Chapter 15: Special Senses Lecture Outline (PDF)

Chapter 15 Lecture Outline Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written...

Chapter 15 Lecture Outline Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education. See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes and animations. 15-1 Copyright © McGraw-Hill Education. Permission required for reproduction or display.  Special Senses Olfaction Taste Visual system Hearing and balance 15-2  15.1 Olfaction Seven primary odors now recognized, but average person can recognize 4000 different odors. Perceived by olfactory epithelium Cilia (olfactory hairs) of olfactory neuron embedded in mucus. Odorants dissolve in mucus. Somehow (mechanism unknown) odorants attach to receptors, cilia depolarize and initiate action potentials in olfactory neurons. One receptor may respond to more than one type of odor. Olfactory epithelium is replaced as it wears down. Olfactory neurons are replaced by basal cells every two months. 15-3 Olfaction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Frontal bone Olfactory bulb Olfactory tract Fibers of olfactory nerve Cribiform plate of ethmoid bone Cut edge of Olfactory region epithelium Nasal cavity Nasopharynx Hard palate (a) Medial view Secondary Granule cell neurons Tufted cell of olfactory Mitral cell bulb Olfactory Olfactory bulb tract Cribriform Foramen Posterior plate Olfactory nerve Anterior Connective processes tissue Axon Basal cell Supporting cell Olfactory epithelium Olfactory neuron Dendrite Mucous layer on epithelial Cilia (olfactory hairs) surface Olfactory vesicle Medial view (b)  Neuronal Pathways of Olfaction Olfactory sensory pathway: olfactory neurons (bipolar) in the olfactory epithelium pass through cribiform plate to olfactory bulbs and synapse with tufted cells or mitral cells. These extend to the olfactory tracts. Information goes to olfactory Secondary Granule cell neurons cortex of the frontal lobe of olfactory bulb Tufted cell Mitral cell without going through thalamus Olfactory Olfactory bulb (only major sense that does not tract go through thalamus). Cribriform Foramen plate Posterior Olfactory nerve Anterior The frontal lobe affects processes Connective tissue Axon Basal cell conscious perception of smell Supporting cell and interacts with limbic system. Olfactory epithelium Olfactory neuron Dendrite Mucous layer on epithelial Cilia (olfactory hairs) surface Olfactory vesicle Medial view 15-5  Olfactory Neuronal Pathways and Cortex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Intermediate olfactory 1 Processes of the olfactory nerves, formed by the area axons of the olfactory neurons, project through the Medial olfactory area foramina in the cribriform plate to the olfactory bulb. Frontal bone 2 Axons of neurons in the olfactory bulb project 5 Olfactory tract through the olfactory tract to the olfactory cortex or secondary olfactory areas. 4 Olfactory bulb 3 The olfactory cortex is involved in the 2 conscious perception of smell. Fibers of olfactory nerve 6 4 The medial olfactory area is involved in the 1 Nasal bone visceral and emotional reaction to odors. 3 Nasal cavity Olfactory cortex 5 The intermediate olfactory area receives input from the medial olfactory area and olfactory cortex. 6 Axons from the intermediate olfactory area project along the olfactory tract to the olfactory bulb. Action potentials carried by those axons modulate the activity of the neurons in the olfactory bulb. Medial view 15-6  15.2 Taste Papillae = bumps on tongue – Taste bud = supporting cells surrounding taste (gustatory) cells. On the sides of the papillae. – Taste cells have microvilli (gustatory hairs) extending into taste pores – Replaced about every 10 days – Is closely associated with smell. 15-7  Taste Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nerve fiber of Basal cell sensory neuron Supporting Taste cell bud Taste cell Taste hair Taste pore Epithelium (a) Foliate papilla (b) Taste bud Taste hair Synaptic vesicles Nucleus Sensory neuron terminal 15-8 (c) Taste cell  Taste Types Sour. Most sensitive receptors on lateral aspects of the tongue. Salty. Most sensitive receptors on tip of tongue. Shares lowest sensitivity with sweet. Anything with Na+ causes depolarization plus other metal ions. Craved by humans. Bitter. Most sensitive receptors on posterior aspect. Highest sensitivity. Sensation produced by alkaloids, which are toxic. Sweet. Most sensitive receptors on tip of tongue. Shares lowest sensitivity with salty. Sugars, some carbohydrates, and some proteins (NutraSweet: aspartame). Craved by humans. Umami (Glutamate). Scattered sensitivity. Caused by amino acids. Craved by humans. 