Special senses

Special senses - Special Senses Special Chemical Senses...

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Unformatted text preview: Special Senses Special Chemical Senses Chemical Chemical senses – gustation (taste) and olfaction (smell) Their chemoreceptors respond to chemicals in aqueous solution Taste – to substances dissolved in saliva Smell – to substances dissolved in fluids of the nasal membranes Taste Buds Taste Most of the 10,000 or so taste buds are found on the tongue Taste buds are found in papillae of the tongue mucosa Papillae come in three types: filiform, fungiform, and circumvallate Fungiform and circumvallate papillae contain taste buds Taste Buds Taste Anatomy of a Taste Bud Anatomy Each gourd­shaped taste bud consists of three major cell types Supporting cells – insulate the receptor Basal cells – dynamic stem cells Gustatory cells – taste cells Taste Sensations Taste There are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some amino acids Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamate Physiology of Taste Physiology In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical: Depolarizes the taste cell membrane, releasing neurotransmitter Initiates a generator potential that elicits an action potential Taste Transduction Taste The stimulus energy of taste is converted into a nerve impulse by: Na+ influx in salty tastes H+ in sour tastes (by directly entering the cell, by opening cation channels, or by blockade of K+ channels) Gustducin in sweet and bitter tastes Gustatory Pathway Gustatory Cranial Nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medulla These impulses then travel to the thalamus, and from there fibers branch to the: Gustatory cortex (taste) Hypothalamus and limbic system (appreciation of taste) Gustatory Pathway Gustatory Influence of Other Sensations on Taste on Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors also influence tastes Temperature and texture enhance or detract from taste Sense of Smell Sense The organ of smell is the olfactory epithelium, which covers the superior nasal concha Olfactory receptor cells are bipolar neurons with radiating olfactory cilia Olfactory receptors are surrounded and cushioned by supporting cells Basal cells lie at the base of the epithelium Sense of Smell Sense Physiology of Smell Physiology Olfactory receptors respond to several different odor­causing chemicals When bound to ligand these proteins initiate a G protein mechanism, which uses cAMP as a second messenger cAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potential Olfactory Pathway Olfactory Olfactory receptor cells synapse with mitral cells Glomerular mitral cells process odor signals Mitral cells send impulses to: The olfactory cortex The hypothalamus, amygdala, and limbic system Olfactory Transduction Process Olfactory Odorant binding protein Inactive Adenylate cyclase Odorant chemical Na+ Active Na+ influx causes depolarization ATP cAMP Cytoplasm Depolarization of olfactory receptor cell membrane triggers action potentials in axon of receptor Eye and Associated Structures Eye 70% of all sensory receptors are in the eye Eye and Associated Structures Eye Eye and Associated Structures Eye Most of the eye is protected by a cushion of fatand the bony orbit The orbit from above 1. dura mater lining the floor of ant. cranial fossa 2. roof of orbit 3. Periorbital fat Eye and Associated Structures Structures Most of the eye is protected by a cushion of fat and the bony orbit Eye and Associated Structures Eye Accessory structures include eyebrows, Eye and Associated Structures Structures Accessory structures include eyebrows, Eye and Associated Structures Eye Accessory structures include eyelids Eye and Associated Structures Structures Accessory structures include conjunctiva Eye and Associated Structures Structures Accessory structures include conjunctiva Eye and Associated Structures Structures Accessory structures include conjunctiva Eye and Associated Structures Structures Accessory structures include lacrimal apparatus Eye and Associated Structures Structures Accessory structures include extrinsic eye muscles Eyebrows Eyebrows Coarse hairs that overlie the supraorbital margins Functions include: Shading the eye Preventing perspiration from reaching the eye Eyebrows Eyebrows Orbicularis muscle – depresses the eyebrows Corrugator muscles – move the eyebrows medially and Palpebrae (Eyelids) (Eyelids) Protect the eye anteriorly Palpebral fissure – separates eyelids Canthi – medial and lateral angles (commissures) Palpebrae (Eyelids) Palpebrae Palpebral fissure – separates eyelids Palpebrae (Eyelids) Palpebrae Palpebral fissure – separates eyelids Caucasoid