Introduction - The University of Alabama at Birmingham | UAB



IntroductionEvery plasmalemma functions as a receptor for the cellPlasmalemma has receptors specific for:Chemical stimuliElectrical stimuliMechanical stimuliNot all plasmalemmae have the same receptor sitesIntroductionSensory information arrives at the CNSInformation is “picked up” by sensory receptorsSensory receptors are the interface between the nervous system and the internal and external environmentIntroductionCategories of SensesGeneral sensesRefers to temperature, pain, touch, pressure, vibration, and proprioceptionSpecial sensesRefers to smell, taste, balance, hearing, and visionSpecial sense receptors are located in complex sense organsExamples are: eyes, ears, and taste budsReceptorsEach receptor has a characteristic sensitivityThis leads to receptor specificitySpecificity is due to the structure of the receptorReceptorsExamples of SpecificityFree nerve endings are the simplest receptorsThese respond to a variety of stimuliReceptors of the retina Very specific and only respond to lightThe area monitored by the receptor cell is the receptive fieldReceptorsReceptive FieldsLarge receptive fields have receptors spread far apart, which makes it difficult to localize a stimulusSmall receptive fields have receptors close together, which makes it easy to localize a stimulusReceptorsInterpretation of Sensory InformationInformation is relayed from the receptor to a specific neuron in the CNSEach pathway carries information concerning a specific sensationThe identity of the active neuron indicates:Location of the stimulusNature of the stimulusInterpretation of Sensory InformationClassification of ReceptorsTonic receptorsAlways activePhotoreceptors of the eye and receptors that constantly monitor body positionPhasic receptorsNormally inactive but become active when necessary (for short periods of time)Touch and pressure receptors of the skin (for example)ReceptorsCentral Processing and AdaptationAdaptationReduction in sensitivity due to a constant stimulusPeripheral adaptationReceptors respond strongly at first and then declineCentral adaptationAdaptation within the CNSConsciously aware of a stimulus, which quickly disappearsThe General SensesClassification of the General SensesOne classification scheme:ExteroceptorsProvide information about the external environmentProprioceptorsProvide information about the position of the bodyInteroceptorsProvide information about the inside of the bodyThe General SensesClassification of the General SensesAnother classification scheme:NociceptorsRespond to the sensation of painThermoreceptorsRespond to changes in temperatureMechanoreceptorsActivated by physical distortion of cell membranes ChemoreceptorsMonitor the chemical composition of body fluidsThe General SensesNociceptors Known as pain receptorsAssociated with free nerve endings and large receptor fieldsThis makes it difficult to “pinpoint” the location of the origin of the painThere are three typesReceptors sensitive to extreme temperaturesReceptors sensitive to mechanical damageReceptors sensitive to chemicalsThe General SensesNociceptors Fast painSensations reach the CNS fastAssociated with pricking pain or cutsSlow painSensations reach the CNS slowlyAssociated with burns or aching painsReferred painSensations reach the spinal cord via the dorsal rootsSome visceral organ pain sensations may reach the spinal cord via the same dorsal rootThe General SensesThermoreceptors Found in the dermis, skeletal muscles, liver, and hypothalamusCold receptors are more numerous than hot receptorsExist as free nerve endingsThese are phasic receptorsThese are very active when the temperature changes, but quickly adapt to a stable temperatureThe General SensesMechanoreceptorsReceptors that are sensitive to stretch, compression, twisting, or distortion of the plasmalemmaeThere are three typesTactile receptorsBaroreceptorsProprioceptorsThe General SensesMechanoreceptorsTactile receptorsProvide sensations of touch, pressure, and vibrationsUnencapsulated tactile receptorsFree nerve endings, tactile disc, and root hair plexusEncapsulated tactile receptorsTactile corpuscle, Ruffini corpuscle, and lamellated corpuscleThe General SensesMechanoreceptorsUnencapsulated tactile receptorsFree nerve endings are common in the dermisTactile discs are in the stratum basale layerRoot hair plexus monitors distortions and movements of the body surfaceThe General SensesMechanoreceptorsEncapsulated tactile receptorsTactile corpuscleCommon on eyelids, lips, fingertips, nipples, and genitaliaRuffini corpuscleIn the dermis, sensitive to pressure and distortionLamellated corpuscleConsists of concentric