Posterior Bony labyrinth Vestibule Cristae within ampullae Maculae Endolymphatic sac Semicircular canal Cochlea Utricle Saccule Vestibular duct Cochlear duct Tympanic Spiral duct organ The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple. © 2012 Pearson Education, Inc. Figure 17-23a The Internal Ear Perilymph Bony labyrinth Endolymph Membranous labyrinth A section through one of the semicircular canals, showing the relationship between the bony and membranous labyrinths, and the boundaries of perilymph and endolymph. © 2012 Pearson Education, Inc. KEY Membranous labyrinth Bony labyrinth 17-5 The Ear • The Internal Ear • Vestibule • Encloses saccule and utricle • Receptors provide sensations of gravity and linear acceleration • Semicircular canals • Contain semicircular ducts • Receptors stimulated by rotation of head © 2012 Pearson Education, Inc. 17-5 The Ear • The Internal Ear • Cochlea • Contains cochlear duct (elongated portion of membranous labyrinth) • Receptors provide sense of hearing © 2012 Pearson Education, Inc. 17-5 The Ear • The Internal Ear • Round window • Thin, membranous partition • Separates perilymph from air spaces of middle ear • Oval window • Formed of collagen fibers • Connected to base of stapes © 2012 Pearson Education, Inc. 17-5 The Ear • Stimuli and Location • Sense of gravity and acceleration • From hair cells in vestibule • Sense of rotation • From semicircular canals • Sense of sound • From cochlea © 2012 Pearson Education, Inc. 17-5 The Ear • Equilibrium • Sensations provided by receptors of vestibular complex • Hair cells • Basic receptors of inner ear • Provide information about direction and strength of mechanical stimuli © 2012 Pearson Education, Inc. 17-5 The Ear • The Semicircular Ducts • Are continuous with utricle • Each duct contains: • Ampulla with gelatinous cupula • Associated sensory receptors • Stereocilia – resemble long microvilli • Are on surface of hair cell • Kinocilium – single large cilium © 2012 Pearson Education, Inc. Figure 17-24a The Semicircular Ducts Vestibular branch (N VIII) Semicircular ducts Anterior Posterior Lateral Cochlea Ampulla Endolymphatic sac Endolymphatic duct Utricle Saccule Maculae An anterior view of the right semicircular ducts, the utricle, and the saccule, showing the locations of sensory receptors © 2012 Pearson Education, Inc. Figure 17-24b The Semicircular Ducts Ampulla filled with endolymph Cupula Hair cells Crista Supporting cells Sensory nerve A cross section through the ampulla of a semicircular duct © 2012 Pearson Education, Inc. Figure 17-24c The Semicircular Ducts Direction of relative endolymph movement Direction of duct rotation Semicircular duct Ampulla At rest Endolymph movement along the length of the duct moves the cupula and stimulates the hair cells. © 2012 Pearson Education, Inc. Direction of duct rotation Figure 17-24d The Semicircular Ducts Displacement in this direction stimulates hair cell Kinocilium Displacement in this direction inhibits hair cell Stereocilia Hair cell Sensory nerve ending Supporting cell © 2012 Pearson Education, Inc. A representative hair cell (receptor) from the vestibular complex. Bending the sterocilia toward the kinocilium depolarizes the cell and stimulates the sensory neuron. Displacement in the opposite direction inhibits the sensory neuron. 17-5 The Ear • The Utricle and Saccule • Provide equilibrium sensations • Are connected with the endolymphatic duct, which ends in endolymphatic sac © 2012 Pearson Education, Inc. 17-5 The Ear • The Utricle and Saccule • Maculae • Oval structures where hair cells cluster • Statoconia • Densely packed calcium carbonate crystals on surface of gelatinous mass • Otolith (ear stone) = gelatinous matrix and statoconia © 2012 Pearson Education, Inc. Figure 17-25ab The Saccule and Utricle The location of the maculae Gelatinous material Statoconia Hair cells Nerve fibers The structure of an individual macula © 2012 Pearson Education, Inc. Otolith Figure 17-25c The Saccule and Utricle Head in normal, upright position Gravity Head tilted posteriorly Receptor output increases Gravity Otolith moves “downhill,” distorting hair cell processes A diagrammatic view of macular function when the head is held horizontally 1 and then tilted back 2 © 2012 Pearson Education, Inc. 17-5 The Ear • Pathways for Equilibrium Sensations • Vestibular receptors • Activate sensory neurons of vestibular ganglia • Axons form vestibular branch of vestibulocochlear nerve (VIII) • Synapse within vestibular nuclei © 2012 Pearson Education, Inc. 17-5 The Ear • Four Functions of Vestibular Nuclei 1. Integrate sensory information about