MCB 244: Chapter 17
MCB 244: Chapter 17 MCB 244
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This 16 page Class Notes was uploaded by Laura Kunigonis on Monday December 7, 2015. The Class Notes belongs to MCB 244 at University of Illinois at Urbana-Champaign taught by Dr, Chester Brown in Fall 2015. Since its upload, it has received 19 views. For similar materials see Human Anatomy and Physiology I in Biology at University of Illinois at Urbana-Champaign.
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Chapter 17 Five Special Senses Olfaction Gustation Vision Equilibrium Heanng What distinguishes the five special senses from somatic senses The receptors for the special senses are housed in specialized organs instead of being dispersed throughout the body information from them is carried by special afferents as opposed to general somatic and visceral afferents Where are the olfactory organs located Within the olfactory epithelium in nasal cavity On either side of the nasal septum Inferior surface of cribriform plate and superior nasal cochae see fig 173 What type of cells make up the two layers of the olfactory organs Olfactory Epithelium Lamina Propia Olfactory Epithelium One of two layers of the olfactory organs Olfactory receptor neurons chemoreceptors Basal cells stem cells that replace olfactory receptors every 60 days Supporting cells simple columnar epithelium Basal cells Olfactory stem cells that replace receptors every 60 days Lamina Propia One of two layers of the olfactory organs contains olfactory glands that secrete mucus Olfactory Receptor Cells Highly modified bipolar neurons Apart of the olfactory epithelium detect dissolved chemicals interacting with odarantbinding proteins humans have gt900 different odorant binding proteins How can humans distinguish 4000 different odors if we only have 900 different genes encolding odorantbinding proteins Olfactory epithelium contains receptor populations with distinct sensitivities The CNS interprets each smell on the basis of overall pattern of receptor activity Central Adaptation Ensures that you quickly lose awareness to a smell that you have been exposed to for some timebut retain sensitivity to others Olfactory Signal Transduction Pathway Odorant bind to receptors in dendrites Binding activates Gprotein coupled receptor GProtein coupled receptor activates adenylate cyclase to simulate cAMP production cAMP binds to sodium channels causing their opening and membrane depolarization Axons leaving the olfactory epithelium collect into bundles of 20 or more and synapse in the olfactory bulb Axons leave the olfactory bulb via the olfactory tract From there the signal reaches the olfactory cortex temporal lobe of the cerebrum and hypothalamus parts of the limbic system which elicit emotionalmemory response to odors What is unique about olfaction as compared to other special senses does not synapse in the thalamus Special senses that transmit info to hypothalamus and limbic system Func onalconsequences Olfaction Gustation Elicit emotional responses memories can also trigger reflexes such as stimulating digestive activity Special senses that have stem cells for continual replacement of damaged receptors Both olfaction and gustation contain Basal Cells Water Receptors Associated with pharynx and circumvallate papillae Lingual Papillae also how many taste buds each and location Specific epithelial projections of superior tongue where taste buds cluster 3 types Filiform Papillae no taste buds Purpose is to provide friction towards front of tongue Fungiform Papillae 5 taste buds each middle of tongue Circumvallate Papillae 100 taste bus each back of tongue 4 primary tastes and 2 additional primary sweet sugars alcohols some amino acids salty bitter alkaloids sour acids addMonak umamisavory free glutamates water receptor Umami Savory taste Detect free glutamates important because these are the most abundant amino acids in our bodies Gustatory Transduction differences in tastes Salt and sour Activate chemically gated ion channels resulting in cell repolarization sweet bitter and umami Activate Gprotein gustducins coupled receptors Gustation signaling pathway Information is passed from medulla oblongata to the thalamus for screening Sensory afferents synapse in the thalamus then routed to Gustatory cortex in the insula of the cerebrum and Hypothalamus and limbic system to elicit emotional reaction to taste Lacrimal Caruncle Associated with eyelids Contain sebaceous and sudoriferous glands that produce secretions to lubricate the eye surface Tarsal Glands Associated with eyelashes Modified sebaceous glands that produce oily secretion to prevent lid stickings Conjunctiva Transparent mucous membrane Covers anterior surface of eye and interior surface of lids Produces lubricating mucus to keep eyes moist Contains tiny capilaries Lacrimal Apparatus Lateral and superior to eye Produces lacrimal fluid to cleanse and protect eye surface Lacrimal fluid contains Mucus lubrication Antibodies immune defense against microbes Lysozyme enzyme that yses bacteria Palpebrae eyeHds continuation of skin Palpebral fissure gap that separates upper and lower papebrae Canthus where eyelids connect Lacrimal Canaliculi Where lacrimal fluid is collected medial corner of eye 3 layers of the wall of the eye Outer Fibrous Tunic Intermediate Vascular Tunic lnner Neural Tunic Fibrous Tunic Outer layer of the wall of eye Avascular dense fibrous connective tissue includes Sclera white