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Chapter 17 The Special Senses Lecture Presentation by Lee Ann Frederick University of Texas at Arlington © 2015 Pearson Education, Inc. An Introduction to the Special Senses • Five Special Senses 1. 2. 3. 4. 5. Olfaction Gustation Vision Equilibrium Hearing © 2015 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 © 2015 Pearson Education, Inc. Figure 17-1a The Olfactory Organs. Olfactory Pathway to the Cerebrum Olfactory epithelium Olfactory nerve fibers (N I) Olfactory bulb Olfactory tract Central nervous system Cribriform plate Superior nasal concha a The olfactory organ on the right © 2015 Pearson Education, Inc. side of the nasal septum. Figure 17-1b The Olfactory Organs. Basal cell: divides to replace worn-out olfactory Olfactory gland receptor cells To olfactory bulb Cribriform plate Olfactory nerve fibers Lamina propria Developing olfactory receptor cell Olfactory receptor cell Olfactory epithelium Supporting cell Mucous layer Knob Substance being smelled b An olfactory receptor is a modified neuron © 2015 Pearson Education, Inc. with multiple cilia-shaped dendrites. Olfactory dendrites: surfaces contain receptor proteins (see Spotlight Figure 17–2) 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 © 2015 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 © 2015 Pearson Education, Inc. Figure 17-2 Olfaction and Gustation (Part 4 of 10). Stimulus Olfaction and gustation are special senses that give us vital information about our environment. Although the sensory information is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons. mV Action potentials Dendrites Specialized olfactory neuron Stimulus removed −70 mV Stimulus Threshold Generator potential 0 Time (msec) © 2015 Pearson Education, Inc. to CNS Figure 17-2 Olfaction and Gustation (Part 7 of 10). Olfactory reception occurs on the surface membranes of the olfactory dendrites. Odorants—dissolved chemicals that stimulate olfactory receptors—interact with receptors called odorant-binding proteins on the membrane surface. 1 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 MUCOUS LAYER 2 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 opens sodium ion channels in the plasma membrane, which then begins to depolarize. Closed sodium channel If sufficient depolarization occurs, an action potential is triggered in the axon, and the information is relayed to the CNS. + + + Depolarized membrane Receptor protein Inactive G protein RECEPTOR CELL 3 cAMP Active G protein adenylate ATP cyclase cAMP © 2015 Pearson Education, Inc. cAMP + + cAMP 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 © 2015 Pearson Education, Inc. 17-2 Taste (Gustation) • Taste Buds • Associated with epithelial projections (lingual papillae) on superior surface of tongue © 2015 Pearson Education, Inc. 17-2 Taste (Gustation) • Four Types of Lingual Papillae 1. Filiform papillae • Provide friction • Do not contain taste buds 2. Fungiform papillae • Contain about five taste buds each 3. Vallate papillae • Contain 100 taste buds each 4. Foliate papillae © 2015 Pearson Education, Inc. Figure 17-3a Gustatory Receptors. Water receptors (pharynx) Umami a Location of tongue papillae. © 2015 Pearson Education, Inc. 17-2 Taste (Gustation) • Gustatory Discrimination • Four primary taste sensations 1. 2. 3. 4. © 2015 Pearson Education, Inc. Sweet Salty Sour Bitter 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 © 2015 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 © 2015 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 © 2015 Pearson Education, Inc. 17-2 Taste (Gustation) • Taste Sensitivity • Exhibits significant individual differences • Some conditions are inherited • For example, phenylthiocarbamide (PTC) • 70 percent of Caucasians taste it but 30 percent do not • Number of taste buds • Begins declining rapidly at age 50 © 2015 Pearson Education, Inc. Figure 17-2 Olfaction and Gustation (Part 6 of 10). RECEPTOR CELL Stimulus +30 mV 0 Stimulus removed Stimulus Threshold −60 −70 Receptor cell −70 mV Depolarization Synapse at dendrite 0 Time (msec) Sensory neuron −70 mV AXON Stimulus mV +30 Action potentials Synaptic delay 0 −60 −70 Generator potential 0 © 2015 Pearson Education, Inc. Time (msec) to CNS Figure 17-2 Olfaction and Gustation (Part 10 of 10). Salt and Sour Channels Sweet, Bitter, and Umami Receptors The diffusion of sodium ions from salt solutions or hydrogen ions from acids or sour solutions into the receptor cell leads to depolarization. 