17 The Special Senses PowerPoint Lecture Presentations prepared by Jason LaPres Lone Star College North Harris
An Introduction to the Special Senses Five Special Senses 1. Olfaction 2. Gustation 3. Vision 4. Equilibrium 5. Hearing
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
17-1 Smell (Olfaction) Layers of Olfactory Organs Olfactory epithelium contains: Olfactory receptors Supporting cells Basal (stem) cells
17-1 Smell (Olfaction) Layers of Olfactory Organs Lamina propria contains: Areolar tissue Blood vessels Nerves Olfactory glands
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 The olfactory organ on the left side of the nasal septum
Figure 17-1b The Olfactory Organs Basal cell: divides to replace worn-out olfactory receptor cells Olfactory gland To olfactory bulb Cribriform plate Lamina propria Olfactory epithelium Olfactory nerve fibers Developing olfactory receptor cell Olfactory receptor cell Supporting cell Subsance being smelled An olfactory receptor is a modified neuron with multiple cilia extending from its free surface. Mucous layer Knob Olfactory cilia: surfaces contain receptor proteins (see Spotlight Fig. 17 3)
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
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
Figure 17-2 Olfactory and Gustatory Receptors Olfaction and gustation are special senses that provide us with vital information about our environment. Although the sensory information provided is diverse and complex, each special sense originates at receptor cells that may be neurons or specialized receptor cells that communicate with sensory neurons. Stimulus Action removed potentials Stimulus Dendrites Specialized olfactory neuron Stimulus Threshold Generator potential to CNS
17-2 Taste (Gustation) Gustation Provides information about the foods and liquids consumed Taste Receptors (Gustatory Receptors) Are distributed on tongue and portions of pharynx and larynx Clustered into taste buds
17-2 Taste (Gustation) Taste Buds Associated with epithelial projections (lingual papillae) on superior surface of tongue
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
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 Then on to thalamus and primary sensory cortex
Figure 17-3a Gustatory Receptors Water receptors (pharynx) Umami Sour Bitter Salty Sweet Landmarks and receptors on the tongue
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.
Figure 17-3c Gustatory Receptors Taste buds Taste buds LM 280 Nucleus of transitional cell Nucleus of gustatory cell Nucleus of basal cell Taste bud LM 650 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.
17-2 Taste (Gustation) Gustatory Discrimination Four primary taste sensations 1. Sweet 2. Salty 3. Sour 4. 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
17-2 Taste (Gustation) End Result of Taste Receptor Stimulation Release of neurotransmitters by receptor cell Neurotransmitters generate action potentials in afferent fiber
17-2 Taste (Gustation) Taste Sensitivity Exhibits significant individual differences Some conditions are inherited Number of taste buds Begins declining rapidly by age 50
Figure 17-2 Olfactory and Gustatory Receptors Receptor cell Stimulus Stimulus Stimulus removed Receptor depolarization Threshold Receptor cell Synapse Axon of sensory neuron Axon Stimulus Action potentials Synaptic delay Generator potential to CNS
Figure 17-2 Olfactory and Gustatory Receptors Salt and Sour Receptors Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell. Sweet, Bitter, and Umami Receptors Receptors responding to stimuli that produce sweet, bitter, and umami sensations are linked to G proteins called gustducins (GUST-doos- inz) protein complexes that use second messengers to produce their effects. 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 Inactive 2nd messenger Depolarization of membrane stimulates release of chemical neurotransmitters. 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
17-3 Accessory Structures of the Eye Eyelids (Palpebrae) Continuation of skin Blinking keeps surface of eye lubricated, free of dust and debris
17-3 Accessory Structures of the Eye Conjunctiva Epithelium covering inner surfaces of eyelids (and outer surface of eye
Figure 17-4b External Features and Accessory Structures of the Eye Superior Tendon of superior rectus muscle oblique muscle Lacrimal gland ducts Lacrimal gland Ocular conjunctiva Lateral canthus Lower eyelid Orbital fat Inferior rectus muscle Inferior oblique muscle The organization of the lacrimal apparatus. Lacrimal punctum Lacrimal caruncle Superior lacrimal canaliculus Medial canthus Inferior lacrimal canaliculus Lacrimal sac Nasolacrimal duct Inferior nasal concha Opening of nasolacrimal duct