15-9  Taste Texture affects the perception of taste Temperature affects taste perception Very rapid adaptation, both at level of taste bud and within the CNS Taste influenced by olfaction Different tastes have different thresholds with bitter being the taste to which we are most sensitive. Many alkaloids (bitter) are poisonous. 15-10 Neuronal Pathways for Taste Chorda tympani (part of VII): carry sensations from anterior one-third of tongue (except from circumvallate papillae Cranial nerve IX and X carry information from posterior one-third tongue, circumvallate papillae, superior pharynx, epiglottis. Information goes to medulla oblongata where decussation takes place and information projects from there to the thalamus. Then projects to taste area of cortex (extreme inferior end of the postcentral gyrus) 15-11  Neuronal Pathways for Taste Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Taste area of cortex 1 Axons of sensory neurons, which synapse with taste receptors, pass 4 through cranial nerves VII, IX, and X and through the ganglion of Thalamus each nerve (enlarged portion of each nerve). 2 The axons enter the brainstem 3 and synapse in the nucleus of Nucleus of the tractus solitarius. tractus V solitarius 3 Axons from the nucleus of the tractus solitarius synapse in the Chorda tympani thalamus. VII IX 4 Axons from the thalamus 2 X terminate in the taste area of 1 the cortex. Foramen magnum Facial nerve (VII) Trigeminal nerve (V) (lingual branch) Glossopharyngeal nerve (IX) Vagus nerve (X) 15-12  15.3 Visual System Eyebrows: shade; inhibit sweat Eyelids (palpebrae) with conjunctiva. – Palpebral fissure: space between eyelids. – Canthi: lateral and medial, eyelids meet. – Medial canthus has caruncle with modified sweat and sebaceous glands – Five layers of tissues including a dense connective tissue tarsal plate that helps maintain shape of lid Eyelashes: double/triple row of hairs Ciliary glands (modified sweat glands) empty into hair follicles. Meibomian glands at inner margins produce sebum. Conjunctiva: thin transparent mucous membrane – Palpebral conjunctiva: inner surface eyelids – Bulbar conjunctiva: anterior surface of eye except over pupil 15-13  Visual System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Superior palpebra Eyebrow (eyelid) Iris Pupil Sclera Caruncle Lateral canthus Inferior Medial palpebra canthus (eyelid) © The McGraw-Hill Higher Education, Inc./Eric Wise, photographer  Sagittal Section Through Eye Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Levator palpebrae Eyebrow superioris muscle Orbicularis oculi muscle Smooth muscle to tarsal plate Superior conjunctival fornix Superior rectus muscle Bulbar conjunctiva Palpebral conjunctiva Tarsal (meibomian) gland Tarsal plate Cornea Eyelash Palpebral fissure Skin Areolar connective tissue Inferior rectus Orbicularis oculi muscle Lower muscle eyelid Inferior oblique Tarsal plate (inferior muscle palpebra) Palpebral conjunctiva Inferior conjunctival fornix 15-15 Sagittal section  Lacrimal Apparatus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Puncta Lacrimal 1 Tears are produced in the gland 1 lacrimal gland and exit the gland rough several lacrimal ducts. Lacrimal 2 The tears pass over the canaliculi surface of the eye. Lacrimal 2 ducts 3 Tears enter the lacrimal Lacrimal 3 canaliculi. sac 4 Tears are carried through the 4 lacrimal sac to the nasolacrimal duct. 5 Tears enter the nasal cavity Nasolacrimal from the nasolacrimal duct. duct 5 15-16 Extrinsic Eye Muscles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Posterior View Optic nerve Levator palpebrae superioris (cut) Lateral rectus Medial rectus Superior rectus Superior oblique Trochlea (a) Superior view Anterior View Superior Trochlea Levator palpebrae superioris (cut) Superior oblique Optic nerve Superior rectus Lateral rectus Inferior rectus Inferior oblique (b) Lateral view Inferior 15-17  Anatomy of the Eye Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Superior rectus muscle (cut) Eyeball Medial rectus muscle Lateral rectus muscle Optic nerve Optic chiasm Superior view © The McGraw-Hill Higher Education, Inc./Rebecca Gray, photographer/Don Kincaid, dissections Three tunics: Fibrous: sclera and cornea Vascular: choroid, ciliary body, iris Nervous: retina 15-18  The Eye Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vitreous chamber (filled with vitreous humor) Both