SPECIAL-SENSES

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Northern Virginia Community College**We aren't endorsed by this school

Course

BIO 101

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Biology

Date

Jan 11, 2025

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C17 THE SPECIAL SENSES1.Sense of touch2.Sense of sight3.Sense of smell4.Sense of hearing5.Sense of tasteOLFACTION: Sense of SMELL-Estimated that humans can recognise about10,000 different odours.-Nose contains that1O million to 100 millionreceptor neuronsfor olfaction, contained within aregion called theolfactory epithelium (found innose/nasal cavity).1.OLFACTORY RECEPTOR CELLS-Each olfactory neuron has receptors forone specific smell.-Olfaction has a direct connection to thebrainslimbic system (emotion centerin our brain).-Unlike other sensory neurons, olfactoryneuron can regenerate throughout aperson’s life2.Supporting cells3.Basal cellsANATOMY AND PATHWAY OF OLFACTIONOLFACTORY GLAND(BOWMAN’S GLAND)Produces mucus tolubricate the olfactoryepitheliumand dissolveodorant-containing gases.(note: smell containingmolecule is “odorant”).OLFACTORY CILIAContainedwithin a layerof mucus,whichdissolvestheodor-containingmoleculesBASAL STEM CELLSTheprogenitororstemcellsfor the regeneratingolfactory epitheliumincase of damageSUPPORTING CELLS(COLUMNAREPITHELIUMLocated in themucousmembrane lining thenose. Used forphysicalsupport,nourishmentandelectrical insulationforolfactory receptor cells.OLFACTORYEPITHELIUMSheet ofneuronsandsupporting cellsthat linesapproximately half of thenasal cavities is used forthetransduction(conversion of chemica linformation into electricalinformation) of odorants.OLFACTORYRECEPTOR CELLSResponds to thechemicalstimulationof anodorantmoleculeby producing agenerator potential, thusinitiating theolfactoryresponse.OLFACTORY NERVE(CN I)Sensory nervethatcarries afferent impulsesfrom theolfactoryreceptor cells.CRIBRIFORM PLATEPerforated byolfactoryforamina,whichallows forthe passageof theolfactory nerves to theroof of the nasal cavity.This conveys informationfrom smell receptors tothe brain.OLFACTORY BULBReceives informationfrom the CN I and send itto theolfactory tracts,itdetects anddiscriminatesodors.OLFACTORY TRACTThis processesolfactorysignalsfromreceptorsneurons, integratesinformation, and relays itto higher brain regions.OLFACTORY CORTEXPortion of thecerebralcortexin thefrontal lobe(bandang noo) that isinvolved in bothprocessingandcodingofolfactory informationHIPPOCAMPUSParts oflimbic system,itflies the odor informationand store itindefinitely.Even decades later, thesame scent can bring thememory and emotionalsalience of the momentflooding backIGS