cellular layers / sensitive to vibrationsThe General SensesMechanoreceptorsBaroreceptorsStretch receptors that monitor changes in the stretch of organsLocation:StomachSmall intestineUrinary bladderCarotid arteryLungsLarge intestineThe General SensesMechanoreceptorsProprioceptorsMonitor the position of jointsMonitor tension in the tendons and ligamentsGolgi tendon organs are the receptors in the tendonsMonitor the length of muscle fibers upon contractionMuscle spindles are receptors in the musclesThe General SensesChemoreceptorsDetect small changes in the concentration of chemicalsRespond to water-soluble or lipid-soluble compoundsFound in respiratory centers of the:Medulla oblongataCarotid arteriesAortic archOlfaction (Smell)OlfactionThe olfactory epithelium consists of:Olfactory receptorsSupporting cellsBasal cellsOlfactory glandsOlfaction (Smell)Olfactory PathwaysAxons leave the olfactory epitheliumPass through the cribriform foraminaSynapse on neurons in the olfactory bulbsImpulses travel to the brain via CN IArrive at the cerebral cortex, hypothalamus, and limbic systemOlfaction (Smell)Olfactory DiscriminationThe epithelial receptors have different sensitivities and we therefore “detect” different smellsOlfactory receptors can be replacedThe replacement activity declines with ageGustation (Taste)Gustation The tongue consists of papillaePapillae consist of taste budsThere are three types of papillaeFiliformFungiformCircumvallate Taste buds consist of gustatory cellsGustation (Taste)Gustatory ReceptorsTaste buds consist of gustatory cellsEach gustatory cell has a slender microvilli that extends through the taste pore into the surrounding fluidDissolved chemicals contact the microvilliThis provides a stimulus that changes the transmembrane potential of the gustatory cellInformation goes to the brain for the interpretation of tasteGustation (Taste)Gustatory PathwaysDissolved chemicals contact the taste hairs (microvilli)Impulses go from the gustatory cell through CN VII, IX, and XSynapse in the nucleus solitarius of the medulla oblongataSynapse in the medial lemniscusSynapse in the thalamusInformation arrives at the gustatory cortexGustation (Taste)Gustatory DiscriminationWe begin life with more than 10,000 taste budsThe number declines rapidly by age 50Coupled with the decline in olfactory receptors, taste diminishes as we ageThreshold level is low for gustatory cells responsible for unpleasant stimuliThreshold level is high for gustatory cells responsible for pleasant stimuliGustation (Taste)Gustatory DiscriminationThe are four (possibly six) primary tastes sensationsSweetSaltySourBitterUmamiTaste that is characteristic of beef and chicken brothWater Located mainly in the pharynx regionEquilibrium and HearingEquilibrium and HearingStructures of the ear are involved in balance and hearingThe ear is subdivided into three regionsExternal earMiddle earInner earEquilibrium and HearingThe External EarConsists of:Auricle (pinna)External acoustic meatusTympanic membraneCeruminous glandsProduces cerumen (earwax)Equilibrium and HearingThe Middle EarConsists of:Tympanic cavityAuditory ossiclesMalleus, incus, and stapesAuditory tube (pharyngotympanic tube)Muscles:Tensor tympaniStapediusEquilibrium and HearingThe Inner EarConsists of:Receptors housed in membranous labyrinth (within the bony labyrinth)Bony labyrinthVestibuleSemicircular canalsCochleaUtricleSacculeEquilibrium and HearingThe Vestibular Complex and EquilibriumThe vestibular complex is the part of inner ear that provides equilibrium sensations by detecting rotation, gravity, and accelerationConsists of:Semicircular canalsUtricleSacculeEquilibrium and HearingThe Vestibular Complex and EquilibriumThe semicircular canalsEach semicircular canal encases a ductThe beginning of each duct is the ampullaWithin each ampulla is a crista with hair cellsEach hair cell contains a kinocilium and stereociliaThese are embedded in gelatinous material called the cupulaThe movement of the body causes movement of fluid in the canal, which in turn causes movement of the cupula and hair cells, which the brain detectsEquilibrium and HearingThe Vestibular Complex and EquilibriumWhen you rotate your head:The endolymph in the semicircular canals begins to moveThis causes the bending of the kinocilium and stereociliaThis bending causes depolarization of the associated sensory nerveEquilibrium and HearingThe Vestibular Complex and EquilibriumWhen you rotate your head:When you rotate your head to the right, the hair cells are bending to the left (due to movement of the endolymph)When you move in a circle and then stop abruptly, the endolymph moves back and forth causing the hair cells to