Mongoloid epicanthic fold Negroid Palpebrae (Eyelids) Palpebrae Canthi – medial and lateral angles (commissures) Palpebrae (Eyelids) Palpebrae Lacrimal caruncle – contains glands that secrete a whitish, oily secretion (Sandman’s eye sand) Palpebrae (Eyelids) Palpebrae Tarsal plates of connective tissue support the eyelids internally 1 Palpebrae (Eyelids) Palpebrae Levator palpebrae superioris – gives the upper eyelid mobility Palpebrae (Eyelids) (Eyelids) Levator palpebrae superioris – gives the upper eyelid mobility Palpebrae (Eyelids) (Eyelids) Eyelashes Project from the free margin of each eyelid Initiate reflex blinking Palpebrae (Eyelids) Palpebrae Conjunctiva Conjunctiva Transparent membrane that: Lines the eyelids as the palpebral conjunctiva Covers the whites of the eyes as the ocular conjunctiva Lubricates and protects the eye Lacrimal Apparatus Apparatus Consists of the lacrimal gland and associated ducts Lacrimal glands secrete tears Lacrimal Apparatus Lacrimal Tears Contain mucus, antibodies, and lysozyme Lacrimal Apparatus Lacrimal Tears Enter the eye via superolateral excretory ducts Lacrimal Apparatus Lacrimal Tears Exit the eye medially via the lacrimal punctum Lacrimal Apparatus Apparatus Tears Drain into the nasolacrimal duct Lacrimal Apparatus Lacrimal Extrinsic Eye Muscles Extrinsic Six straplike extrinsic eye muscles Enable the eye to follow moving objects Extrinsic Eye Muscles Extrinsic Six straplike extrinsic eye muscles Maintain the shape of the eyeball Extrinsic Eye Muscles Muscles Four rectus muscles originate from the annular ring Extrinsic Eye Muscles Extrinsic Four rectus muscles originate from the annular ring . Common tendinous ring Extrinsic Eye Muscles Extrinsic Two oblique muscles Extrinsic Eye Muscles Extrinsic Summary of Cranial Nerves and Muscle Actions Muscle Names, actions, and cranial nerve innervation of the extrinsic eye muscles Summary of Cranial Nerves and Muscle Actions Muscle Names, actions, and cranial nerve innervation of the extrinsic eye muscles Structure of the Eyeball Structure A slightly irregular hollow sphere with anterior and posterior poles Structure of the Eyeball Structure The wall is composed of three tunics – fibrous, vascular, and sensory Structure of the Eyeball Structure The internal cavity is filled with fluids called humors Structure of the Eyeball Structure The lens separates the internal cavity into anterior and posterior segments Structure of the Eyeball Structure Fibrous Tunic Fibrous Forms the outermost coat of the eye and is composed of: Opaque sclera (laterally & posteriorly) Clear cornea (anteriorly) Fibrous Tunic Fibrous The sclera protects the eye and anchors extrinsic muscles The cornea lets light enter the eye The Chamber of eye Chamber of eye 1. Anterior chamber 2. Posterior chamber Refracting media Refracting media 1. 2. 3. 4. Cornea Aqueous humor Lens Vitreous humor Vascular Tunic (Uvea): Choroid Region Region Has three regions: choroid Vascular Tunic (Uvea): Choroid Region Region Has three regions: ciliary body Vascular Tunic (Uvea): Choroid Region Region Has three regions: iris Vascular Tunic (Uvea): Choroid Region Region Has three regions: iris Vascular Tunic: Ciliary Body Vascular A thickened ring of tissue surrounding the lens Composed of smooth muscle bundles (ciliary muscles) Anchors the suspensory ligament that holds the lens in place Smooth muscle Smooth Smooth muscle Smooth Smooth muscle Smooth Vascular Tunic: Iris Vascular The colored part of the eye Vascular Tunic: Iris Vascular Pupil – central opening of the iris Regulates the amount of light entering the eye during: Close vision and bright light – pupils constrict Pupil – central opening of the iris Regulates the amount of light entering the eye Regulates Chamber of eye Chamber of eye 1. Anterior chamber 2. Posterior chamber Refracting media Refracting media 1. 2. 3. 4. Cornea Aqueous humor Lens Vitreous humor Vascular Tunic: Iris Vascular The colored part of the eye Pupil – central opening of the iris Regulates the amount of light entering the eye during: Distant vision and dim light – pupils dilate Vascular Tunic: Iris Iris The colored part of the eye Pupil – central opening of the iris Regulates the amount of light entering the eye during: Changes in emotional state – pupils dilate when the subject matter is appealing or requires problem­ solving skills Pupil Dilation and Constriction Pupil Sensory Tunic: Retina Sensory A delicate two­layered membrane Sensory Tunic: Retina Sensory Pigmented layer – the outer layer that absorbs light and prevents its scattering Sensory Tunic: Retina Retina Neural layer, which contains: Photoreceptors that transduce light energy Bipolar cells and ganglion cells Amacrine