17-3 The Eye Three Layers of the Eye 1. Outer fibrous layer 2. Intermediate vascular layer 3. Deep inner layer
17-3 The Eye Eyeball Is hollow Is divided into two cavities 1. Large posterior cavity 2. Smaller anterior cavity
Figure 17-5a The Sectional Anatomy of the Eye Optic nerve Fornix Palpebral conjunctiva Eyelash Ocular conjunctiva Ora serrata Cornea Lens Pupil Iris Fovea Limbus Retina Choroid Sclera Sagittal section of left eye
Figure 17-5b The Sectional Anatomy of the Eye Fibrous layer Neural layer (retina) Cornea Sclera Neural part Pigmented part Anterior cavity Posterior cavity Vascular layer (uvea) Iris Ciliary body Choroid Horizontal section of right eye
Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Nose Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Ciliary processes Lens Lateral canthus Ciliary body Ora serrata Sclera Choroid Retina Ethmoidal labyrinth Posterior cavity Medial rectus muscle Lateral rectus muscle Optic disc Fovea Optic nerve Central artery and vein Horizontal dissection of right eye Orbital fat
17-3 The Eye The Fibrous Layer Sclera (white of the eye) Cornea
17-3 The Eye Vascular Layer 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
Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Nose Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Ciliary processes Lens Lateral canthus Ciliary body Ora serrata Sclera Choroid Retina Ethmoidal labyrinth Posterior cavity Medial rectus muscle Lateral rectus muscle Optic disc Fovea Optic nerve Central artery and vein Horizontal dissection of right eye Orbital fat
17-3 The Eye The Vascular Layer Iris Contains papillary muscles Change diameter of pupil
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) The pupillary constrictor muscles form a series of concentric circles around the pupil. When these sphincter muscles contract, the diameter of the pupil decreases. Decreased light intensity Increased sympathetic stimulation Increased light intensity Increased parasympathetic stimulation
17-3 The Eye The Vascular Layer Ciliary Body Contains ciliary processes, and ciliary muscle that attaches to suspensory ligaments of lens
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
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
Figure 17-5c The Sectional Anatomy of the Eye Visual axis Anterior cavity Cornea Nose Posterior chamber Anterior chamber Edge of pupil Iris Suspensory ligament of lens Corneal limbus Lacrimal punctum Conjunctiva Lacrimal caruncle Lower eyelid Medial canthus Ciliary processes Lens Lateral canthus Ciliary body Ora serrata Sclera Choroid Retina Ethmoidal labyrinth Posterior cavity Medial rectus muscle Lateral rectus muscle Optic disc Fovea Optic nerve Central artery and vein Horizontal dissection of right eye Orbital fat
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).
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).
Figure 17-7b The Organization of the Retina Pigmented part of retina Neural part of retina Central retinal vein Central retinal artery Optic disc Sclera Optic nerve Choroid The optic disc in diagrammatic sagittal section.
Figure 17-7c The Organization of the Retina Fovea Optic disc (blind spot) Macula Central retinal artery and vein emerging from center of optic disc A photograph of the retina as seen through the pupil.
17-3 The Eye Inner Neural Part Bipolar cells Neurons of rods and cones synapse with ganglion cells
17-3 The Eye Optic Disc Circular region just medial to fovea Origin of optic nerve Blind spot
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
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
Figure 17-9 The Circulation of Aqueous Humor Cornea Anterior cavity Pupil Anterior chamber Posterior chamber Scleral venous sinus Ciliary process Suspensory ligaments Pigmented epithelium Lens Posterior cavity (vitreous chamber) Body of iris Conjunctiva Ciliary body Sclera Choroid Retina
17-3 The Eye Large Posterior Cavity (Vitreous Chamber) Vitreous body Gelatinous mass Helps stabilize eye shape and supports retina
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
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
Figure 17-10 Factors Affecting Focal Distance Focal distance Focal distance Focal distance Light from distant source (object) Close source Lens Focal point The closer the light source, the longer the focal distance 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
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
Figure 17-11a Accommodation For Close Vision: Ciliary Muscle Contracted, Lens Rounded Lens rounded Focal point on fovea Ciliary muscle contracted
Figure 17-11b Accommodation For Distant Vision: Ciliary Muscle Relaxed, Lens Flattened Lens flattened Ciliary muscle relaxed
Figure 17-12a Image Formation Light from a point at the top of an object is focused on the lower retinal surface.