bend back and forth resulting in confusing signals, thus dizzinessEquilibrium and HearingThe Vestibular Complex and EquilibriumThe utricle and sacculeThe utricle and saccule are connected to the ampulla and to each other and to the fluid within the cochleaHair cells of the utricle and saccule are in clusters called maculaeHair cells are embedded in gelatinous material consisting of statoconia (calcium carbonate crystals)Gelatinous material and statoconia collectively are called an otolithEquilibrium and HearingThe Vestibular Complex and EquilibriumWhen you move up or down (elevator movement):Otoliths rest on top of the maculaeWhen moving upward, the otoliths press down on the macular surfaceWhen moving downward, the otoliths lift off the macular surfaceWhen you tilt side to side:When tilting to one side, the otoliths shift to one side of the macular surfaceEquilibrium and HearingPathways for Vestibular SensationsSensory fibers form the vestibular branch of the vestibulocochlear nerveSynapse within the vestibular nucleiLocated between the pons and medulla oblongataEquilibrium and HearingPathways for Vestibular SensationsThe vestibular nuclei:Integrate sensory information from each side of the headSends information to:CerebellumCerebral cortexMotor nuclei within the brain stem and spinal cordCranial nerves involved are:III, IV, VI, and XIEquilibrium and HearingHearingThe cochlea:Consists of “snail-shaped” spiralsSpirals coil around a central area called the modiolusWithin the modiolus are sensory neuronsThe sensory neurons are associated with CN VIIIOrgan of CortiEquilibrium and HearingThe Cochlea (continued)Each spiral consists of three layersScala vestibuli (vestibular duct): consists of perilymphScala tympani (tympanic duct): consists of perilymphScala media (cochlear duct): consists of endolymph / this layer is between the scala vestibuli and scala tympaniEquilibrium and HearingThe Cochlea (continued)There is a basilar membrane between each layerThe scala vestibuli and scala tympani are connected at the apical end of the cochleaSense organs rest on the basilar membrane within the scala mediaEquilibrium and HearingThe CochleaThe Organ of CortiAlso known as the spiral organRests on the basilar membrane between the scala media and the scala tympaniHair cells are in contact with an overlying tectorial membraneThis membrane is attached to the lining of the scala mediaSound waves ultimately cause a distortion of the tectorial membrane, thus stimulating the organ of CortiEquilibrium and HearingSound DetectionSound waves enter the external acoustic meatusThe tympanic membrane vibratesCauses the vibration of the ossiclesThe stapes vibrates against the oval window of the scala tympaniPerilymph begins to moveEquilibrium and HearingSound DetectionAs the perilymph moves:Pressure is put on the scala mediaThis pressure distorts the hair cells of the organ of CortiThis distortion depolarizes the neuronsNerve signals are sent to the brain via CN VIIIEquilibrium and HearingAuditory PathwaysStimulation of hair cells in the cochleaSensory neurons carry the sound information from N VIII to the cochlear nucleiInformation travels to the inferior colliculi of the midbrainEquilibrium and HearingAuditory Pathways (continued)The inferior colliculi causes the rotation of the head in the direction of the soundInformation goes to the medial geniculate nucleusInformation goes to the auditory cortex of the temporal lobeVisionAccessory Structures of the EyePalpebrae (eyelids)Medial and lateral canthusConnect the eyelids at the corners of the eyePalpebral fissure Area between the eyelidEyelashes Contain root hair plexus, which triggers the blinking reflexVisionAccessory Structures of the Eye (continued)ConjunctivaEpithelial lining of the eyelidGlandsGlands of Zeis, tarsal glands, lacrimal gland, lacrimal caruncleVisionAccessory Structures of the EyeEyelidsAlso known as palpebraeConnected at the corners called medial and lateral canthusEyelashes are along the palpebral bordersEyelashes are associated with sebaceous glandsTarsal glands are located along the inner lining of the eyelidsThey secrete lipid products that prevent the eyelids from sticking togetherVisionAccessory Structures of the EyeEyelidsConjunctivaCovers the inside lining of the eyelids and the outside lining of the eyeFluid production helps prevent these layers from becoming dryPalpebral conjunctiva (Inner lining of the eyelids)Ocular conjunctiva (Outer lining of the eyelids)VisionAccessory Structures of the EyeEyelidsAll of the glands are for protection or lubricationGlands of Zeis: sebaceous glands / associated with eyelashesTarsal glands: secrete a lipid-rich product / keeps the