and horizontal cells Sensory Tunic: Retina Sensory The Retina: Ganglion Cells The Ganglion cell axons: Run along the inner surface of the retina Leave the eye as the optic nerve Bipolar cells Bipolar Photoreceptors Photoreceptors Pigment Layer Pigment The Retina: Ganglion Cells The Ganglion cell axons: Run along the inner surface of the retina Leave the eye as the optic nerve The Retina: Optic Disc The The optic disc: Is the site where the optic nerve leaves the eye Lacks photoreceptors (the blind spot) The Retina: Optic Disc The Most sensitive to changes in light Rods Rods The rods are not as adept in discerning colors See better in shades than in hues. Location is in peripheral part of the retina and used Most sensitive to changes in light Rods Rods The rods are not as adept in discerning colors See better in shades than in hues. Location is in peripheral part of the retina and used Rods Rods Most sensitive to changes in light The rods are not as adept in discerning colors See better in shades than in hues. Location is in peripheral part of the retina and are used in peripheral vision Respond in dim light The Retina: Photoreceptors Photoreceptors Cones: Respond to bright light Have high­acuity color vision Are found in the macula lutea Are concentrated in the fovea centralis Blood Supply to the Retina Blood The neural retina receives its blood supply from two sources The outer third receives its blood from the choroid The inner two­thirds is served by the central artery and vein Blood Supply to the Retina Blood Small vessels radiate out from the optic disc and can be seen with an ophthalmoscope Inner Chambers and Fluids Inner The lens separates the internal eye into anterior and posterior segments Inner Chambers and Fluids Inner The posterior segment is filled with a clear gel called vitreous humor that: Transmits light Supports the posterior surface of the lens Inner Chambers and Fluids Inner The posterior segment is filled with a clear gel called vitreous humor that: Holds the neural retina firmly against the pigmented layer Contributes to intraocular pressure Anterior Segment Anterior Composed of two chambers Anterior – between the cornea and the iris Anterior Segment Anterior Composed of two chambers Posterior – between the iris and the lens Anterior Segment Anterior Aqueous humor A plasmalike fluid that fills the anterior segment Drains via the canal of Schlemm Supports, nourishes, and removes wastes Anterior Segment Anterior Lens Lens A biconvex, transparent, flexible, avascular structure that: Allows precise focusing of light onto the retina Is composed of epithelium and lens fibers Lens Lens Lens epithelium – anterior cells that differentiate into lens fibers Lens Lens Lens fibers – cells filled with the transparent protein crystallin Lens Lens With age, the lens becomes more compact and dense and loses its elasticity Light Light Electromagnetic radiation – all energy waves from short gamma rays to long radio waves Our eyes respond to a small portion of this spectrum called the visible spectrum Light Light Electromagnetic radiation – all energy waves from short gamma rays to long radio waves Our eyes respond to a small portion of this spectrum called the visible spectrum Light Light Different cones in the retina respond to different wavelengths of the visible spectrum Refraction and Lenses Refraction When light passes from one transparent medium to another its speed changes and it refracts (bends) Refraction and Lenses Refraction Light passing through a convex lens (as in the eye) is bent so that the rays converge to a focal point Refraction and Lenses Refraction When a convex lens forms an image, the image is upside down and reversed right to left Refraction and Lenses Refraction Focusing Light on the Retina Chamber of eye Chamber of eye 1. Anterior chamber 2. Posterior chamber Refracting media Refracting media 1. 2. 3. 4. Cornea Aqueous humor Lens Vitreous humor Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, Pathway and the neural layer of the retina to the photoreceptors and Focusing Light on the Retina Focusing Light is refracted: At the cornea Entering the lens Leaving the lens The lens curvature and shape allow for fine focusing of an image Focusing for Distant Vision Focusing Light from a distance needs little adjustment for proper focusing Far point of vision – the distance beyond which the lens does not need to change shape to focus (20 ft.) Focusing for Close Vision Focusing Close vision requires: Accommodation – changing the lens shape by ciliary muscles to increase refractory power http://micro.magnet.fsu.edu/primer/java/humanvision/accommodation/ Focusing for Close Vision Focusing Close vision requires: Constriction – the pupillary reflex constricts the pupils to prevent divergent light rays from entering the eye Focusing for Close Vision Focusing Close vision requires: Convergence – medial rotation of the eyeballs toward the object being viewed Focusing for Close Vision Focusing Problems of Refraction Problems Emmetropic eye – normal eye with light focused properly Problems of Refraction Problems Myopic eye (nearsighted) – the focal point is in front of the retina Corrected with a concave lens Problems of Refraction Problems Hyperopic eye (farsighted) – the focal point is behind the retina Corrected with a convex lens Photoreception: Functional Anatomy of Photoreceptors of Photoreception – process by which the eye detects light energy Photoreception: Functional Anatomy of Photoreceptors Functional Rods and cones contain visual pigments (photopigments) Arranged in a stack of disklike infoldings of the plasma membrane that change shape as they absorb light Photoreception: Functional Anatomy of Photoreceptors Photoreceptors Rods and cones contain visual pigments (photopigments) Arranged in a stack of disklike infoldings of the plasma membrane that change shape as they absorb light Photoreception: Functional Anatomy of Photoreceptors Photoreceptors Rods and cones contain visual pigments (photopigments) Arranged in a stack of disklike infoldings of the plasma membrane that change shape as they absorb light Photoreception: Functional Anatomy of Photoreceptors Functional Rods Rods Functional characteristics Sensitive to dim light and best suited for night vision Rods Rods Functional characteristics Absorb all wavelengths of visible light Rods Rods Functional characteristics Perceived input is in gray tones only Rods Rods Functional characteristics Sum of visual input from many rods feeds into a single ganglion cell Rods Rods Functional characteristics Results in fuzzy and indistinct images Cones Cones Functional characteristics Need bright light for activation (have low sensitivity) Cones Cones Functional characteristics Have pigments that furnish a vivid colored view Cones Cones Functional characteristics Each cone synapses with a single ganglion cell Cones Cones Functional characteristics Vision is detailed and has high resolution Cones Cones Functional characteristics Vision is detailed and has high resolution Cones Cones Functional characteristics Vision is detailed and has high resolution Cones and Rods Cones Chemistry of Visual Pigments Chemistry Retinal is a light­absorbing molecule Combines with opsins to form visual pigments Chemistry of Visual Pigments Chemistry Retinal is a light­ absorbing molecule Similar to and is synthesized from vitamin A Chemistry of Visual Pigments Chemistry Retinal is a light­absorbing molecule Two isomers: 11­cis and Chemistry of Visual Pigments Chemistry Retinal is a light­absorbing molecule Two isomers: 11­cis and all­trans Chemistry of Visual Pigments Chemistry Retinal is a light­ absorbing molecule Two isomers: 11­cis and all­trans Chemistry of Visual Pigments Chemistry Isomerization of retinal initiates electrical impulses in the optic nerve Chemistry of Visual Pigments Chemistry Excitation of Rods Excitation The visual pigment of rods is rhodopsin (opsin + 11­cis retinal) Excitation of Rods Excitation Light phase Rhodopsin breaks down into all­trans retinal + opsin (bleaching of the pigment) Excitation of Rods Excitation Dark phase All­trans retinal converts to 11­cis form Excitation of Rods Excitation Dark phase 11­cis retinal is also formed from vitamin A Excitation of Rods Rods Dark phase 11­cis retinal + opsin regenerate rhodopsin Excitation of Cones Excitation Visual pigments in cones are similar to rods (retinal + opsins) Excitation of Cones Excitation There are three types of cones: blue, green, and red Excitation of Cones Excitation Intermediate colors are perceived by activation of more than one type of cone Excitation of Cones Excitation Method of excitation is similar to rods Phototransduction Phototransduction Light energy splits rhodopsin into all­ trans retinal, releasing activated opsin Phototransduction Phototransduction The freed opsin activates the G protein transducin Phototransduction Phototransduction Transducin catalyzes activation of phosphodiesterase (PDE) Phototransduction Phototransduction PDE hydrolyzes cGMP to GMP and releases it from sodium channels Phototransduction Phototransduction Without bound cGMP, sodium channels close, the membrane hyperpolarizes, and neurotransmitter cannot be released Phototransduction Phototransduction Adaptation Adaptation Adaptation to bright light (going from dark to light) involves: Dramatic decreases in retinal sensitivity – rod function is lost Adaptation