ODOR THRESHOLD AND ADAPTATION●Olfaction has a low threshold (=sensitivity). Onlya few molecules of certain substances need tobe present in air to be perceived as an odour.●Adaptation (decreasing sensitivity) to odoursoccurs.●Olfactory receptors adapt by about 50% in thefirst second or so after stimulation but adapt veryslowly thereafter.GUSTATION: Sense of TASTE★Taste is a chemical sense, but it is much simplerthan olfaction.★There are only five primary tastes:sour, sweet,bitter, salt,andumami(meaty, savoury flavor)★Flavours other than umami are combinations ofthe other four primary tastes, plusaccompanying olfactory and tactile sensations.ANATOMY AND PATHWAY OF GUSTATIONANATOMY OF TASTE BUDS AND PAPILLAE●Taste budscontain receptors for the sensationof taste.●Approx, 10,000 taste buds are found on thetongue of a young adult and on thesoft palate,pharynxand epiglottis.●Taste buds contains three kinds of epithelialcells;supporting cells; gustatory receptor cellsand basal stem cells.●Taste buds are located in elevations on thetongue calledpapillae.FILIFORM PAPILLAEContainstactile (touch)receptorsbut no tastebuds. They increasefriction between thetongue and food, makingit easier for the tongue tomove food in the oralcavity. Scatteredthroughout the tounge.CIRCUMVALLATEPAPILLAEAn invertedV-shapedrowat the back of thetongue. Each of thesepapillae houses100-300taste budsand areespecially sensitive tobitter and sour taste.FOLIATE PAPILLAELocated in lateraltrenchesof the tongue–most of their taste budsdegenerate in earlychildhood.FUNGIFORM PAPILLAEAremushroom-shapedelevationsscattered overtheentire surfaceof thetongue that contain aboutfive taste budseach.SALIVARY/PAROTIDGLANDSProduces saliva. Salivaacts as a solvent fortaste substances;salivary water dissolvestaste substances, andthe latter diffuse to thetaste receptor sites.GUSTATORYMICROVILLIThin hair-like structuresthat protrude(nasa labasng taste buds) above thetaste buds to capturetastants(tastesubstances) and beprocessed by thegustatory receptor cellsTASTE PORESAn opening from thetaste buds that tastantsenter when captured bythe gustatory microvilliSUPPORTING CELLSPlays a role in clearanceof excessneurotransmitters aftertheir release from tastereceptors cells andsupports the GRC’sfunctions.BASAL CELLSAre considered theprogenitor or stem-cellsfor the gustatory receptorcells.GUSTATORYRECEPTOR CELLSTransduces the tastantsand connect to nervesthat transmit tastesignals to the brain.FACIAL NERVE (CN VII)Carries taste informationfrom the anteriortwo-thirdsof the tongue.IGS

GLOSSOPHARYNGEALNERVE (CN IX)Carries taste informationfrom the posteriorone-third of the tongue.VAGUS NERVE (CN X)Carries taste informationfrom taste buds on theepiglottisand in thethroat.MEDULLA OBLONGATAServes as ahighway intransmitting signalsbetween the spinal cordand the higher parts ofthe brain.PONSTransmit gustatorysignalsbetween theforebrain andcerebellum.THALAMUSActs asrelay station ofall incoming motor andsensory information –hearing, tastem sight andtouch (but not smell) –from the body to thebrain.GUSTATORY CORTEXChief responsibleforperceivinganddistinguishingdifferenttastes called thegustatory cortex. Theterminal connectionserving taste perceptionis located in theanteriorinsulain thetemporallobe andfrontalopercular region.TASTE THRESHOLD AND ADAPTATION➢The threshold for taste varies for each of theprimary tastes.➢The threshold for bitter substances islowest.Becausepoisonous substancesoften are bitter,the low threshold (or high sensitivity) may havea protection function.➢Complete adaptation to a specific taste canoccur in 1-5 minutes of continuous stimulation.VISION●More than half the sensory receptors in thehunan body are located in theEYES.●Large part of the cerebral cortex is devoted toprocessing visual information.●Vision uses visible light that is part of theelectromagnetic spectrum with wavelengthsfrom about400 to 700 nm.●Wavelength is defines as the distance distancebetween two consecutive peaks of anelectromagnetic wave.CONJUNCTIVAAthin, protective mucousmembrane that lines theeyelids and covers thesclera.SCLERAThe white, opaque part ofthe eye that forms theoutermost layer. It ismade up of denseconnective tissue thatprotects the internalcomponents of the eyeand serves as theattachment point for theextraocular muscles thatcontrols eye movement.CORNEATransparent part of theeye that covers the irisand the pupil, it isavascular and is richlysupplied with nerveendings. It plays a crucialrole in focusing light ontothe retina by refracting(bending) light as it entersthe eye.IRISThe colored part of theeye, which surrounds thepupil. It consists ofsmooth muscles thatcontrol its size.CILIARY BODYProduces aqueous humorand contains the ciliarymuscle, which controlsthe shape of the lens forfocusingAQUEOUS HUMORThe clear fluid in theanterior chamber(between the cornea andthe lens). Its maintainsintraocular pressure,provides nutrients to theavascular structures ofthe eye (like the corneaand lens), and removewaste products.IGS