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. + H+ + Na+ + + + Na+ ion leak channel Sweet, bitter, or umami Membrane receptor Resting plasma membrane Inactive G protein Depolarized membrane + Depolarization of membrane stimulates release of chemical neurotransmitters. © 2015 Pearson Education, Inc. Depolarized membrane Active G protein + + Active G protein Active 2nd messenger 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 © 2015 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 a Gross and superficial anatomy of the accessory structures © 2015 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 © 2015 Pearson Education, Inc. Figure 17-4b External Features and Accessory Structures of the Eye. Superior rectus muscle Tendon of superior oblique muscle Lacrimal gland ducts Lacrimal punctum Lacrimal gland Lacrimal caruncle Ocular conjunctiva Superior lacrimal canaliculus Lateral canthus Medial canthus Lower eyelid Inferior lacrimal canaliculus Orbital fat Lacrimal sac Inferior rectus muscle Nasolacrimal duct Inferior nasal concha Inferior oblique muscle b The organization of the lacrimal apparatus © 2015 Pearson Education, Inc. Opening of nasolacrimal duct Figure 17-5a The Sectional Anatomy of the Eye. Fornix Palpebral conjunctiva Eyelash Optic nerve Ocular conjunctiva Ora serrata Cornea Lens Pupil Iris Corneal limbus Fovea Retina Choroid Sclera a Sagittal section of left eye © 2015 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 Posterior cavity Inner layer (retina) Neural part Pigmented part b © 2015 Pearson Education, Inc. Horizontal section of right eye Figure 17-5c The Sectional Anatomy of the Eye. Visual axis Anterior cavity Posterior chamber Anterior chamber Cornea Edge of pupil Iris Ciliary zonule Nose Corneal limbus Lacrimal punctum Conjunctiva 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 Central artery and vein © 2015 Pearson Education, Inc. Orbital fat c Horizontal dissection of right eye 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 © 2015 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye. Visual axis Anterior cavity Posterior chamber Anterior chamber Cornea Edge of pupil Iris Ciliary zonule Nose Corneal limbus Lacrimal punctum Conjunctiva 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 Central artery and vein © 2015 Pearson Education, Inc. Orbital fat c Horizontal dissection of right eye 17-3 The Eye • The Vascular Layer • Iris • Contains papillary muscles • Change diameter of pupil © 2015 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 © 2015 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 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 © 2015 Pearson Education, Inc. Figure 17-5c The Sectional Anatomy of the Eye. Visual axis Anterior cavity Posterior chamber Anterior chamber Cornea Edge of pupil Iris Ciliary zonule Nose Corneal limbus Lacrimal punctum Conjunctiva 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 Central artery and vein © 2015 Pearson Education, Inc. Orbital fat c Horizontal dissection of right eye Figure 17-7a The Organization of the Retina (Part 1 of 2). Horizontal cell Cone Rod Pigmented part of retina Rods and cones Amacrine cell Bipolar cells Ganglion cells LIGHT a © 2015 Pearson Education, Inc. The cellular organization of the retina. The photoreceptors are closest to the choroid, rather than near the posterior cavity (vitreous chamber). Figure 17-7b The Organization of the Retina. Pigmented part of retina Neural part of retina Central retinal vein Optic disc Central retinal artery Sclera Optic nerve Choroid b The optic disc in diagrammatic sagittal section. © 2015 Pearson Education, Inc. Figure 17-7c The Organization of the Retina. Fovea Macula c © 2015 Pearson Education, Inc. 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. Figure 17-8 A Demonstration of the Presence of a Blind Spot. © 2015 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) • Reenters circulation • Intraocular Pressure • Fluid pressure in aqueous humor • Helps retain eye shape © 2015 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 Ciliary zonule Pigmented epithelium Conjunctiva Ciliary body Sclera Posterior cavity (vitreous chamber) Choroid Retina © 2015 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 © 2015 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 © 2015 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 a © 2015 Pearson Education, Inc. The closer the light source, the longer the focal distance b The rounder the lens, the shorter the focal distance c 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 © 2015 Pearson Education, Inc. Figure 17-11 Accommodation. a For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted b For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed © 2015 Pearson Education, Inc. Figure 17-11a Accommodation. a For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted © 2015 Pearson Education, Inc. Figure 17-11b Accommodation. b For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed © 2015 Pearson Education, Inc. 17-3 The Eye • Light Refraction of Lens • Image reversal • Visual acuity • Clarity of vision • “Normal” rating is 20/20 © 2015 Pearson Education, Inc. Figure 17-12a Image Formation. a © 2015 Pearson Education, Inc. Light from a point at the top of an object is focused on the lower retinal surface. Figure 17-12b Image Formation. b © 2015 Pearson Education, Inc. Light from a point at the bottom of an object is focused on the upper retinal surface. Figure 17-12c Image Formation. Optic nerve c © 2015 Pearson Education, Inc. Light rays projected from a vertical object show why the image arrives upside down. (Note that the image is also reversed.) Figure 17-12d Image Formation. Optic nerve d © 2015 Pearson Education, Inc. 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.) Figure 17-13 Refractive Problems (Part 1 of 5). The eye has a fixed focal distance and focuses by varying the shape of the lens. © 2015 Pearson Education, Inc. A camera lens has a fixed size and shape and focuses by varying the distance to the film. Figure 17-13 Refractive Problems (Part 2 of 5). Emmetropia (normal vision) © 2015 Pearson Education, Inc. Figure 17-13 Refractive Problems (Part 3 of 5). 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. Myopic people 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. Myopic corrected with a diverging, concave lens © 2015 Pearson Education, Inc. Diverging lens Figure 17-13 Refractive Problems (Part 4 of 5). 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 on 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 © 2015 Pearson Education, Inc. Converging lens Figure 17-13 Refractive Problems (Part 5 of 5). 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 recovered 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. © 2015 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 © 2015 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 © 2015 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 © 2015 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. The pigment epithelium absorbs photons that are not absorbed by visual pigments. It also phagocytizes old discs shed from the tip of the outer segment. In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Melanin granules Outer Segment The outer segment of a photoreceptor contains flattened membranous plates, or discs, that contain the visual pigments. Inner Segment Discs Connecting stalks Mitochondria The inner segment contains the photoreceptor’s major organelles and is responsible for all cell functions other than photoreception. It also releases neurotransmitters. Golgi apparatus Nuclei Cone Rods Each photoreceptor synapses with a bipolar cell. Bipolar cell LIGHT a Structure of rods and cones © 2015 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 b Structure of rhodospin molecule © 2015 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 © 2015 Pearson Education, Inc. Figure 17-15 Cone Types and Sensitivity to Color. Light absorption (percent of maximum) 100 Blue cones 75 Rods Red Green cones cones 50 25 0 W AV E L E N G T H ( n m ) 400 450 500 550 600 650 Violet Blue Green Yellow Orange © 2015 Pearson Education, Inc. 700 Red Figure 17-18 A Standard Test for Color Vision. © 2015 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 © 2015 Pearson Education, Inc. Figure 17-16 Photoreception (Part 5 of 8). 1 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 curved 11-cis form; on absorbing light it changes to the more linear 11-trans form. This change activates the opsin molecule. © 2015 Pearson Education, Inc. Figure 17-16 Photoreception (Part 6 of 8). 2 Opsin activates transducin, which in turn activates phosphodiesterase (PDE) Transducin is a G protein—a membranebound enzyme complex Na+ PDE Transducin Disc membrane In this case, opsin activates transducin, and transducin in turn activates phosphodiesterase (PDE). © 2015 Pearson Education, Inc. Figure 17-16 Photoreception (Part 7 of 8). 