Adaptation Adaptation to bright light (going from dark to light) involves: Switching from the rod to the cone system – visual acuity is gained Adaptation Adaptation Adaptation to dark is the reverse Cones stop functioning in low light Adaptation Adaptation Adaptation to dark is the reverse Rhodopsin accumulates in the dark and retinal sensitivity is restored Visual Pathways Visual Axons of retinal ganglion cells form the optic nerve Visual Pathways Visual Medial fibers of the optic nerve decussate at the optic chiasm Visual Pathways Visual Most fibers of the optic tracts continue to the lateral geniculate body of the thalamus Visual Pathways Visual Other optic tract fibers end in superior colliculi (initiating visual reflexes) Visual Pathways Visual Other optic tract fibers end in superior colliculi (initiating visual reflexes) and pretectal nuclei (involved with pupillary reflexes) Visual Pathways Visual Optic radiations travel from the thalamus to the visual cortex Visual Pathways Visual Some nerve fibers send tracts to the midbrain ending in the superior colliculi Visual Pathways Visual A small subset of visual fibers contain melanopsin (circadian pigment) which: Mediates papillary light reflexes Sets daily biorhythms Depth Perception Perception Achieved by both eyesviewing the same image from slightly different angles Gilbert, please point to which animals look closer? Depth Perception Perception Three­dimensional vision results from cortical fusion of the slightly different images Depth Perception Depth If only one eye is used, depth perception is lost and the observer must rely on learned clues to determine depth Retinal Processing: Receptive Fields of Ganglion Cells Fields On­center fields Stimulated by light hitting the center of the field Inhibited by light hitting the periphery of the field Retinal Processing: Receptive Fields of Ganglion Cells Fields Off­center fields have the opposite effects Retinal Processing: Receptive Fields of Ganglion Cells Fields These responses are due to receptor types in the “on” and “off” fields Retinal Processing: Receptive Fields of Ganglion Cells Fields Thalamic Processing Thalamic The lateral geniculate nuclei of the thalamus: Relay information on movement Thalamic Processing Thalamic The lateral geniculate nuclei of the thalamus: Segregate the retinal axons in preparation for depth perception Thalamic Processing Thalamic The lateral geniculate nuclei of the thalamus: Emphasize visual inputs from regions of high cone density Thalamic Processing Thalamic The lateral geniculate nuclei of the thalamus: Sharpen the contrast information received by the retina Cortical Processing Cortical Striate cortex processes Basic dark/bright and contrast information Cortical Processing Cortical Prestriate cortices (association areas) processes Form, color, and movement Cortical Processing Cortical Visual information then proceeds anteriorly to the: Temporal lobe – processes identification of objects Cortical Processing Cortical Visual information then proceeds anteriorly to the: Parietal cortex and postcentral gyrus – processes spatial location The Ear: Hearing and Balance The The three parts of the ear are the inner, outer, and middle ear The Ear: Hearing and Balance The The outer and middle ear are involved with hearing The Ear: Hearing and Balance The The inner ear functions in both hearing and equilibrium The Ear: Hearing and Balance The Receptors for hearing and balance: Respond to separate stimuli Are activated independently The Ear: Hearing and Balance The Outer Ear Outer The auricle (pinna) is composed of: The helix (rim) The lobule (earlobe) Outer Ear Outer External auditory canal Short, curved tube filled with ceruminous glands Outer Ear Outer Tympanic membrane (eardrum) Thin connective tissue membrane that vibrates in response to sound Outer Ear Outer Tympanic membrane (eardrum) Transfers sound energy to the middle ear ossicles Outer Ear Outer Tympanic membrane (eardrum) Boundary between outer and middle ears Middle Ear (Tympanic Cavity) Cavity) A small, air­filled, mucosa­lined cavity Flanked laterally by the eardrum Middle Ear (Tympanic Cavity) Middle A small, air­filled, mucosa­lined cavity Flanked medially by the oval and round windows Middle Ear (Tympanic Cavity) Middle Epitympanic recess – superior portion of the middle ear Middle Ear (Tympanic Cavity) Middle Pharyngotympanic tube – connects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure Middle Ear (Tympanic Cavity) Middle Pharyngotympanic tube – connects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure Middle Ear (Tympanic Cavity) Middle Pharyngotympanic tube – connects the middle ear to the nasopharynx Equalizes pressure in the middle