filled with aqueous Central retinal humor Conjunctiva artery and vein Cornea (fibrous tunic) Anterior chamber Posterior chamber Optic nerve Iris (vascular tunic) Pupil Vitreous Lens humor Retina Suspensory (nervous tunic) ligaments Choroid Ciliary body (vascular tunic) (vascular tunic) Sclera (fibrous tunic) Anatomy of the Eye: Fibrous Tunic Sclera: white outer layer. Maintains shape, protects internal structures, provides muscle attachment point, continuous with cornea. Dense collagenous connective tissue with elastic fibers. Collagen fibers are large and opaque. Cornea: connective tissue matrix containing collagen, elastic fibers and proteoglycans. Layer of stratified squamous epithelium on the outer surface. Collagen fibers are small, thus transparent. More proteoglycans than sclera, low water content (water would scatter light). Avascular, transparent, allows light to enter eye; bends and refracts light. 15-20  Anatomy of the Eye: Vascular Tunic Middle layer. Contains most of the blood vessels of the eye: branches off the internal carotid arteries. Contains melanin. – Iris: colored part of the eye. Controls light entering the pupil. Smooth muscle determines size of pupil. Sphincter pupillae: parasympathetic Dilator pupillae: sympathetic – Ciliary body: produces aqueous humor that fills anterior chamber Ciliary muscles: control lens shape; smooth muscle. Ciliary processes attached to suspensory ligaments of lens – Choroid: associated with sclera. Very thin, pigmented. 15-21  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sclera Choroid Vascular Retina Tunic Conjunctiva Ciliary muscle Scleral venous sinus Ciliary body Ciliary ring (canal of Schlemm) Iris Ciliary processes Posterior Suspensory chamber ligaments Anterior Vitreous chamber chamber Capsule of Cornea the lens Outer Lens epithelium Inner epithelium (a) Pupil Ciliary Sphincter Dilator ring Ciliary pupillae pupillae Ciliary body processes Lens Suspensory (c) (d) ligaments (b)  Anatomy of the Eye: Retina Two layers – Pigmented retina: outer, pigmented layer; pigmented simple cuboidal epithelium. Pigment of this layer and choroid help to separate sensory cells and reduce light scattering. – Sensory retina: inner layer of rod and cone cells sensitive to light. 15-23  Opthalmoscopic View of Retina Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lens focuses light on macula lutea and fovea centralis Macula – Macula lutea: small Optic Fovea yellow spot disc centralis – Fovea centralis: area Retinal of greatest visual vessels acuity; photoreceptor cells tightly packed Optic disc: blind spot. Area through which blood (a) vessels enter eye, where nerve processes from sensory retina meet and exit from eye (b) 15-24 a: © A. L. Blum/Visuals Unlimited 15-25 15-26  Chambers of the Eye Anterior compartment: anterior to lens; filled with aqueous humor – Anterior chamber: between cornea and iris – Posterior chamber: between iris and lens – Helps maintain intraocular pressure; supplies nutrients to structures bathed by it; contributes to refraction of light Produced by ciliary process; returned to venous circulation through canal of Schlemm or scleral venous sinus Glaucoma: abnormal increase in intraocular pressure Vitreous chamber: posterior to lens. Filled with jelly-like vitreous humor. Helps maintain intraocular pressure, holds lens and retina in place, refracts light. 15-27  The Eye Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Vitreous chamber (filled with vitreous humor) Both filled with aqueous Central retinal humor Conjunctiva artery and vein Cornea (fibrous tunic) Anterior chamber Posterior chamber Optic nerve Iris (vascular tunic) Pupil Vitreous Lens humor Retina Suspensory (nervous tunic) ligaments Choroid Ciliary body (vascular tunic) (vascular tunic) Sclera (fibrous tunic)  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sclera Choroid Retina Chambers Conjunctiva Ciliary muscle Scleral venous sinus Ciliary body Ciliary ring (canal of Schlemm) Iris Ciliary processes Posterior Suspensory chamber ligaments Anterior Vitreous chamber chamber Capsule of Cornea the lens Outer Lens epithelium Inner epithelium (a) Pupil Ciliary Sphincter Dilator ring Ciliary pupillae pupillae Ciliary body processes Lens Suspensory (c) (d) ligaments (b)  Lens Held by suspensory ligaments attached to ciliary muscles. Changes shape as ciliary muscles contract and relax. Made of long columnar epithelial cells that enucleate and produce proteins called crystallines. Surrounded by a highly elastic, transparent capsule Transparent, biconvex 