3 Cyclic GMP levels decline and gated sodium channels close Phosphodiesterase is an enzyme that breaks down cGMP. Na+ GMP cGMP The removal of cGMP from the gated sodium channels results in their inactivation. The rate of Na+ entry into the cytoplasm then decreases. © 2015 Pearson Education, Inc. Figure 17-16 Photoreception (Part 8 of 8). IN LIGHT ACTIVE STATE −70 mV 4 Dark current is reduced and rate of neurotransmitter release declines The reduction in the rate of Na+ entry reduces the dark current. At the same time, active transport continues to export Na+ from the cytoplasm. When the sodium channels close, the membrane potential drops toward –70 mV. As the plasma membrane hyperpolarizes, the rate of neurotransmitter release decreases. This decrease signals the adjacent bipolar cell that the photoreceptor has absorbed a photon. After absorbing a photon, retinal does not spontaneously revert to he 11-cis form. Instead, the entire rhodopsin molecule must be broken down into retinal and opsin, in a process called bleaching. It is then reassembled. © 2015 Pearson Education, Inc. Na+ 17-4 Visual Physiology • Recovery after Stimulation • Bleaching • Rhodopsin molecule breaks down into retinal and opsin • Night blindness • Results from deficiency of vitamin A © 2015 Pearson Education, Inc. 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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 © 2015 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 geniculates with visual cortex © 2015 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 © 2015 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 © 2015 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 (II) Optic chiasm Optic tract Lateral geniculate nucleus Diencephalon and brain stem Suprachiasmatic nucleus Projection fibers (optic radiation) Visual cortex of cerebral hemispheres Left cerebral hemisphere © 2015 Pearson Education, Inc. 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 © 2015 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 © 2015 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 (VII) Vestibulocochlear nerve (VIII) Bony labyrinth of internal ear Cochlea Tympanic cavity Auditory tube To nasopharynx External acoustic meatus © 2015 Pearson Education, Inc. Tympanic membrane Round window Vestibule 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 © 2015 Pearson Education, Inc. Figure 17-22a The Middle Ear. Auditory Ossicles Malleus Incus Stapes Temporal bone (petrous part) Oval window Stabilizing ligaments Muscles of the Middle Ear Branch of facial nerve VII (cut) Tensor tympani muscle External acoustic meatus Stapedius muscle Tympanic cavity (middle ear) Round window Auditory tube Tympanic membrane a © 2015 Pearson Education, Inc. The structures 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 b The tympanic membrane and auditory ossicles © 2015 Pearson Education, Inc. Figure 17-22c The Middle Ear. Incus Malleus Points of attachment to tympanic membrane Stapes Base of stapes c The isolated auditory ossicles © 2015 Pearson Education, Inc. Figure 17-23b The Internal Ear. KEY Membranous labyrinth Semicircular ducts Bony labyrinth Anterior Lateral Vestibule Posterior Cristae within ampullae Maculae Endolymphatic sac Semicircular canal Cochlea Utricle Saccule Vestibular duct Cochlear duct Tympanic duct Spiral organ b The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple. © 2015 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 © 2015 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 © 2015 Pearson Education, Inc. Figure 17-24a The Semicircular Ducts. Vestibular branch (N VIII) Semicircular ducts Anterior Cochlea Ampulla Posterior Endolymphatic sac Lateral Endolymphatic duct Utricle Maculae Saccule a An anterior view of the right semicircular ducts, the utricle, and the saccule, showing the locations of sensory receptors. © 2015 Pearson Education, Inc. Figure 17-24b The Semicircular Ducts. Ampulla filled with endolymph Cupula Hair cells Crista ampullaris Supporting cells Sensory nerve b A cross section through the ampulla of a semicircular duct. © 2015 Pearson Education, Inc. Figure 17-24c The Semicircular Ducts. Direction of duct rotation Direction of relative endolymph movement Direction of duct rotation Semicircular duct Cupula At rest c Endolymph movement along the length of the duct moves the cupula and stimulates the hair cells. © 2015 Pearson Education, Inc. Figure 17-24d The Semicircular Ducts. Displacement in this direction stimulates hair cell Displacement in this direction inhibits hair cell Gelatinous material Kinocilium Stereocilia Hair cell Sensory nerve ending Supporting cell d © 2015 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 © 2015 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 © 2015 Pearson Education, Inc. Figure 17-25ab The Saccule and Utricle. Endolymphatic sac Endolymphatic duct Utricle Saccule a The location of the maculae Otoliths Gelatinous layer forming otolithic membrane Hair cells Nerve fibers b The structure of an individual macula © 2015 Pearson Education, Inc. Figure 17-25c The Saccule and Utricle. 