ear cavity with the external air pressure Ear Ossicles Ear The tympanic cavity contains three small bones: the malleus, incus, and stapes Ear Ossicles Ear The tympanic cavity contains three small bones: the malleus, incus, and stapes Ear Ossicles Ear The tympanic cavity contains three small bones: the malleus, incus, and stapes Ear Ossicles Ear The tympanic cavity contains three small bones: the malleus, incus, and stapes Transmit vibratory motion of the eardrum to the oval window Ear Ossicles Ear The tympanic cavity contains three small bones: the malleus, incus, and stapes Dampened by the tensor tympani and stapedius muscles Ear Ossicles Ear The tympanic cavity contains three small bones: the malleus, incus, and stapes Dampened by the tensor tympani and stapedius muscles Ear Ossicles Ear Inner Ear Inner Bony labyrinth Tortuous channels worming their way through the temporal bone Bony labyrinth Inner Ear Inner Contains the vestibule, the cochlea, and the semicircular canals Inner Ear Inner Bony labyrinth Filled with perilymph Inner Ear Inner Bony labyrinth Filled with perilymph Inner Ear Inner Membranous labyrinth Series of membranous sacs within the bony labyrinth Filled with a potassium­ rich fluid Inner Ear Inner The Vestibule The Suspended in its perilymph are two sacs: the saccule and utricle The Vestibule The The central egg­shaped cavity of the bony labyrinth The Vestibule The The saccule extends into the cochlea The Vestibule The The utricle extends into the semicircular canals The Vestibule The These sacs: House equilibrium receptors called maculae Respond to gravity and changes in the position of the head The Vestibule The The Semicircular Canals The Three canals that each define two­thirds of a circle and lie in the three planes of space The Semicircular Canals The Membranous semicircular ducts line each canal and communicate with the utricle The Semicircular Canals The The ampulla is the swollen end of each canal and it houses equilibrium receptors in a region called the crista ampullaris The Semicircular Canals The These receptors respond to angular movements of the head The Semicircular Canals Canals These receptors respond to angular movements of the head The Semicircular Canals The The Cochlea The A spiral, conical, bony chamber that: Extends from the anterior vestibule The Cochlea The A spiral, conical, bony chamber that: Coils around a bony pillar called the modiolus The Cochlea The A spiral, conical, bony chamber that: Coils around a bony pillar called the modiolus The Cochlea The A spiral, conical, bony chamber that: Contains the cochlear duct, which ends at the cochlear apex The Cochlea The A spiral, conical, bony chamber that: Contains the organ of Corti (hearing receptor) The Cochlea The A spiral, conical, bony chamber that: Contains the organ of Corti (hearing receptor) The Cochlea The The cochlea is divided into three chambers: Scala vestibuli The Cochlea The The cochlea is divided into three chambers: Scala vestibuli The Cochlea The The cochlea is divided into three chambers: Scala media The Cochlea The The cochlea is divided into three chambers: Scala media The Cochlea The The cochlea is divided into three chambers: Scala tympani The Cochlea The The cochlea is divided into three chambers: Scala tympani The Cochlea The The scala tympani terminates at the round window The Cochlea The The scalas tympani and vestibuli: Are filled with perilymph The Cochlea The The scalas tympani and vestibuli: Are continuous with each other via the helicotrema The Cochlea Cochlea The scala media is filled with endolymph The Cochlea The The “floor” of the cochlear duct is composed of: The bony spiral lamina The Cochlea The The “floor” of the cochlear duct is composed of: The bony spiral lamina The Cochlea The The “floor” of the cochlear duct is composed of: The basilar membrane, which supports the organ of Corti The Cochlea The The “floor” of the cochlear duct is composed of: The basilar membrane, which supports the organ of Corti The Cochlea The The cochlear branch of nerve VIII runs from the organ of Corti to the brain The Cochlea The The cochlear branch of nerve VIII runs from the organ of Corti to the brain Sound and Mechanisms of Hearing of Sound vibrations beat against the eardrum Sound and Mechanisms of Hearing Hearing Sound vibrations beat against the eardrum Sound and Mechanisms of Hearing Hearing The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows Sound and Mechanisms of Hearing Sound The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows This movement sets up shearing forces that pull on hair cells Sound and Mechanisms of Hearing Sound The eardrum pushes against the ossicles, which presses fluid in the inner ear