15-30  Light Visible light: portion of electromagnetic spectrum detected by human eye Refraction: bending of light Convergence: light striking a convex surface Focal point: point where light rays converge and cross Focusing: causing light to converge Lens changes shape causing adjustment of focal point on the retina 15-31 Electromagnetic Spectrum Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Increasing energy Increasing wavelength 0.001 nm 1 nm 10 nm 1000 nm 0.01 cm 1 cm 1m 100 m UV Gamma rays X- rays light Infrared Microwaves Radio waves cm = 102 m mm = 103 m nm = 109 m Visible light 380 nm 430 nm 500 nm 560 nm 600 nm 650 nm 750 nm 15-32  Focusing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Distant vision Ciliary muscles in the ciliary body are relaxed. Emmetropia: Tension in suspensory ligaments is high. normal resting FP condition of lens. Ciliary muscle is Lens flattened relaxed. Lens is flat. (a) Near vision Far point of Ciliary muscles in the ciliary body contract, moving vision: point at ciliary body t oward lens. which lens does Tension in suspensory ligaments is low. not have to A thicken to focus. A FP 20 feet or more Lens thickened from eye. 15-33 (b)  Near Point of Vision Closer than 20 feet. Changes occur in lens, size of pupil, and distance between pupils – Accommodation: ciliary muscles contract due to parasympathetic input via cranial nerve III. Pulls choroid toward lens reducing tension on suspensory ligaments. Lens becomes more spherical, greater refraction of light – Pupil constriction: varies depth of focus – Convergence: as objects move close to the eye, eyes are rotated medially. Reflex contraction of the medial rectus muscles 15-34  Structure and Function of the Retina Sensory retina: three layers of neurons: photoreceptor, bipolar, and ganglionic – Cell bodies form nuclear layers separated by plexiform layers, where neurons of adjacent layers synapse with each other Pigmented retina: single layer of cells; filled with melanin. With choroid, enhances visual acuity by isolating individual photoreceptors, reducing light scattering 15-35  Rods and Cones Photoreceptive End Photoreceptive Molecule Function Location Rod Cylindrical Rhodopsin Noncolor vision; vision under Over most of retina; none in conditions of low light fovea centralis Cones Conical Iodopsin Color vision; visual acuity Numerous in fovea centralis and macula; sparse over rest of retina 15-36  Retina Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Choroid Pigmented Pigment layer cell Direction of action Photoreceptor potential Rod Cone cell layer propagation Rod cell Horizontal Cone Outer plexiform cell Neural layer layer Bipolar Bipolar layer cell Amacrine cell Inner plexiform layer Interplexiform Ganglionic cell Ganglion cell Direction layer (b) of light Nerve fibers to optic nerve (a) Optic nerve b: © Steve Gschmeissner/ Photo Researchers, Inc. 15-37  Rods Bipolar photoreceptor cells; black and white vision. Found over most of retina, but not in fovea. More sensitive to light than cones. – Protein rhodopsin changes shape when struck by light; and eventually separates into its two components: opsin and retinal – Retinal can be converted to Vitamin A from which it was originally derived. In absence of light, opsin and retinal recombine to form rhodopsin. – Rods are unusual sensory cells: when not stimulated they are depolarized. Light causes them to hyperpolarize. – Depolarization of rods causes depolarization of bipolar cells causing depolarization of ganglion cells – Light and dark adaptation: adjustment of eyes to changes in light. Happens because of changes in amount of available rhodopsin. 15-38  Photoreceptors Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Disc Disc Outer membrane Outer segment Folding of outer membrane to form discs Inner Disc segment (c) Outside Extracellular of disc plug Nuclei membrane Opsin Rhodopsin Retinal Gated Na+ channel Disc Axons membrane Synaptic    ending Rod cGMP (a) G protein cGMP Inside (transducin) phosphodiesterase (b) Cone (d) of disc membrane 15-39  Rod Cell Hyperpolarization Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Lightpulse 1 Rod cell is unstimulated in dark conditions. – 25 Rhodopsin and the G protein, transducin, are both (mV) inactive, and gated Na+ channels with attached – 30 Hyperpolarization cGMP are open, allowing Na+ to enter the cell. – 35 1 2 3 Rhodopsin Time(s) 2 Glutamate is constantly released from the Open gated Na+ channel Rod cell (dark configuration) (unstimulated) 2 Glutamate is cGMP (dark configuration) unstimulated rod cell. phosphodiesterase continuously Na+ released. 