balance and equilibrium from both sides of head 2. Relay information from vestibular complex to cerebellum 3. Relay information from vestibular complex to cerebral cortex • Provide conscious sense of head position and movement 4. Send commands to motor nuclei in brain stem and spinal cord © 2012 Pearson Education, Inc. Figure 17-26 Pathways for Equilibrium Sensations To superior colliculus and relay to cerebral cortex Red nucleus N III Vestibular ganglion N IV Vestibular branch Semicircular canals Vestibular nucleus N VI To cerebellum Vestibule Cochlear branch N XI Vestibulocochlear nerve (N VIII) Vestibulospinal tracts © 2012 Pearson Education, Inc. 17-5 The Ear • Eye, Head, and Neck Movements • Reflexive motor commands • From vestibular nuclei • Distributed to motor nuclei for cranial nerves • Peripheral Muscle Tone, Head, and Neck Movements • Instructions descend in vestibulospinal tracts of spinal cord © 2012 Pearson Education, Inc. 17-5 The Ear • Eye Movements • Sensations of motion directed by superior colliculi of the midbrain • Attempt to keep focus on specific point • If spinning rapidly, eye jumps from point to point • Nystagmus • Have trouble controlling eye movements • Caused by damage to brain stem or inner ear © 2012 Pearson Education, Inc. 17-5 The Ear • Hearing • Cochlear duct receptors • Provide sense of hearing © 2012 Pearson Education, Inc. Figure 17-27a The Cochlea Round window Stapes at oval window Scala vestibuli Cochlear duct Scala tympani Semicircular canals Cochlear branch Vestibular branch Vestibulocochlear nerve (N VIII) The structure of the cochlea © 2012 Pearson Education, Inc. KEY From oval window to tip of spiral From tip of spiral to round window Figure 17-27b The Cochlea Temporal bone (petrous part) Vestibular membrane Scala vestibuli (contains perilymph) Tectorial membrane Cochlear duct (contains endolymph) Basilar membrane Spiral organ From oval window Spiral ganglion Scala tympani (contains perilymph) To round window Cochlear nerve Vestibulocochlear nerve (N VIII) Diagrammatic and sectional views of the cochlear spiral © 2012 Pearson Education, Inc. Figure 17-27b The Cochlea Vestibular membrane Basilar membrane Temporal bone (petrous part) Scala vestibuli (contains perilymph) Cochlear duct (contains endolymph) Spiral organ Spiral ganglion Scala tympani (contains perilymph) Cochlear nerve Cochlear spiral section Diagrammatic and sectional views of the cochlear spiral © 2012 Pearson Education, Inc. LM 60 17-5 The Ear • Hearing • Auditory ossicles • Convert pressure fluctuation in air into much greater pressure fluctuations in perilymph of cochlea • Frequency of sound • Determined by which part of cochlear duct is stimulated • Intensity (volume) • Determined by number of hair cells stimulated © 2012 Pearson Education, Inc. 17-5 The Ear • Hearing • Cochlear duct receptors • Basilar membrane • Separates cochlear duct from tympanic duct • Hair cells lack kinocilia • Stereocilia in contact with overlying tectorial membrane © 2012 Pearson Education, Inc. Figure 17-28a The Spiral Organ Body cochlear wall Scala vestibuli Vestibular membrane Cochlear duct Tectorial membrane Spiral ganglion Basilar membrane Scala tympani Spiral organ A three-dimensional section of the cochlea, showing the compartments, tectorial membrane, and spiral organ © 2012 Pearson Education, Inc. Cochlear branch of N VIII Figure 17-28b The Spiral Organ Tectorial membrane Outer hair cell Basilar membrane Inner hair cell Nerve fibers Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ © 2012 Pearson Education, Inc. Figure 17-28b The Spiral Organ Cochlear duct (scala media) Vestibular membrane Tectorial membrane Scala tympani Spiral organ Basilar Hair cells Spiral ganglion cells of membrane of spiral organ cochlear nerve LM 125 Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ © 2012 Pearson Education, Inc. 17-5 The Ear • An Introduction to Sound • Pressure Waves • Consist of regions where air molecules are crowded together • Adjacent zone where molecules are farther apart • Sine waves • S-shaped curves © 2012 Pearson Education, Inc. 17-5 The Ear • Pressure Wave • Wavelength • Distance between two adjacent wave troughs • Frequency • Number of waves that pass fixed reference point at given time • Physicists use term cycles instead of waves • Hertz (Hz) number of cycles per second (cps) © 2012 Pearson Education, Inc. 17-5 The Ear • Pressure Wave • Pitch • Our sensory response to frequency • Amplitude • Intensity of sound wave • Sound energy is reported in decibels © 2012 Pearson Education, Inc. Figure 17-29a The Nature of Sound Wavelength Tympanic membrane Tuning