of eye Cornea Sclera White of the eye Posterior 56ths Function maintain eye shape attachment of eye muscles Continuous with epineurium of optic nerve Cornea Anterior 16 Clear allows light to enter eye high concentration of pain receptors Damagescaring inhibit vision Corneal transplants No tissue match required Vascular Tunic Uvea Middle layer of wall of eye Route for blood vessels and lymphatic vessels Regulates amount of light entering eye Secretes and reabsorbs humor that circulates within chamber of eye Controls shape of lens Components lris Ciliary Body The Choroid Iris Anterior portion of uvea Contains Papillary constrictor muscles Consists of smooth muscle elastic fibers Eye color determined by melanin density and distrubution Parasympathetic stimulation Pupillary constrictor muscles Series of concentric circles around the pupil Used to decrease pupil diameter Sympathetic stimulation pupillary dilator muscles Extend radially away from edge of pupil lncrease pupil diameter Ciliary Body Contain ciliary processes and muscles that attach to suspensory ligaments of lens circular smooth muscles function to focus lens and center it posterior to pupil Secretes fluid that fills anterior of eye Choroid Vascular layer Separates fibrous and neural tunics Contains melanocytes to prevent light scatter melanocytes Component of the Choroid Prevent light scatter Neural Tunic lnner layer of wall of eye Pigmented part thin outer Neural partinner retina Pigmented Part Portion of Neural tunic Melaninrich simple cuboidal epithelium Absorbs light to prevent visual echos stores vitamin A Neural Part Part of Neural Tunic Contains visual receptors Rods and Cones and associated Neurons Rod Photoreceptors Do not discriminate colors but are highly sensitive to light Long and slender Respond to almost any photon 130 million Around periphery of retina As you move towards the center of the retina the density of rods gradually increase Undergo extensive convergence in retina vision is grainy and blurry Cone Photoreceptors Provide color vision 3 types Densely clustered in fovea center of macula lutea short and tapered 6 million concentrated at macula Show little convergence to their ganglion cells P cells Bipolar cells Within Retina Transmit info from rods cones also synapse with ganglion cells Horizontal Cells Involved in visual processing Extend across outer portion of retina Synapse with photoreceptors and bipolar cells modulate communication between photoreceptors and ganglion cells thereby altering sensitivity Amacrine Cells Comparable to horizontal cell layer Found where bipolar cells synapse with ganglion cells modulate communication between photoreceptors and ganglion cells thereby altering sensitivity Ganglion Cells Transmit visual information to brain axons exit eye as optic optic nerve Optic disc blind spot circular region just medial to fovea where axons bundle to form the optic nerve Scotomas Abnormal blind spots outside of region of the optic disc damage Macula Lutea Focal point directly behind center of lens Contains most of the cones of the retina Fovea centralis Center of Macula cones only Posterior Cavity Posterior to lens Filled with vitreous humor Func ons Support retina in contact with choroid while allowing light to pass Provide lntraocular pressure to counteract extrinsic eye muscles Vitreous humor Clear gel formed in embryo Maintained throughout life Fills Posterior eye cavity Anterior Cavity Anterior to lens Filled with Aqueous Humor Aqueous Humor Diffuses through both cavities Reabsorbed at the canal of Schlemm at base of iris Func on Maintain consistent intraocular pressue Diffusion medium for lens and cornea Canal of Schlemm At base of iris Reabsorbs Aqueous humor Glaucoma Failure to drain aqueous humor Pressure compresses retina and optic nerve resulting in vision loss The Lens Transparent flexible avascular disc Cells have no organelles Cells contain crystallin proteins that last a lifetime Held in place directly behind pupil by suspensory ligaments which attaches lens to ciliary body Cataract Clouding of the lens due to clumping of crystallins Structures that refract light Cornea lens humors Accomodation Shape of lens changes to focus image on retina Mediated by Parasympathetic system Distant objects lens is flattened Close objects lens shape becomes more rounded Myopia nearsightedness Focal point is in front of retina Cannot focus on distant objects Corrected with concave lens Hyperopia Focal point is behind retina Cannot focus on close objects Corrected with convex lens Presbyopia Agerelated loss in near vision accommodation Due to decrease in lens elasticity Corrected with reading glasses Astigmatism Unequal curvature of cornea or lens Part out of focus part in focus Visual Acuity Level of detail seen at a distance of 20ft A person standing at 20ft with 20x vision would have the visual acuity of a normal person at x feet 2020 normal 2015 Person standing at 20ft can see what normal people can see at 15ft 20200 legally blind Signal Transduction Pathway for Photoreception A rhodopsin molecule binds a photon Retinal is isomerized from 11cis to 11trans activating and releasing opsin Opsin activates the GProtein transducin Transducin activates phosphodiesterase PDE PDE breaks down cGMP which CLOSES Na channels This reduces the dark current This reduces neurotransmitter release and hyperpolarizes the receptor The change in activity is relayed to bipolar cells to ganglion cells and down the optic nerve