1 3 Glutamate inhibits bipolar cells from releasing neurotransmitters that stimulate ganglionic cells. 3 Bipolar cell  βα inhibited cGMP Inactive transducin (Gprotein) (a) Dark Light pulse 1 Exposure to light stimulates the rod cell. Rhodopsin – 25 and the attached transducing are also activated. (mV) Transducin activates cGMP phosphodiesterase, which – 30 catalyzes the conversion of cGMP to GMP, closing Na + Hyperpolarization – 35 channels. The rod cell is hyperpolarized when Na + no 21 3 Rodcell Time (s) longer enters the cell. (hyperpolarized) 2 Glutamate Closed gated Na+ channel release Rhodopsin (light configuration) 2 Glutamate release from rod cell decreases. decreases. (light configuration) Na+ 3 1 Bipolarcell nolonger inhibited 3 Bipolar cells release neurotransmitters that stimulate β α ganglionic cells to generate action potentials. GMP cGMP Transducin Neurotransmitters active (b) Light released 15-40  Light and Dark Adaptation: Rods: in bright light, more rhodopsin broken down into Vitamin A, protecting the eye and making it less sensitive to light. In darker conditions, more rhodopsin produced so eye is more sensitive to light. Takes eyes a while to accommodate when going from dark to light and vice versa because of these chemical changes that must occur. Pupils: constriction in bright light; dilation in dim light. 15-41  Cones Bipolar receptor cells. Responsible for color vision and Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. visual acuity. 100 – Numerous in fovea and 90 macula lutea; fewer over 80 Red pigment (Ser180) rest of retina. 70 – As light intensity decreases (percent of maximum) Relative absorption 60 Red pigment so does our ability to see 50 (Ala180) color. 40 – Visual pigment is iodopsin: 30 Green pigment three types that respond to 20 blue, red and green light 10 Blue pigment (cyanolabe, erythrolabe, 0 chlorolabe) – Overlap in response to light, thus interpretations of gradation of color possible: 400 450 500 550 600 Wavelength (nanometers) 650 several millions 15-42 Inner Layers of the Retina Rods and cones synapse with bipolar cells that synapse with ganglion cells in all areas except the fovea. Except in fovea centralis, ganglion cell axons converge at optic disc, then exit via optic nerve then impulses travel to visual cortex Fovea centralis: highest visual acuity Rods: spatial summation. One bipolar cell receives input from numerous rods, one ganglion cell receives input from several bipolar cells. Cones exhibit little or no convergence. 15-43  Receptive Fields Area from which a ganglion cell receives input Roughly circular with receptive field center Those in fovea centralis smaller than in other parts of retina Two types of receptive fields – On-center ganglion cells: generate more action potentials when light is directed onto the receptive field. Respond to intensity of light – Off-center neurons: more action potentials when light is off or when light does not hit center of field. Respond to contrasts in light Interneurons present in inner layers and modify signal before signal leaves retina. Enhance borders and contours, increasing intensity at borders 15-44  Neuronal Pathways Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Left visual field 1 Each visual field is divided into a temporal and a nasal half. Temporal Nasal Nasal parts of part of part of visual fields 2 After passing through the lens, light from left visual left visual Temporal each half of a visual field projects to the field field Temporal 1 part of right opposite side of the retina. part of left visual field visual field 3 An optic nerve consists of axons extending from the retina to the optic Lens Optic chiasm. nerves Left eye 4 In the optic chiasm, axons from the nasal Nasal retina Temporal part of the retina cross and project to the retina (lateral (medial part) opposite side of the brain. Axons from the 3 part) 2 4 Optic chiasm Optic temporal part of the retina do not cross. Optic nerve Optic Optic chiasm tracts tracts Superior 5 Optic 5 An optic tract consists of axons that have Superior radiations colliculi passed through the optic chiasm (with or colliculi 6 Lateral geniculate without crossing) to the thalamus. Lateral nuclei of thalamus geniculate 6 The axons synapse in the lateral nuclei of geniculate nuclei of the thalamus. thalamus 7 Visual Collateral branches of the axons in the Optic cortex 8 optic tracts synapse in the superior radiations colliculi. Visual (b) Occipital lobe cortex 7 An optic radiation consists of axons from thalamic neurons that project to the (a) visual cortex. 