Module 8C. Special Senses PDF

17/10/2024 OLFACTION...

17/10/2024 OLFACTION sense of smell occurs in response to odorants – 1000 different odorant receptors Olfactory epithelium in superior portion of the nasal cavity senses of smell (olfaction), taste, vision, Olfactory Epithelium and Olfactory Bulb. hearing, and balance a. A sagittal section through the lateral wall of the nasal cavity shows the olfactory nerves, olfactory bulb, and olfactory tract. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 2 10 million olfactory neurons Action of Odorant Binding to Membrane Receptor of Olfactory Hair. - bipolar 1.Each odorant receptor molecule is Dendrites of olfactory neurons associated with a G protein. have enlarged ends called olfactory vesicles 2.Binding of an odorant to the receptor molecule activates the G Olfactory hairs are cilia of protein. olfactory neuron embedded in mucus 3.The G protein activates adenylate Odorants dissolve in mucus. cyclase. Odorants attach to receptors, 4.Adenylate cyclase is an enzyme cilia depolarize and initiate that catalyzes the formation of action potentials in olfactory cyclic AMP (cAMP) from ATP. neurons Olfactory Epithelium and 5.cAMP in these cells causes Na+ Olfactory Bulb. One receptor may respond to and Ca++ channels to open. The more than one type of odor influx of ions into the olfactory b. The olfactory neurons lie within hairs results in depolarization and the olfactory epithelium. The axons Olfactory epithelium is replaced as it wears down. Olfactory the production of action potentials of olfactory neurons pass through in the olfactory neurons. the cribriform plate to the olfactory neurons are replaced by basal bulb. cells every two months. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 3 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 4 Primary Classes of Smells/Odors: Olfactory Processing: Camphoraceous (ex., mothballs) Majority of neurons in the olfactory tracts project to the Musky central olfactory cortex areas in the temporal and frontal Floral lobes where they are processed to allow us to perceive odors. Includes the piriform cortex, amygdala, and orbitofrontal Pepperminty cortex Ethereal (fresh pears) Secondary olfactory areas involved with emotional and Pungent autonomic responses to smell. Putrid Includes the hypothalamus, hippocampus, and limbic system.  May be as many as 50 primary odors exist Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 5 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 6 1  17/10/2024 Olfaction Process: 1. Nasal cavity contains a thin film of mucous where odors become dissolved. 2. Olfactory neurons are located in the mucous. Dendrites of olfactory neurons are enlarged and contain cilia. 3. Dendrites pick up odor, depolarize, and carry odor to axons in olfactory bulb (cranial Olfactory Cortex and Neuronal Pathways. nerve I). Olfactory Epithelium and Olfactory Bulb The olfactory neurons lie within the 4. Frontal and temporal lobes olfactory epithelium. The axons of olfactory process odor. neurons pass through the cribriform plate to the olfactory bulb. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 7 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 8 TASTE Taste buds: sensory structures that detect taste Types of papillae: located on papillae on tongue, hard Filiform. Filament-shaped. Most numerous. No taste buds. palate, throat Vallate. Largest, least numerous. 8 to 12 in V along border inside each taste bud are 40 taste between anterior and posterior parts of the tongue. Have cells; taste cells have microvilli taste buds. (gustatory hairs) extending into Foliate. Leaf-shaped. In folds on the sides of the tongue. taste pores Contain most sensitive taste buds. Decrease in number each taste cell has taste hairs that with age. extend into taste pores Tongue. Fungiform. Mushroom-shaped. Scattered irregularly over (a) Dorsal surface of the tongue. the superior surface of tongue. Look like small red dots (b) Section through a papilla showing the location interspersed among the filiform. Have taste buds. of taste buds. (c) Enlarged view of a section through a taste bud. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 9 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 10 Papillae (a) Dorsal surface of Histology of Taste Buds: the tongue. (b) Filiform papilla Consist of three major cells types: (c) Vallate papilla Taste cells (d) Foliate papilla Basal cells Supporting cells  A taste bud has about 50 taste cells, each having several microvilli called taste hairs.  Taste hairs extend from apex of the taste cell through a taste pore. Taste cells are replaced every 10 days. (e) Fungiform papilla; (f) taste bud; (g) a taste cell. Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 11 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 12 2  17/10/2024 Taste Types: Taste Sour. Most sensitive receptors on lateral aspects of the tongue. Substances called testants, dissolve in saliva, enter the taste pores, then stimulate the taste cells. Salty. Most sensitive receptors on tip of tongue. Shares lowest sensitivity with sweet. Anything with Na+ causes depolarization Texture and temperature affect the perception of taste. plus other metal ions. Craved by humans. Very rapid adaptation, both at level of taste bud and within Bitter. Most sensitive receptors on posterior aspect. Highest the CNS. sensitivity. Sensation produced by alkaloids, which are toxic. Taste influenced by olfaction. Sweet. Most sensitive receptors on tip of tongue. Shares lowest sensitivity with salty. Sugars, some carbohydrates, and some Different tastes have different thresholds with bitter being proteins (NutraSweet: aspartame). Craved by humans. the taste to which we are most sensitive. Many alkaloids (bitter) are poisonous. Umami (Glutamate). Scattered sensitivity. Caused by amino acids. Craved by humans. All taste buds can detect all five tastes but are usually more sensitive to one. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 13 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 14 Stimulation of Taste Receptors: Pathways for the Sense of Taste: Pathways for the Sense of Sour: Hydrogen ions of acids cause depolarization of taste Taste. cells by one of three mechanisms: The facial nerve (anterior two-thirds of the tongue), Enter the cells directly through H+ channels glossopharyngeal nerve (posterior one-third of the Bind to ligand-gated K+ channels and block exit of K+ from tongue), and vagus nerve cell (root of the tongue) all carry taste sensations. The Open ligand-gated channels for other positive ions and trigeminal nerve carries allow then to diffuse into the cell. tactile sensations from the anterior two-thirds of the Bitter: stimulate through G protein mechanism tongue. The chorda tympani from the facial Umami: amino acids like glutamate bind to receptors and nerve (carrying taste input) depolarize through a G protein mechanism. joins the trigeminal nerve. Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 15 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 16 VISUAL SYSTEM Neuronal Pathways for Taste: eyes, accessory structures, and sensory neurons eyes are housed within bony cavities called orbits Carried by three cranial nerves: visual input includes information about light and dark, movement Chorda tympani (part of Facial nerve, VII): carry and color; begins as action potentials originating in the eyes sensations from anterior two-third of tongue (except from action potentials move along the visual pathways and convey visual circumvallate papillae. information to the brain Glossopharyngeal nerve (IX): carries taste sensations from posterior one-third tongue, the vallate papillae,and superior pharynx. Vagus nerve (X): carries a few fibers for taste sensation from the tongue root and epiglottis. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 17 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 18 3  17/10/2024 Accessory Structures: Accessory Structures: protect, lubricate, and move the eye Conjunctiva: thin mucous membrane that covers inner surface of eyelid and anterior surface of eye Eyelid/Eyelashes: help lubricate Eyebrow the surface of 5 tissue layers the eye protects from sweat protects from foreign The Eye and Its Accessory Structures. objects shade from sun lubricates by blinking Sagittal section through the eye. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 19 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 20 Accessory Structures: Accessory Structures: Lacrimal apparatus Extrinsic Eye Muscles consists of a lacrimal gland situated in the superior lateral corner of the each eyeball has six extrinsic eye orbit and a nasolacrimal duct and muscles attached to its surface associated structures in the inferior medial corner of the orbit for movement of each eyeball superior, inferior, medial, and produce tears to lubricate and lateral rectus muscles - run more cleanse the eye; contain an enzyme or less straight from their origins in that helps combat eye infections the posterior portion of the orbit to fluid produced by the lacrimal glands their insertion sites on the eye, to evaporates from the surface of the attach to the four quadrants of the eye, but excess tears are collected in eyeball Extrinsic Eye Muscles. the medial angle of the eyes by small ducts called lacrimal canaliculi The Eye and Its Accessory Structures. superior and inferior oblique Extrinsic muscles of the right eye as muscles are located at an angle to seen from a lateral view with the Lacrimal apparatus. lateral wall of the orbit removed. The canaliculi open into a lacrimal sac, the long axis of the eyeball an enlargement of the nasolacrimal medial rectus muscle cannot be seen duct from this view. Access the text alternative for slide images. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 21 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 22 Anatomy of Eye Fibrous Tunic of Eyeball outermost tunic eyeball is hollow, fluid- filled sphere Sclera: posterior 4/5th of the eye; eyeball wall composed firm, white outer of 3 layers or tunics connective tissue helps maintain eye shape, outer, fibrous tunic provides attachment sites consists of the sclera for muscles, protects and cornea. internal structures Sagittal Section of the Eye, Demonstrating Its Tunics. Sagittal Section of the Eye, Demonstrating Its seen as “white of the eye” middle, vascular tunic Tunics. The wall of the eyeball consists of consists of the choroid, The wall of the eyeball consists of three tunics, each Cornea: three tunics, each of which is composed of specific components. ciliary body, and iris of which is composed of specific components. The anterior 1/5th of the eye; The fibrous tunic includes the sclera fibrous tunic includes the sclera and cornea. The vascular tunic includes the choroid, ciliary body, and transparent structure that and cornea. The vascular tunic inner nervous tunic iris. The nervous tunic consists of the retina. covers iris and pupil includes the choroid, ciliary body, consists of the retina allows light to enter and and iris. The nervous tunic consists of the retina. focuses light Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 23 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 24 4  17/10/2024 Vascular Tunic of the Eyeball Vascular Tunic of the Eyeball middle tunic Iris: contains blood supply Choroid: colored part of eye black part (melanin) attached to anterior margin of ciliary body, anterior to the lens delivers O2 and nutrients to retina contractile stricture made up of Ciliary body: smooth muscle helps hold lens in place surrounds and regulates pupil Ciliary muscle: Pupil: controls shape of lens via regulates amount of light entering suspensory ligaments Lens and Ciliary Body. Iris. Lens: Contraction and relaxation of the ciliary muscles adjust lots of light = constricted (a) Circular smooth muscles of the iris the tension in the suspensory ligaments, which are constrict the pupil. flexible, biconvex, transparent attached to the lens. Alterations in the tension in the little light = dilated (b) Radial smooth muscles of the iris dilate suspensory ligaments changes the shape of the lens. disc the pupil. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 25 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 26 innermost tunic; with neurons Nervous Tunic of the Eyeball Nervous Tunic of the Eyeball sensitive to light Rods: Retina: photoreceptor sensitive to light covers posterior 5/6 of eye 20 times more rods than cones contains 2 layers – outer pigmented retina and inner can function in dim light sensory retina do not provide color vision Pigmented retina: outer layer Cones: keeps light from reflecting back require more light in eye Retina. provides color vision Sensory retina: Retina. (b) Colorized electron micrograph of rods and cones. (c) Rod cell. (d) Cone cell. (a) Enlarged section through the three types of cones, each contains photoreceptors (rods and (e) Enlargement of the discs in the outer retina, with its major layers labeled sensitive to a different color: segment. (f) Enlargement of one of the discs, cones) and interneurons blue, green, or red showing the relationship of rhodopsin to the responds to light membrane. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 27 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 28 Nervous Tunic of the Eyeball Effect of Light on Rhodopsin 1. Rhodopsin is composed of opsin and retinal. outer segments of rod and 2. Light causes retinal to change shape, which cone cells are modified by activates rhodopsin. numerous foldings of the 3. Activated rhodopsin stimulates cell changes cell membrane to form that result in vision. discs 4. Following rhodopsin activation, retinal detaches from opsin. Rod photoreceptors 5. Energy from ATP is required to bring retinal contain a photosensitive back to its original form. pigment called rhodopsin Retina. 6. Retinal recombines with opsin to form with a protein opsin (b) Colorized electron micrograph of rods and rhodopsin (return to step 1). loosely bound to a yellow cones. (c) Rod cell. (d) Cone cell. (e) Enlargement of the discs in the outer pigment called retinal segment. (f) Enlargement of one of the discs, Effect of Light on Rhodopsin. showing the relationship of rhodopsin to the When exposed to light, rhodopsin is activated as retinal changes membrane. shape and detaches from opsin. ATP is needed to recombine the opsin and retinal. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 29 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 30 5  17/10/2024 The Retina Macula: The Retina small spot near center of retina Optic disc: Fovea centralis: white spot medial to macula blood vessels enter eye and center of macula spread over retina where light is focused when axons exit as optic nerve Ophthalmoscopic View of the Retina. looking directly at an object no photoreceptors Ophthalmoscopic View of the Retina. (a) This view shows the posterior wall of only cones the left eye as seen through the pupil. called blind spot This view shows the posterior wall of the left eye Notice the vessels entering the eye as seen through the pupil. Notice the vessels through the optic disc. The macula, with entering the eye through the optic disc. The ability to discriminate fine the fovea centralis in the center, is macula, with the fovea centralis in the center, images located lateral to the optic disc. is located lateral to the optic disc. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 31 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 32 Chambers of the Eye Chambers of the Eye Anterior chamber: Vitreous chamber: located between cornea and lens located in retina region filled with aqueous humor (watery) filled with vitreous humor: jelly-like aqueous humor helps maintain pressure, refracts substance light, and provide nutrients to Sagittal Section of the Eye, Demonstrating Its inner surface of eye Sagittal Section of the Eye, Demonstrating vitreous humor helps Tunics. Its Tunics. maintain pressure, The wall of the eyeball consists of three tunics, The wall of the eyeball consists of three tunics, Posterior chamber: each of which is composed of specific holds lens and retina in each of which is composed of specific components. The fibrous tunic includes the sclera and cornea. located behind anterior components. The fibrous tunic includes the sclera and cornea. The vascular tunic includes place, refracts light The vascular tunic includes the choroid, ciliary body, and iris. The nervous tunic consists of the chamber the choroid, ciliary body, and iris. The nervous retina. tunic consists of the retina. contains aqueous humor Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 33 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 34 Functions of the Eye: Visual Pathway Light Refraction Focusing Images on Retina 1. Each visual field is divided into temporal and Accommodation: nasal halves. bending of light 2. After passing through the lens, light from each focal point (FP) where light rays changes in shape of the lens so half of a visual field projects to the opposite converge image can be focused on retina side of the retina stimulating receptors. enables eye to focus on images 3. Axons from the retina pass through the optic occurs anterior to retina nerve to the optic chiasma, where some closer than 20 feet cross. Axons from the nasal retina cross, object is inverted and those from the temporal retina do not. 4. Optic tracts extend from the optic chiasm (with or without crossing) to the thalamus. Collateral branches of the axons in the optic tract synapse in the superior colliculi of the midbrain. 5. Optic radiations extend from the thalamus to the visual cortex of the occipital lobe. 6. 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 Visual Pathway. Focus by the Eye. The focal point (FP) is where light rays cross. (a) When viewing a distant (light green and dark blue) projects to the image, the lens is flattened, and the image is focused on the retina. (b) In accommodation for right side of the brain. (a) Pathways for both eyes near vision, the lens becomes more rounded, allowing the image to be focused on the retina (superior view). Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 35 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 36 6  17/10/2024 Color Blindness Eye Disorders: Astigmatism. Retinal detachment. absence of Cornea or lens not uniformly Can result in complete perception of one or curved. blindness. more colors Diplopia. Glaucoma. loss may involve Double vision Increased intraocular pressure perception of all by aqueous humor buildup. three colors or of one Colorblindness. These color blindness charts demonstrate the Complete or partial absence of Cataract. or two colors differences in color perception associated with color perception. Clouding of lens. most forms of color some forms of color blindness. Conjunctivitis. Macular degeneration. blindness occur more (a) A person with normal vision can see the Inflammation of the conjunctiva. Common in older people, loss of frequently in males number 74, whereas a person with red- sharp central vision. and are X-linked green color blindness sees the number 21. Stye. genetic traits Infection of eyelash hair follicle. Diabetic retinopathy. (b) A person with normal vision can see the Optic nerve degeneration, number 5. A person with red-green color cataracts, retinal detachment. blindness sees the number 2. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 37 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 38 Anatomy and Function of the Ear HEARING AND BALANCE External ear consists of the tympanic membrane (eardrum) auricle and the external auditory is stretched across the external canal auditory canal The Ear Middle ear contains the three malleus, incus, and stapes auditory ossicles connect the tympanic membrane organs of hearing and balance to the oval window of the inner are located in the ears. ear each ear is divided into three auditory or eustachian tube areas: connects the middle ear to the pharynx and equalizes pressure 1. external ear – for hearing middle ear is also connected 2. middle ear – for hearing to the mastoid air cells Structure of the Ear. 3. inner ear – for hearing and A medial view of the three regions of the ear: Structure of the Ear. balance the external ear, the middle ear, and the inner A medial view of the three regions of ear. the ear: the external ear, the middle ear, and the inner ear. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 39 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 40 inner ear has three parts: the semicircular canals, the vestibule, and the cochlea. cochlea is a canal shaped like a snail’s shell cochlea is divided into three compartments by the vestibular and basilar membranes spiral organ consists of hair cells that attach to the basilar and tectorial membranes Structure of the Inner Ear. Structure of the Inner Ear. (a) Bony labyrinth. The outer surface (gray) is the periosteum lining (a) Bony labyrinth. The outer surface (gray) is the periosteum lining the inner surface of the bony the inner surface of the bony labyrinth. labyrinth. (b) In this cross section of the cochlea, the outer layer (b) In this cross section of the cochlea, the outer layer is the periosteum is the periosteum lining the inner surface of the (c) An enlarged section of the cochlear duct lining the inner surface of the bony labyrinth. The membranous bony labyrinth. The membranous labyrinth is (membranous labyrinth). very small in the cochlea and consists of the labyrinth is very small in the cochlea and consists of the (d) A greatly enlarged individual sensory hair vestibular and basilar membranes. The space cell. vestibular and basilar membranes. The space between the between the membranous and bony labyrinths consists of two parallel tunnels: the scala vestibuli (e) Scanning electron micrograph of the membranous and bony labyrinths consists of two parallel and the scala tympani. microvilli of a hair cell. tunnels: the scala vestibuli and the scala tympani. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 41 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 42 7  17/10/2024 Effect of Sound Waves on Middle and Inner Ear Structures Effect of Sound Waves on Middle and Inner Ear Structures. Sound waves in the air are conducted through the ear until they stimulate hair cells in the spiral organ. Structure of the Inner Ear. (c) An enlarged section of the cochlear duct (membranous labyrinth). (d) A greatly enlarged individual sensory hair cell. (e) Scanning electron micrograph of the microvilli of a hair cell. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 43 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 44 Hearing Process Balance (Equilibrium) Static equilibrium: associated with vestibule evaluates position of head relative to gravity Dynamic equilibrium: associated with semicircular canals evaluates changes in direction and rate of Neuronal Pathways for Hearing. head movement Action potentials generated at the spiral organ are conducted to the temporal lobes of the cerebrum Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 45 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 46 Vestibule: Function of the Vestibule in Maintaining Balance inner ear contains utricle and saccule Maculae: specialized patches of epithelium in utricle and saccule surrounded by endolymph contain hair cells Location and Structure of the Macula. (a) Location of the utricular and Otoliths: saccular maculae within the particles of protein and calcium vestibule. carbonate embedded in a gelatinous (b) Enlargement of the utricular substance that moves in response to macula, showing hair cells and Function of the Vestibule in Maintaining Balance. gravity otoliths. (c) Enlarged hair cell, showing the (a) In an upright position, the maculae don’t move. microvilli of hair cells are embedded in microvilli. the gelatinous substance and initiate (b) When the position of the head changes, as when a person bends over, (d) Colorized scanning electron the maculae respond by moving in the direction of gravity. action potentials when bent micrograph of otoliths. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 47 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 48 8  17/10/2024 Dynamic equilibrium evaluates Function of the Crista Ampullaris movements of the head. The inner ear contains three semicircular canals, arranged perpendicular to each other. The ampulla of each semicircular canal contains a crista ampullaris, which has hair cells with microvilli embedded in a gelatinous mass, the cupula. Function of the Crista Ampullaris. (a) As a person begins to tumble, the semicircular canals (b) move in the Semicircular Canals. same direction as the body (blue arrow). The endolymph in the semicircular (a) Location of the ampullae of the semicircular canals tends to stay in place as the body and the crista ampullaris begin to canals. move. As a result, the cupula is displaced by the moving endolymph (red (b) Enlargement of the crista ampullaris, arrow) in a direction opposite the direction of movement. showing the cupula and hair cells. (c) Enlargement of a hair cell. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 49 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 50 EFFECTS OF AGING ON THE SPECIAL SENSES: Neuronal Pathways for Balance Slight loss in ability to detect odors. axons from the maculae and the cristae ampullares extend to the vestibular nucleus of the medulla Decreased sense of taste. oblongata Lenses of eyes lose flexibility - presbyopia fibers from the medulla run to the spinal cord, Development of cataracts, macular degeneration, cerebellum, cortex, and nuclei that control the extrinsic glaucoma, diabetic retinopathy. eye muscles Decline in visual acuity and color perception. balance also depends on proprioception and visual input Presbyacusis – age-related hearing loss Hair cells in the cochlea, utricle, saccule, and ampulla decrease. More falls due to instability and vertigo. Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 51 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 52 Copyright 2022 © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 53 9