to 1 Suprachiasmatic Nucleus circadian rhythm 2 Superior colliculus visual reflex 3 Primary visual cortex Bleaching After absorbing a photon the rhodopsin molecule begins to break down into retinal and opsin Optic Radiation Bundle of projection fibers linking lateral geniculate with visual cortex External Ear Auricle pinna External acoustic meatus Tympanic membrane Auricle pinna Surrounds entrance to external acousitc meatus Protects opening of canal Funnels sound and provides directional sensitivity External acoustic Meatus Ends at tympanic membrane Lined with hairs and ceruminous glands Tympanic membrane Thin semitransparent sheet of connective tissue and epithelium The middle ear tympanic cavity Airfilled mucosalined chamber between tympanic membrane and oval window Encloses three auditory Ossicles Malleus lncus Stapes Auditory ossicles Malleus lncus Stapes Amplify and transmit sound energy from tympanic membrane to oval window Tensor tympani and stapedius muscles Protect ears from loud sounds by inhibiting vibrations of tympanic and oval windows Innerear located in temporal bone posterior to eye consists of network of fluid fluid filled chambers Fluid functions to transit sound or movement energy to mechanorecptor cells Vestibule gravity and acceleration Semicircular Canals rotation Cochlea sound Vestibule gravity and acceleration Component of inner ear Membranous sacs saccule and utricle Semicircular Canals rotation 3 in total xyz planes Connected to vestibule Filled with endolymph are semicircular ducts and semicircular canals the same Each duct contains Ampulla with gelatinous cupula Stereocilia resemble long microvilli on the surface of hair cells Kinocilium Single large cilium Endolymph Liquid in Semircular canals Cochlea Sound Spiral conical chamber begins at oval window contains organ of corti filled with perilymph Perilymph Liquid in cochlea Hair Cells Basic receptors of inner ear Provide info about direction and strength of mechanical stimuli Utricle and Saccule Provide Equilibrium Sensations Connected with endolymphatic duct which ends in endolymphatic sac Maculae Oval structures where hair cells cluster Statoconia Densely packed calcium carbonate crystals on surface of gelatinous mass Makes up Otolith ear stone When head is level statoconia39s weigh presses on macular surface pushing the hair cell processes down When head is tilted the pull of gravity on the statoconia shifts them to the side thereby distorting the hair cell processes Otolth Ear stone Gelatinous matrix and statoconia Vestibular Receptors Active sensory neurons of vestibular ganglia Axons form vestibular branch of vestibulocochlear nerve Synapse within vestibular nuclei Four Functions of Vestibular Nuclei 1 Integrate sensory info about balance from both sides of head 2 Relay info from vestibular complex to cerebellum 3 Relay info from vestibular complex to cerebral cortex 4 Send commands to motor nuclei in brain stem and spinal cord Stereocilia Within semicircular ducts Resemble long microvilli Are on surface of hair cells Kinocilium within semicircular ducts Single large cilium What sensory information is encoded for by hair cells in the semicircular ducts Provide information about direction and strength of mechanical stimuli Ampulla An expanded region of the semicircular ducts which contains sensory receptors Contains a region in the wall called the Crista Region in the ampulla that contains the receptors hair cells Crista Region in the ampulla that contains the receptors Each crista is bound to a cupula Gelataneous structure which extends the full width of the ampulla Cupula Gelatanious structure which extends the full width of the ampulla During head rotation movement of endolymph along the side of the semicircular duct pushes cupula to the side and distorts the receptor process Movement of fluid in one direction stimulates the hair cells stereocilia displaced toward kinocilium Movement of Endolymph stimulates hair cells in one direction and inhibits hair cells in the other direction When stereocilia are displaced toward kinocilium Hair cells stimulated When stereocilia are displaced away from kinocilium Hair cells inhibited General Mechanism of Hearing Sound waves in the air enter the external auditory canal Vibrate the tympanic membrane This in turn vibrates the malleus incus and stapes This creates pressure waves through the oval window into the perilymph of the scala vestibuli of the cochlea Pressure waves distort the basilar membrane on their way to the round window of the scala tympani causing hair cell cilia to brush against the tectorial membrane and become distorted Flexion of the stereocilia opens ion channels causing depolarization of stimulated hair cells An EPSP is transmitted to the sensory neurons of the spiral ganglion Axons of the spiral ganglion transmit action potentials along the vestibulocochlear nerve to be diverged to the inferior colliluli of the mesencephalon to initiate auditory reflexes to the thalamus for screening and routing to the auditory cortex in the temporal lobe of the cerebrum for interpretation Pitch Determined by region of basilar membrane vibrated Low frequency sounds travel further into the cochlea APEX High frequency sounds stimulate Base Volume Volume is determined by the number of hair cells stimulated High volume stimulates more hair cells Effects of Aging on the Ear Tympanic membrane gets less flexible Articulations between ossicles stiffens Round window may begin to ossify