8 The right part of each visual field (dark green and light blue) projects to the left side of the brain, and the left part of each visual field (light green and dark blue) projects to the right side of the brain. 15-45  Visual Fields Binocular vision: visual fields partially overlap yielding depth perception Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Left monocular Binocular Right monocular (c) 15-46  Eye Disorders Myopia: Nearsightedness Retinal detachment – Focal point too near lens, – Can result in complete image focused in front of blindness retina Glaucoma Hyperopia: Farsightedness – Increased intraocular – Image focused behind pressure by aqueous retina humor buildup Presbyopia Cataract – Degeneration of – Clouding of lens accommodation, Macular degeneration corrected by reading glasses – Common in older Astigmatism: Cornea or people, loss in acute vision lens not uniformly curved Diabetes Strabismus: Lack of – Dysfunction of parallelism of light paths peripheral circulation through eyes 15-47  15.4 Hearing and Balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. External ear Middle ear Inner ear Auricle Temporal Tympanic bone membrane External auditory Chorda Semicircular canal tympani canals Oval Vestibulocochlear window nerve Cochlear nerve Vestibule Cochlea Round window Auditory tube Malleus Incus Stapes Auditory ossicles in the middle ear Frontal section External ear: hearing. Terminates at eardrum (tympanic membrane). Includes auricle and external auditory canal Middle ear: hearing. Air-filled space containing auditory ossicles Inner ear: hearing and balance. Interconnecting fluid-filled tunnels and chambers within the temporal bone 15-48  External and Middle Ear External ear Middle ear – Separated from the inner air by – Auricle or pinna: elastic the oval and round windows cartilage covered with skin – Two passages for air – External auditory canal: Auditory or eustachian lined with hairs and tube: opens into pharynx, equalizes pressure ceruminous glands. Passage to mastoid air Produce cerumen cells in mastoid process – Tympanic membrane – Ossicles: malleus, incus, Thin membrane of two stapes: transmit vibrations from eardrum to oval window layers of epithelium with – Oval window: connection connective tissue between middle and inner ear. between Foot of the stapes rests here Sound waves cause it to and is held in place by annular ligament vibrate Border between external and middle ear 15-49  Middle Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anterior Superior ligament of malleus Incus Head of malleus Posterior ligament Anterior ligament of incus of malleus Chorda tympani Tensor tympani nerve muscle Stapedius muscle Auditory tube Tympanic membrane Posterior Handle of malleus Stapes Medial view 15-50 15-51  Inner Ear Labyrinths – Bony: chambers in the temporal bone Cochlea: hearing Vestibule: balance Semicircular canals: balance – Membranous: tunnels and chambers in the bony labyrinth Lymphs – Endolymph: in membranous labyrinth – Perilymph: space between membranous labyrinth and periosteum of bony labyrinth 15-52  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Inner Ear Bony labyrinth Membranous labyrinth (b) Bone Semicircular Bony labyrinth Membranous labyrinth canals Endosteum (boundary of Endolymph bony labyrinth) Fibrous bands from perilymphatic cells (c) Perilymph Bone Bony labyrinth Endosteum (boundary of Bony labyrinth) Perilymph Membranous labyrinth Endolymph Spiral ligament (d) Perilymph Oval Spiral window lamina Round (a) window Basilar membrane Vestibule Cochlea  Inner Ear Oval window communicates with vestibule which communicates with the scala vestibuli of the cochlea Scala vestibuli extends from oval window to helicotrema at cochlear apex Second cochlea chamber (scala tympani) from helicotrema to round window Scala vestibuli and tympani filled with perilymph 15-54  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endosteum of Inner Ear bone (boundary of bony labyrinth) Scala vestibuli (filled with Membranous Semicircular canals Cochlear perilymph) labyrinth nerve Vestibular membrane Tectorial membrane Vestibule Cochlear duct (filled with endolymph) Oval window Spiral ligament Cochlea Basilar membrane Spiral lamina Round window Scala tympani (filled with (bone) Helicotrema perilymph) Cochlear ganglion Endosteum (a) (b) Perilymphatic cells Perilymph Cochlear duct Vestibular membrane Tectorial membrane Stereocilia