fork Air molecules Sound waves (here, generated by a tuning fork) travel through the air as pressure waves. © 2012 Pearson Education, Inc. Figure 17-29b The Nature of Sound 1 wavelength Amplitude A graph showing the sound energy arriving at the tympanic membrane. The distance between wave peaks is the wavelength. The number of waves arriving each second is the frequency, which we perceive as pitch. Frequencies are reported in cycles per second (cps), or hertz (Hz). The amount of energy in each wave determines the wave’s amplitude, or intensity, which we perceive as the loudness of the sound. © 2012 Pearson Education, Inc. Figure 17-31a Frequency Discrimination Stapes at oval window Cochlea 16,000 Hz Round window 6000 Hz 1000 Hz Basilar membrane The flexibility of the basilar membrane varies along its length, so pressure waves of different frequencies affect different parts of the membrane. © 2012 Pearson Education, Inc. Figure 17-31b Frequency Discrimination Stapes moves inward Round window pushed outward Basilar membrane distorts toward round window The effects of a vibration of the stapes at a frequency of 6000 Hz. When the stapes moves inward, as shown here, the basilar membrane distorts toward the round window, which bulges into the middle-ear cavity. © 2012 Pearson Education, Inc. Figure 17-31c Frequency Discrimination Stapes moves outward Round window pulled inward Basilar membrane distorts toward oval window When the stapes moves outward, as shown here, the basilar membrane rebounds and distorts toward the oval window. © 2012 Pearson Education, Inc. Figure 17-30 Sound and Hearing External acoustic meatus Malleus Incus Stapes Oval window Movement of sound waves Tympanic membrane Sound waves arrive at tympanic membrane. © 2012 Pearson Education, Inc. Movement of the tympanic membrane causes displacement of the auditory ossicles. Round window Movement of the stapes at the oval window establishes pressure waves in the perilymph of the scala vestibuli. Figure 17-30 Sound and Hearing Cochlear branch of cranial nerve VIII Scala vestibuli (contains perilymph) Vestibular membrane Cochlear duct (contains endolymph) Basilar membrane Scala tympani (contains perilymph) The pressure waves distort the basilar membrane on their way to the round window of the scala tympani. © 2012 Pearson Education, Inc. Vibration of the basilar membrane causes vibration of hair cells against the tectorial membrane. Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII. 17-5 The Ear • Auditory Pathways • Cochlear branch • Formed by afferent fibers of spiral ganglion neurons • Enters medulla oblongata • Synapses at dorsal and ventral cochlear nuclei • Information crosses to opposite side of brain • Ascends to inferior colliculus of midbrain © 2012 Pearson Education, Inc. 17-5 The Ear • Auditory Pathways • Ascending auditory sensations • Synapse in medial geniculate nucleus of thalamus • Projection fibers deliver information to auditory cortex of temporal lobe © 2012 Pearson Education, Inc. Figure 17-32 Pathways for Auditory Sensations Stimulation of hair cells at a specific location along the basilar membrane activates sensory neurons. KEY Primary pathway Secondary pathway Motor output Cochlea Low-frequency sounds High-frequency sounds Vestibular branch Sensory neurons carry the sound information in the cochlear branch of the vestibulocochlear nerve (VIII) to the cochlear nucleus on that side. © 2012 Pearson Education, Inc. Vestibulocochlear nerve (VIII) Figure 17-32 Pathways for Auditory Sensations Projection fibers then deliver the information to specific locations within the auditory cortex of the temporal lobe. Highfrequency sounds Thalamus Low-frequency sounds Ascending acoustic information goes to the medial geniculate nucleus. The inferior colliculi direct a variety of unconscious motor responses to sounds. To cerebellum To reticular formation and motor nuclei of cranial nerves Information ascends from each cochlear nucleus to the inferior colliculi of the midbrain. KEY Motor output to spinal cord through the tectospinal tracts © 2012 Pearson Education, Inc. Primary pathway Secondary pathway Motor output 17-5 The Ear • Hearing Range • From softest to loudest represents trillionfold increase in power • Never use full potential • Young children have greatest range © 2012 Pearson Education, Inc. Table 17-1 Intensity of Representative Sounds © 2012 Pearson Education, Inc. 17-5 The Ear • Effects of Aging on the Ear • With age, damage accumulates • Tympanic membrane gets less flexible • Articulations between ossicles stiffen • Round window may begin to ossify © 2012 Pearson Education, Inc.