against the oval and round windows This movement sets up shearing forces that pull on hair cells Sound and Mechanisms of Hearing Hearing Moving hair cells stimulates the cochlear nerve that sends impulses to the brain Properties of Sound Properties Sound is: A pressure disturbance (alternating areas of high and low pressure) originating from a vibrating object Properties of Sound Properties Sound is: Composed of areas of rarefaction and compression Properties of Sound Properties Sound is: Represented by a sine wave in wavelength, frequency, and amplitude Properties of Sound Properties Frequency – the number of waves that pass a given point in a given time Properties of Sound Properties Pitch – perception of different frequencies (we hear from 20–20,000 Hz) Properties of Sound Properties Amplitude – intensity of a sound measured in decibels (dB) Properties of Sound Properties Loudness – subjective interpretation of sound intensity Transmission of Sound to the Inner Ear Transmission The route of sound to the inner ear follows this pathway: Outer ear – pinna, auditory canal, eardrum Transmission of Sound to the Inner Ear Transmission The route of sound to the inner ear follows this pathway: Middle ear – malleus, incus, and stapes to the oval window Transmission of Sound to the Inner Ear Transmission The route of sound to the inner ear follows this pathway: Inner ear – scalas vestibuli and tympani to the cochlear duct Stimulation of the organ of Corti Generation of impulses in the cochlear nerve Transmission of Sound to the Inner Ear Transmission The route of sound to the inner ear follows this pathway: Inner ear – scalas vestibuli and tympani to the cochlear duct Stimulation of the organ of Corti Generation of impulses in the cochlear nerve Transmission of Sound to the Inner Ear Transmission The route of sound to the inner ear follows this pathway: Inner ear – scalas vestibuli and tympani to the cochlear duct Stimulation of the organ of Corti Generation of impulses in the cochlear nerve Transmission of Sound to the Inner Ear Inner Resonance of the Basilar Membrane Membrane Sound waves of low frequency (inaudible): Travel around the helicotrema Resonance of the Basilar Membrane Basilar Sound waves of low frequency (inaudible): Do not excite hair cells Resonance of the Basilar Membrane Membrane Audible sound waves: Penetrate through the cochlear duct Resonance of the Basilar Membrane Resonance Audible sound waves: Vibrate the basilar membrane Resonance of the Basilar Membrane Membrane Audible sound waves: Vibrate the basilar membrane Resonance of the Basilar Membrane Resonance Audible sound waves: Vibrate the basilar membrane Resonance of the Basilar Membrane Resonance Audible sound waves: Excite specific hair cells according to frequency of the sound The Organ of Corti The Is composed of supporting cells and outer and inner hair cells The Organ of Corti The Afferent fibers of the cochlear nerve attach to the base of hair cells The Organ of Corti The The stereocilia (hairs): Protrude into the endolymph The Organ of Corti The The stereocilia (hairs): Touch the tectorial membrane The Organ of Corti The The stereocilia (hairs): Touch the tectorial membrane Excitation of Hair Cells in the Organ of Corti Excitation Bending cilia: Opens mechanically gated ion channels Excitation of Hair Cells in the Organ of Corti Excitation Bending cilia: Causes a graded potential and the release of a neurotransmitter (probably glutamate) Excitation of Hair Cells in the Organ of Corti of The neurotransmitter causes cochlear fibers to transmit impulses to the brain, where sound is perceived Auditory Pathway to the Brain to Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei Auditory Pathway to the Brain Brain From there, impulses are sent to the: Superior olivary nucleus Auditory Pathway to the Brain the From there, impulses are sent to the: Inferior colliculus (auditory reflex center) Auditory Pathway to the Brain to From there, impulses pass to the auditory cortex Auditory Pathway to the Brain Brain Auditory pathways decussate so that both cortices receive input from both ears Auditory Processing Processing Pitch is perceived by: The primary auditory cortex Cochlear nuclei Auditory Processing Auditory Loudness is perceived by: Varying thresholds of cochlear cells The number of cells stimulated Auditory Processing Processing Localization is perceived by superior olivary nuclei that determine sound Deafness Deafness Conduction deafness – something hampers sound conduction to the fluids of the inner ear (e.g., impacted earwax, perforated eardrum, osteosclerosis of the ossicles) Deafness Deafness Sensorineural deafness – results from damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells Deafness Deafness Tinnitus – ringing or clicking sound in the ears in the absence of auditory stimuli Deafness Deafness Meniere’s syndrome – labyrinth disorder that affects the cochlea and the semicircular canals, causing vertigo, nausea, and vomiting Mechanisms of Equilibrium and Orientation Orientation Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule Maintains our orientation and balance in space Mechanisms of Equilibrium and Orientation Orientation Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule Vestibular receptors monitor static equilibrium Mechanisms of Equilibrium and Orientation Orientation Vestibular apparatus – equilibrium receptors in the semicircular canals and vestibule Semicircular canal receptors monitor dynamic equilibrium Anatomy of Maculae Anatomy Maculae are the sensory receptors for static equilibrium Contain supporting cells and hair cells Each hair cell has stereocilia and kinocilium embedded in the otolithic membrane Directional Hair Cells Directional Kinocilia Anatomy of Maculae Anatomy Otolithic membrane – jellylike mass studded with tiny CaCO3 stones called otoliths Anatomy of Maculae Anatomy Utricular hairs respond to horizontal movement Anatomy of Maculae Anatomy Saccular hairs respond to vertical movement Anatomy of Maculae Anatomy Figure 15.35 Effect of Gravity on Utricular Receptor Cells Receptor Otolithic movement in the direction of the kinocilia: Depolarizes vestibular nerve fibers Increases the number of action potentials generated Effect of Gravity on Utricular Receptor Cells Receptor Movement in the opposite direction: Hyperpolarizes vestibular nerve fibers Reduces the rate of impulse propagation Effect of Gravity on Utricular Receptor Cells Receptor From this information, the brain is informed of the changing position of the head Effect of Gravity on Utricular Receptor Cells Receptor Figure 15.36 Crista Ampullaris and Dynamic Equilibrium Equilibrium The crista ampullaris (or crista): Is the receptor for dynamic equilibrium Is located in the ampulla of each semicircular canal Responds to angular movements Crista Ampullaris and Dynamic Equilibrium Equilibrium Each crista has support cells and hair cells that extend into a gel­like mass called the cupula Crista Ampullaris and Dynamic Equilibrium Equilibrium Dendrites of vestibular nerve fibers encircle the base of the hair cells Crista Ampullaris and Dynamic Equilibrium Equilibrium Activating Crista Ampullaris Receptors Receptors Cristae respond to changes in velocity of rotatory movements of the head Activating Crista Ampullaris Receptors Receptors Directional bending of hair cells in the cristae causes: Depolarizations, and rapid impulses reach the brain at a faster rate Activating Crista Ampullaris Receptors Receptors Directional bending of hair cells in the cristae causes: Hyperpolarizations, and fewer impulses reach the brain Activating Crista Ampullaris Receptors Receptors The result is that the brain is informed of rotational movements of the head Rotary Head Movement Rotary Balance and Orientation Pathways Balance There are three modes of input for balance and orientation Vestibular receptors Balance and Orientation Pathways Balance There are three modes of input for balance and orientation Visual receptors Balance and Orientation Pathways Balance There are three modes of input for balance and orientation Somatic receptors Balance and Orientation Pathways Balance These receptors allow our body to respond reflexively Developmental Aspects Developmental All special senses are functional at birth Chemical senses – few problems occur until the fourth decade, when these senses begin to decline Vision – optic vesicles protrude from the diencephalon during the fourth week of development These vesicles indent to form optic cups and their stalks form optic nerves Later, the lens forms from ectoderm Developmental Aspects Developmental Vision is not fully functional at birth Babies are hyperopic, see only gray tones, and eye movements are uncoordinated Depth perception and color vision is well developed by age five and emmetropic eyes are developed by year six With age the lens loses clarity, dilator muscles are less efficient, and visual acuity is drastically decreased by age 70 Developmental Aspects Developmental Ear development begins in the three­week embryo Inner ears develop from otic placodes, which invaginate into the otic pit and otic vesicle The otic vesicle becomes the membranous labyrinth, and the surrounding mesenchyme becomes the bony labyrinth Middle ear structures develop from the pharyngeal pouches The branchial groove develops into outer ear structures ...
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