Cochlear nerve Basilar membrane Spiral lamina Supporting (bone) cells Spiral Outer hair Spiral ligament Hair cell cells organ Inner hair (c) cell Nerve endings of cochlear nerve (d) 15-56  Inner Ear Wall of scala vestibuli is vestibular membrane Wall of scala tympani is basilar membrane Cochlear duct (scala media): space between vestibular and basilar membranes. Filled with endolymph Width of basilar membrane increases from 0.04 mm near oval window to 0.5 mm near helicotrema – Near oval window basilar membrane responds to high- frequency vibrations – Near helicotrema responds to low-frequency vibrations 15-57  Inner Ear Spiral organ (organ of Corti): cells in cochlear duct Contain hair cells (sensory cells) with hair-like projections at the apical ends. These are microvilli called stereocilia. Basilar region of hair cells covered by synaptic terminals of sensory neurons Cell bodies of afferent neurons grouped into cochlear (spiral) ganglion Afferent fibers form the cochlear nerve 15-58  Inner Ear Hair cells arranged in rows. Of Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. inner hair cells (responsible for hearing) and outer hair cells Tip link (regulate tension on basilar membrane) Hair bundle: stereocilia of one Stereocilia inner hair cell Tip link (gating spring) attaches tip of each stereocilium in a hair bundle to the side of the next longer stereocilium. As stereocilia bend, they open K+ gates (mechanically gated ion channel) (a) 15-59  Auditory Function Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Higher amplitude (higher volume) Amplitude (volume) One cycle of tuning fork Lower amplitude (lower volume) Tuning fork Less Compressed compressed Compressed (b) Time air air Amplitude (volume) air Amplitude (volume) Lower frequency Higher frequency (lower pitch) (higher pitch) Sound wave (a) Time (c) Time Vibrations produce sound waves – Volume or loudness: function of wave amplitude – Pitch: function of wave frequency – Timbre: resonance quality or overtones of sound 15-60  Effect of Sound Waves on Cochlear Structures Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Oval window Stapes Incus Cochlear nerve Space between Malleus Scala vestibuli bony labyrinth Tympanic Scala tympani and membranous membrane labyrinth (contains 3 Cochlear duct perilymph) 2 (contains endolymph) External 4 auditory canal 1 Vestibular 5 membrane Membranous Basilar labyrinth 7 membrane Round window 6 Tectorial membrane Auditory tube Spiral organ Sound waves strike the tympanic membrane Vibration of the endolymph causes displacement of the and cause it to vibrate. basilar membrane. Short waves (high pitch), cause displacement of the basilar membrane near the oval window, Vibration of the tympanic membrane causes the and longer waves (low pitch) cause displacement of the malleus, the incus, and the stapes to vibrate. basilar membrane some distance from the oval window. Movement of the basilar membrane is detected in the hair The foot plate of the stapes vibrates in the oval cells of the spiral organ, which are attached to the basilar window. membrane. Vibrations of the perilymph in the scala vestibuli Vibration of the foot plate causes the and of the basilar membrane are transferred to the perilymph in the scala vestibule to vibrate. perilymph of the scala tympani. Vibrations in the perilymph of the scala tympani are Vibration of the perilymph causes the transferred to the round window, where they are dampened. vestibular membrane to vibrate, which causes vibrations in the endolymph. 15-61  Muscles of the Middle Ear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Tensor tympani: inserts Anterior Superior ligament on malleus; innervated Incus of malleus Head of malleus by cranial nerve V Posterior ligament of incus Anterior ligament of malleus Tensor tympani Stapedius: inserts on Chorda tympani stapes and innervated by muscle nerve Auditory tube Stapedius muscle Tympanic membrane Posterior Handle of malleus cranial nerve VII Stapes Attenuation reflex: muscles contract during Medial view loud noises and prevent damaging vibrations 15-62 Effect of Sound Waves on Points Along the Basilar Membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Base (near oval window) Apex (near helicotrema) (highest-pitched (lowest-pitched sounds) sounds) 1500 3000 Hz Hz 600 Hz 200 20,000 Hz Hz 800 Hz 1000 4000 Hz Hz 7000 Hz 5000 Hz Base Apex 0.04 mm Relative 0.5 mmwidth of basilar membrane 7000 200 Hz Hz (high- (low- 1000 frequency frequency Hz sounds) sounds) Basilar membrane 15-63  Sensitivity of Hearing