PUPILBlack circular opening inthe center of the iris. Itcontrols the amount oflight that enters the eye yexpanding or contracting.Pupil size changes inresponse to light intensity(constricts in bright lightand dilates in dim light)and emotional orcognitive states.PERRLAPupilsEquallyRound andReactive to lightAccommodationLENSA transparent, biconvexstructure made up ofprotein fibers that focuseslight rays onto the retinato create a clear image. Itchan change its shape toadjust focus for near ordistant objects, a processknown accommodation.VITREOUS HUMORGel-like substance thatfills the space betweenthe lens and the retina. Ithelps maintain the eye’sshape and support theretina in place. It is clearand composed mainly ofwater with traces ofcollagen and hyaluronicacid.CHOROID BODYA layer of blood vesselsbetween the retina andthe sclera that suppliesoxygen and nutrients tothe outer layers of theretina. It contains a highconcentration of melanin,which helps absorbsexcess lights andprevents light fromscattering inside theeyes.RETINALight-sensitive layer oftissue at the back of theeye. It converts light fromthe lens into electricalsignals. Retina containsphotoreceptor cells calledrod(responsible for visionin low light) and cones(responsible for colorvision and detail.OPTIC DISCRound spot on the retinaformed by the passage ofthe axons of the retinalganglion cells, whichtransfer signals from thephotoreceptors of theeyes to the optic nerve(CN II). also known asblind spotsince it lacksphotoreceptors.MACULAThe central part of theretina that allows forhigh-acuity vision,necessary for task likereading and recognizingfacesFOVEA CENTRALISContains a high density ofcone cells and no rodcells, which makes itspecialized from detailed,color vision. It is locatedat the center of themacula, provides theclearest vision.OPTIC NERVEA paired cranial nerve(CN II) that transmitsvisual information fromthe retina to the brain forprocessing.RODS-Responsible for vision in low light conditions(scotopic vision). They allow us to see in dimlight or at night but do not provide color vision.-Extremely sensitive to light; can detect even asingle photon.-Rods cannot detect color; they only perceiveshades of gray (black and white).CONES-Responsible for color vision and visual acuity(sharp, detailed vision). They functions best inbright light (photopic vision) and allows us toperceive a wide range of colors.-Cones can detect colors, and there are threetypes of cones sensitive to different wavelengthsof light;IGS

S-cones : sensitive toshort wavelengths(blue light).M-cones: Sensitive tomedium wavelengths(greenlight).L-cones: Sensitive tolong wavelengths (red lights)IMAGE FORMATION●Light passes through the cornea, the pupil, thelens, and the vitreous humour, and is projectedonto the retina.●Lightrefracts(bends) when it passes through atransparent substance with one density into asecond transparent substances with a differentdensity.●This bending occurs at the junctions of thetwo-substances.Images focused on the retina are inverted andright-to-left reversed due to refraction.●The lens must accommodate to properly focuson the object.●The image is projected onto the central fovea,the site where vision is the sharpest.OPTIC NERVEThe electrical signalsform the photoreceptorsare transmitted to theganglion cells in theretina.OPTIC CHIASMThe optic nerves fromboth eyes meet at theoptic chiasm, a structurelocated at the base of thebrain. Here, fibers formthe nasal (inner) halves ofeach retina cross t0 theopposite side of the brain,this crossing allows visualinformation from the rightvisual field to beprocessed in the lefthemisphere of the brain,and vice versa.OPTIC TRACTSThe nerve fibers continueas the optic tracts whichcarries visual informationfrom the opposite visualfield.LATERAL GENICULATENUCLEUS OF THETHALAMUSThe optic tracts project toth elateral geniculatenucleus, a relay station inthe thalamus. The LGNprocesses and organizesthe visual informationbefore sending it to thevisual cortexOPTIC RADIATIONSFrom the LGN, visualsignals travel through theoptic radiations which arepathways that carry theinformation to differentparts of the visual cortex.PRIMARY VISUALCORTEXLocated in theOccipitallobeof the brain. This iswhere the brain begins tointerpret the basicfeatures of the visualinformation, such aslights, shape,andmovement.HEARING AND EQUILIBRIUM●The transduction of sound vibrations by the ears’sensory receptors intro electrical signals is 1000times faster than the response to light by theeyes’ photoreceptors.●The ear also contains receptors forequilibrium.●The ear is divided into three groupsthe externalear, middle ear, and internal ear.PINNA (AURICLE)The visible part of th earmade of cartilage andskin. It has a uniqueshape that helpts togather sound waves fromthe environment andfunnel them into the eatcanaEAR CANALSa tube-like structure thatruns from the pinna to theeardrum. It is lined withtiny ears and glands thatproduces earwax(cerumen), which helps totrap dust and otherIGS