Figure 17-12b Image Formation Light from a point at the bottom of an object is focused on the upper retinal surface.
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.)
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.)
Figure 17-13 Accommodation Problems The eye has a fixed focal length and focuses by varying the shape of the lens. A camera lens has a fixed size and shape and focuses by varying the distance to the film.
Figure 17-13 Accommodation Problems Emmetropia (normal vision)
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
Figure 17-13 Accommodation Problems Hyperopia (farsightedness) If the eyeball is too shallow or the lens is too flat, hyperopia results. The ciliary muscle must contract to focus even a distant object o the retina. And at close range the lens cannot provide enough refraction to focus an image on the retina. Older people become farsighted as their lenses lose elasticity, a form of hyperopia called presbyopia (presbys, old man). Hyperopia corrected with a converging, convex lens Converging lens
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.
17-4 Visual Physiology Visual Physiology Rods Respond to almost any photon, regardless of energy content Cones Have characteristic ranges of sensitivity
17-4 Visual Physiology Anatomy of Rods and Cones Outer segment with membranous discs Inner segment Narrow stalk connects outer segment to inner segment
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
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. Melanin granules Outer Segment In a rod, each disc is an independent entity, and the outer segment forms an elongated cylinder. Discs Inner Segment Connecting stalks Mitochondria Golgi apparatus Nuclei Cone Rods Each photoreceptor synapses with a bipolar cell. Bipolar cell Structure of rods and cones. LIGHT
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. Retinal Rhodopsin molecule Opsin Structure of rhodospin molecule.
17-4 Visual Physiology Color Vision Integration of information from red, green, and blue cones Color blindness Inability to detect certain colors
Figure 17-15 Cone Types and Sensitivity to Color Light absorption (percent of maximum) Blue cones Rods Green cones Red cones W A V E L E N G T H (nm) Violet Blue Green Yellow Orange Red
Figure 17-16 A Standard Test for Color Vision
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
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.
Figure 17-17 Photoreception Opsin activates transducin, which in turn activates phosphodiestease (PDE) Transducin is a G protein a membrane-bound enzyme complex PDE Transducin Disc membrane 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 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
17-4 Visual Physiology Recovery after Stimulation Bleaching Rhodopsin molecule breaks down into retinal and opsin Night blindness Results from deficiency of vitamin A
Figure 17-18 Bleaching and Regeneration of Visual Pigments 11-cis retinal and opsin are reassembled to form rhodopsin. Photon On absorbing light, retinal changes to a more linear shape. This change activates the opsin molecule. 11-trans retinal Opsin activation changes the Na permeability of the outer segment, and this changes the rate of neurotransmitter release by the inner segment at its synapse with a bipolar cell. Na Na 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. Opsin ADP 11-cis retinal enzyme The retinal is converted to its original shape. This conversion requires energy in the form of ATP. ATP 11-trans retinal Opsin After absorbing a photon, the rhodopsin molecule begins to break down into retinal and opsin, a process known as bleaching. 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. Neurotransmitter release Bipolar cell Ganglion cell
Figure 17-20 The Visual Pathways Combined Visual Field Left side Right side Left eye only 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 Projection fibers (optic radiation) Diencephalon and brain stem Suprachiasmatic nucleus Visual cortex of cerebral hemispheres Superior colliculus Left cerebral hemisphere Right cerebral hemisphere
17-5 The Ear The External Ear Auricle Surrounds entrance to external acoustic meatus Protects opening of canal Provides directional sensitivity
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
Figure 17-21 The Anatomy of the Ear External Ear Middle Ear Internal Ear Elastic cartilages Auditory ossicles Auricle Oval window Semicircular canals Petrous part of temporal bone Facial nerve (N VII) Vestibulocochlear nerve (N VIII) Bony labyrinth of internal ear Tympanic cavity Cochlea To nasopharynx Auditory tube External acoustic meatus Tympanic membrane Round window Vestibule
17-5 The Ear The External Ear Secrete waxy material Keeps foreign objects out of tympanic membrane Slows growth of microorganisms in external acoustic meatus
17-5 The Ear The Middle Ear 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)
Figure 17-22a The Middle Ear Auditory Ossicles Malleus Incus Stapes Temporal bone (petrous part) Stabilizing ligaments Branch of facial nerve VII (cut) External acoustic meatus Tympanic cavity (middle ear) Tympanic membrane Oval window Muscles of the Middle Ear Tensor tympani muscle Stapedius muscle Round window Auditory tube The structures of the middle ear.