Fine-tuning tension on basilar membrane – More than 90% of afferent axons of the cochlear ganglion synapse with inner hair cells, 10-30/hair cells. – A few small-diameter afferent axons synapse with rows of outer hair cells. – Outer hair cells receive efferent input causing them to shorten. Tuning hair cells to specific frequencies – Actin filaments in hair cells attach to K+ gated channels and can move them along the cell membrane and tighten or loosen the spring. Hair cells tuned to very specific frequencies. Localization of pitch along the cochlea – Afferent cochlear nerve fibers send action potentials to superior olivary nucleus in medulla oblongata. These are compared to one another and strongest is taken as standard. – Efferent action potentials inhibit other action potentials. Action potentials from maximum vibration go to cortex and are perceived 15-64  Neuronal Pathways for Hearing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Sensory axons from the cochlear ganglion terminate in the cochlear nucleus in the brainstem. 2 Axons from the neurons in the cochlear nucleus project to the superior olivary nucleus or to the inferior colliculus. Auditory Thalamus 4 Auditory cortex 3 Axons from the inferior 3 cortex colliculus project to the medial geniculate nucleus of the thalamus. Medial 2 geniculate nucleus 4 Thalamic neurons project to the Cochlear auditory cortex. ganglionNerve to 5 2 tensor Inferior colliculus tympani 5 Neurons in the superior olivary nucleus send axons to Vestibulocochlear 1 Superior olivary the inferior colliculus, back nerve nucleus to the inner ear, or to motor Cochlear 5 nuclei in the brainstem that nucleus send efferent fibers to the Nerve to middle ear muscles. stapedius 15- Frontal section 65  Balance Static labyrinth: utricle and saccule of the vestibule – Evaluates position of head relative to gravity – Detects linear acceleration and deceleration (as in a car) Kinetic labyrinth: semicircular canals – Evaluates movement of the head in three dimensional space 15-66  Static Labyrinth Utricle has macula oriented parallel to base of skull Saccula has macula oriented perpendicular to base of skull Macula: specialized epithelium of supporting columnar cells and hair cells with numerous stereocilia (microvilli) and one cilium (kinocilium) embedded in gelatinous mass weighted by otoliths – Gelatinous mass moves in response to gravity bending hair cells and initiating action potentials – Otoliths stimulate hair cells with varying frequencies – Patterns of stimulation translated by brain into specific information about head position or acceleration 15-67  Static Labyrinth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Otoliths Kinocilium (d) Otolithic membrane Stereocilia (microvilli) Utricular macula Saccular macula Nerve fibers of vestibular nerve (c) Utricle Part of Hair cell Vestibule Supporting cells Saccule macula (a) (b) d: © Susumu Nishinag/Photo Researchers, Inc. Function of Vestibule in Maintaining Balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Endolymph in Force of gravity utricle Otolithic membrane Hair cell Macula Supporting cell Vestibular nerve fibers (a) (b) a-b: © Trent Stephens 15-69  Kinetic Labyrinth Three semicircular canals filled with Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or endolymph: transverse plane, display. coronal plane, sagittal plane Base of each expanded into Semicircular canals ampulla with sensory epithelium Ampullae (crista ampullaris) Vestibular Cupula suspended over crista hair nerve cells. Acts as a float displaced by Cupula fluid movements within semicircular (a) canals Displacement of the cupula is most intense when the rate of head movement changes, thus this Cupula Stereocilia system detects changes in the rate of movement rather than movement Crista Hair cell alone. ampullaris (b) Nerve fibers to vestibular(c) nerve 15-70  Neuronal Pathways for Balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1 Sensory axons from the vestibular ganglion pass through the vestibular nerve to the vestibular nucleus, which also receives input from several other sources, such as Vestibular proprioception from the legs. area 2 Vestibular neurons send axons to Posterior the cerebellum, which influences ventral 5 postural muscles. nucleus Thalamus 4 3 Vestibular neurons also send axons to motor nuclei (oculomotor, trochlear, and abducens), which control extrinsic Cerebellum 3 eye muscles. 3 Oculomotor Vestibular nucleus 4 Vestibular neurons also send axons nerve to the posterior ventral nucleus of 3