foreign particles.TYMPANIC MEMBRANE(EARDRUM)Thin membrane thatseparates the externalear from the middle ear. Itvibrates when soundwaves hit it, convertingsound energy into themechanical vibration.OSSICLES●Malleus(hammer);attached to theeardrum, itreceivedvibrations fromthe tympanicmembrane.●Incus(Anvil)positionedbetween themalleus and thestapes, it acts asa bridge,transferringvibrations fromthe malleus to thestapes.●Stapes(stirrup):the smallest bonein the humanbody, it connectsto the ovalwindow of theinner ear. Itamplifies andtransmits thesound vibrationsinto the inner ear.EUSTACHIAN TUBEA tube that connectsmiddle ear to the throat. Ithelps to equalizepressure on both sides ofthe eardrum, which isessential for properhearing and preventsdamage to the eardrumfrom sudden pressurechanges.COCHLEAA spiral-shaped,fluid-filled structure thatplays a crucial role in tothe process of hearing. Itconstraints basilar haircells. That convert soundvibrations intro electricalsignals, which are thentransmitted to the brainvia the auditory nerve.VESTIBULAR SYSTEMThe part of the inner earresponsible formaintaining balance andspatial orientation thatconsists of semi-circularcanals and vestibule.●SEMICIRCULARCANALS:threeloop-shapedstructurespositions at rightangles to eachother. Theydetect rotationalmovements of thehead.●VESTIBULE:central part of thebony labyrinththat contains twosacs, theUTRICLEand theSACCULE.These structuresdetects linearmovements.VESTIBULOCOCHLEARNERVE (CN VIII)VESTIBULAR NERVE:relays information to thebrain related to motion,equilibrium and position.COCHLEAR NERVE:Transfers auditoryinformation from thecochlea to the brain.NATURE OF SOUND●Sound waves are alternating high andlow-pressure regions travelling in the samedirection through medium●The frequency of a sound vibration is its pitch.The higher the frequency of vibration, the higherthe pitch.●The sounds heard most acutely by the humanear are those from sources that vibrate atfrequencies between500 and 5000 hertz.●Sound intensity is measured in units calleddecibels (dB).THE EQUILIBRIUM➔TheCEREBELLUMprocesses information fromthe vestibular system.IGS

➔Equilibrium (balance) exist in two forms:1.STATIC EQUILIBRIUM:maintenance of thebody’s position relative to the force of gravity.2.DYNAMIC EQUILIBRIUM:maintenance of thebody’s position in response to suddenmovements.THE AUDITORY PATHWAY TO THE BRAINCOCHLEAR NERVEThe electrical signalstravel from the hair cellsthrough the auditorynerve to the brainstem(cochlear nuclei)BRAINSTEM(COCHLEAR NUCLEI)Serves as a relay stationto be processed in thehigher brain centers.SUPERIOR OLIVARYCOMPLEXThe signals pass to thesuperior olivary complexlocated in the PONS,which helps with soundlocalization by comparingthe timing and intensity ofthe sounds reaching bothears.INFERIOR COLLICULUSIntegrated the auditoryinformation andcoordinates reflexiveresponse to sound.THALAMUS (MEDIALGENICULATE)The auditory signals arethen relayed to thethalamus, specifically themedial geniculate body,which acts as a relaystation for sensoryinformation.PRIMARY AUDITORYCORTEXThe signals reach theprimary auditory cortexlocated in thetemporallobeof the brain. This iswhere the brain interpretsand processes the soundinformation, allowing usto recognize andunderstand sounds,speech, and music.AGEING AND THE SPECIAL SENSES-Smell and taste are not affected by ageing untilaround age50.-This is due to gradual loss of olfactory receptorcells and gustatory receptor cells coupled withtheir slower rate of replacement as we age.-The lens loses some of its elasticity and thuscannot change shape as easily, resulting inpresbyopia (farsightedness)/-By about age 60, around 25% of individualsexperience a noticeable hearing loss, especiallyfor higher pitched sounds.IGS