1 Head in normal, upright position Gravity 2 Head tilted posteriorly Receptor output increases c © 2015 Pearson Education, Inc. Gravity Otolith moves “downhill,” distorting hair cell processes A diagrammatic view of utricular macular function when the head is held normally 1 and then tilted back 2 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 © 2015 Pearson Education, Inc. Figure 17-26 Pathways for Equilibrium Sensations. To superior colliculus and relay to cerebral cortex Red nucleus N III Semicircular canals Vestibular ganglion N IV Vestibular branch Vestibular nucleus N VI To cerebellum Vestibule Cochlear branch N XI Vestibulocochlear nerve (VIII) Vestibulospinal tracts © 2015 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 © 2015 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 © 2015 Pearson Education, Inc. 17-5 The Ear • Hearing • Cochlear duct receptors • Provide sense of hearing © 2015 Pearson Education, Inc. Figure 17-27a The Cochlea. Round window Stapes at oval window Scala vestibuli Cochlear duct Scala tympani Semicircular canals KEY Cochlear branch Vestibular branch Vestibulocochlear nerve (VIII) a The structure of the cochlea © 2015 Pearson Education, Inc. 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 (VIII) b Diagrammatic and sectional views of the cochlear spiral © 2015 Pearson Education, Inc. 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 © 2015 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 © 2015 Pearson Education, Inc. Figure 17-28a The Spiral Organ. Bony cochlear wall Scala vestibuli Vestibular membrane Spiral ganglion Cochlear duct Tectorial membrane Basilar membrane Scala tympani Spiral organ a A three-dimensional section of the cochlea, showing the compartments, tectorial membrane, and spiral organ © 2015 Pearson Education, Inc. Cochlear branch of N VIII Figure 17-28b The Spiral Organ (Part 1 of 2). Tectorial membrane Outer hair cell Basilar membrane Inner hair cell Nerve fibers b Diagrammatic and sectional views of the receptor hair cell complex of the spiral organ © 2015 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 © 2015 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) © 2015 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 © 2015 Pearson Education, Inc. Figure 17-29a The Nature of Sound. Wavelength Tympanic membrane Tuning fork Air molecules a Sound waves (here, generated by a tuning fork) travel through the air as pressure waves. © 2015 Pearson Education, Inc. Sound energy arriving at tympanic membrane Figure 17-29b The Nature of Sound. 1 wavelength Amplitude Time (sec) b 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 carried by the wave is its amplitude. The greater the amplitude, the louder the sound. © 2015 Pearson Education, Inc. Figure 17-30 Sound and Hearing (Part 1 of 2). External acoustic meatus Malleus Incus Stapes Oval window 3 Movement of sound waves 2 1 Round window Tympanic membrane 1 Sound waves arrive at tympanic membrane. © 2015 Pearson Education, Inc. 3 2 Movement of the tympanic membrane causes displacement of the auditory ossicles Movement of the stapes at the oval window establishes pressure waves in the perilymph of the scala vestibuli. Figure 17-30 Sound and Hearing (Part 2 of 2). Cochlear branch of cranial nerve VIII 6 Scala vestibuli (contains perilymph) Vestibular membrane Cochlear duct (contains endolymph) Basilar membrane 4 Scala tympani (contains perilymph) 5 4 The pressure waves distort the basilar membrane on their way to the round window of the scala tympani. © 2015 Pearson Education, Inc. 6 5 Vibration of the basilar membrane causes hair cells to vibrate 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 © 2015 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 © 2015 Pearson Education, Inc. Figure 17-32 Pathways for Auditory Sensations (Part 1 of 2). 1 Stimulation of hair cells at a specific location along the basilar membrane activates sensory neurons. Cochlea Low-frequency sounds High-frequency sounds Vestibular branch 2 Sensory neurons carry the sound information in the cochlear branch of the vestibulocochlear nerve (VIII) to the cochlear nucleus on that side. © 2015 Pearson Education, Inc. KEY Vestibulocochlear nerve (VIII) 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 © 2015 Pearson Education, Inc. Table 17-1 Intensity of Representative Sounds. © 2015 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 © 2015 Pearson Education, Inc.