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
17-5 The Ear The Internal Ear Contains fluid called endolymph Bony labyrinth surrounds and protects membranous labyrinth Subdivided into: Vestibule Semicircular canals Cochlea
Figure 17-23b The Internal Ear Semicircular ducts Anterior Lateral Posterior Vestibule KEY Cristae within ampullae Maculae Endolymphatic sac Membranous labyrinth Bony labyrinth Semicircular canal Cochlea Utricle Saccule Vestibular duct Cochlear duct Tympanic duct Spiral organ The bony and membranous labyrinths. Areas of the membranous labyrinth containing sensory receptors (cristae, maculae, and spiral organ) are shown in purple.
Figure 17-23a The Internal Ear Perilymph Bony labyrinth Endolymph Membranous labyrinth KEY Membranous labyrinth Bony 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.
17-5 The Ear The Internal Ear Vestibule Receptors provide sensations of gravity and linear acceleration Semicircular canals Contain semicircular ducts Receptors stimulated by rotation of head
17-5 The Ear The Internal Ear Cochlea Contains cochlear duct (elongated portion of membranous labyrinth) Receptors provide sense of hearing
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
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
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
17-5 The Ear The Semicircular Ducts Each duct contains: Ampulla with gelatinous cupula Associated sensory receptors Stereocilia resemble long microvilli Are on surface of hair cell Kinocilium single large cilium
Figure 17-24a The Semicircular Ducts Semicircular ducts Anterior Posterior Lateral Ampulla Vestibular branch (N VIII) Cochlea 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
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
Figure 17-24c The Semicircular Ducts Direction of duct rotation 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.
Figure 17-24d The Semicircular Ducts Displacement in this direction stimulates hair cell Displacement in this direction inhibits hair cell Kinocilium Stereocilia Hair cell Sensory nerve ending Supporting cell 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 Statoconia Densely packed calcium carbonate crystals on surface of gelatinous mass Otolith (ear stone) = gelatinous matrix and statoconia
Figure 17-25ab The Saccule and Utricle The location of the maculae Gelatinous material Statoconia Otolith Hair cells Nerve fibers The structure of an individual macula
Figure 17-25c The Saccule and Utricle Head in normal, upright position Gravity Head tilted posteriorly Gravity Receptor output increases 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
Figure 17-26 Pathways for Equilibrium Sensations To superior colliculus and relay to cerebral cortex Vestibular ganglion Red nucleus N III N IV Semicircular canals Vestibular branch N VI Vestibular nucleus Vestibule To cerebellum Cochlear branch N XI Vestibulocochlear nerve (N VIII) Vestibulospinal tracts
17-5 The Ear Hearing Cochlear duct receptors Provide sense of hearing
Figure 17-27a The Cochlea Round window Stapes at oval window Scala vestibuli Cochlear duct Scala tympani Semicircular canals Cochlear branch Vestibular branch KEY Vestibulocochlear nerve (N VIII) The structure of the cochlea 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 Tectorial membrane Basilar membrane From oval window Scala vestibuli (contains perilymph) Cochlear duct (contains endolymph) Spiral organ Spiral ganglion To round window Scala tympani (contains perilymph) Cochlear nerve Vestibulocochlear nerve (N VIII) Diagrammatic and sectional views of the cochlear spiral
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
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 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
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
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)
17-5 The Ear Pressure Wave Pitch Our sensory response to frequency Amplitude Intensity of sound wave Sound energy is reported in decibels
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.
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.
Figure 17-30 Sound and Hearing External acoustic meatus Malleus Incus Stapes Oval window Movement of sound waves Tympanic membrane Round window Sound waves arrive at tympanic membrane. 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 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. 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.
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. 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. Motor output to spinal cord through the tectospinal tracts KEY Primary pathway Secondary pathway Motor output
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