eyelids from sticking together / located along the inner margin of the eyelidsLacrimal glands: produce tears / located at the superior, lateral portion of the eyeLacrimal caruncle glands: produce thick secretions / located within the canthus areasVisionAccessory Structures of the Eye EyelidsAn infection of the tarsal gland may result in a cystAn infection of any of the other glands may result in a styVisionAccessory Structures of the EyeThe Lacrimal ApparatusProduces, distributes, and removes tearsThe lacrimal apparatus consists of:Lacrimal glands (produce tears)Lacrimal canaliculiLacrimal sacNasolacrimal ductVisionAccessory Structures of the Eye The Lacrimal ApparatusTears are produced by the lacrimal glandsFlow over the ocular surfaceFlow into the nasolacrimal canal (foramen)This foramen enters into the nasal cavityTherefore, when you sob heavily, tears flow across your eye and down your face and also through the nasolacrimal canal into your nose and out, resulting in a “runny” noseVisionThe EyeConsist of:ScleraCorneaPupilIrisLensAnterior cavityPosterior cavityThree tunics: (1) fibrous tunic, (2) vascular tunic, and (3) neural tunicRetinaVisionThe EyesThe Fibrous Tunic (outermost layer)Makes up the sclera and corneaThe cornea is modified scleraProvides some degree of protectionProvides attachment sites for extra-ocular musclesContains structures associated with focusingVisionThe EyesThe Vascular Tunic (middle layer)Consists of blood vessels, lymphatics, and intrinsic eye musclesRegulates the amount of light entering the eyeSecretes and reabsorbs aqueous fluid (aqueous humor)Controls the shape of the lensIncludes the iris, ciliary body, and the choroidVisionThe EyesThe Vascular Tunic The irisConsists of blood vessels, pigment, and smooth musclesThe pigment creates the color of the eyeThe smooth muscles contract to change the diameter of the pupilVisionThe EyesThe Vascular Tunic The ciliary bodyThe ciliary bodies consist of ciliary muscles connected to suspensory ligaments, which are connected to the lensThe choroid Highly vascularizedThe innermost portion of the choroid attaches to the outermost portion of the retinaVisionThe EyesThe Neural Tunic (inner layer)Also called the retinaMade of two layersPigmented layer—outer layerNeural layer—inner layerRetina cellsRods (night vision) Cones (color vision)VisionThe EyesThe Neural Tunic (inner layer)Retinal organizationThere are rods and cones all over the retina100% cones in the fovea centralis areaThe best color vision is when an object is focused on the fovea centralis0% rods or cones in the optic disc areaIf an object is focused on this area, vision does not occurAlso known as the “blind spot”VisionThe Chambers of the EyeAnterior cavityAnterior chamberPosterior chamberFilled with fluid called aqueous humorPosterior cavityVitreous chamberFilled with fluid called vitreous bodyVisionThe Chambers of the EyeAqueous humorSecreted by cells at the ciliary body areaEnters the posterior chamber (posterior of the iris)Flows through the pupil areaEnters the anterior chamberFlows through the canal of SchlemmEnters into venous circulationVisionThe Chambers of the EyeVitreous bodyGelatinous material in the posterior chamberSupports the shape of the eyeSupports the position of the lensSupports the position of the retinaAqueous humor can flow across the vitreous body and over the retinaVisionAqueous HumorIf this fluid cannot drain through the canal of Schlemm, pressure builds upThis is glaucomaVitreous BodyIf this fluid is not of the right consistency, the pressure is reduced against the retinaThe retina may detach from the posterior wall (detached retina)VisionThe LensFocuses the image on the photoreceptors of the retinaConsists of concentric layers of cellsChanges shape due to:Tension in suspensory ligamentsContraction and relaxation of ciliary musclesVisionVisual PathwaysLight waves pass through the corneaPass through the anterior chamberPass through the pupilPass through the posterior chamberPass through the lensThe lens focuses the image on some part of the retinaThis creates a depolarization of the neural cellsSignal is transmitted to the brain via CN IIVisionVisual Pathways The retina (continued)The cones require light to be stimulated (that’s why we see color)At night (still has to be at least a small amount of light), the cones deactivate and the rods begin to be activated (that’s why we can see at night but we can’t determine color at night)VisionVisual Pathways Cortical IntegrationInformation arrives at the visual cortex of the occipital lobesThere is a crossover of information at the optic chiasm region ................
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