AUDITORY SYSTEMHearing is 1 of the most important sensesAn individuals quality of life is significantly affected by his ability to hear adequately

AUDITORY SYSTEMThe hearing apparatus is exquisitely sensitive to sound intensity over an enormous rangeFrequency of audible sounds is measured in decibels

AUDITORY SYSTEMProcessing of soundExternal ear (pinnae) Captures sound wavesThese waves are channeled through the external auditory meatusConveyed to the tympanic membrane

AUDITORY SYSTEMMiddle ear (tympanic cavity)Interposed between the tempanic membrane & the inner earIt is an air filled spaceSound waves are transmitted through the tempanic membrane via the ossicles MalleusHammer is attached to the tympanic membraneIncusAnvilStapesStirrup is attached to the oval window

CLINICAL CORRELATIONSOtitis media (OM)Common illnessMost commonly affects childrenRepeated incidences may result in scarring of the TMTreatmentAntibiotics secondary to concern of poststreptococcal syndromesRefractory OM is usually treated with the surgical insertion of PE tubes

CLINICAL CORRELATIONSOtosclerosisEtiologyTissue overgrowth in the area of the stapes & oval windowMay be an inherited conditionTraumaFracture of the temporal boneDirect damage to the ossiclesIndirect damageBleeding into the middle ear

CLINICAL CORRELATIONSConduction deafnessResult ofObstructed sound wavesOtits externa (swimmers ear)Accumulation of cerumenAltered sound wavesTransformation of sound wavesDamage / malformation of the pinnaeOccurs at the TM

AUDITORY SYSTEMInner earCochlea (conch shell)Contains the organ of CortiSpecialized sensory epitheliumTunnel of Corti which containsApproximately 3500 outer hair cellsApproximately 12000 inner hair cells

AUDITORY SYSTEMInner hair cell functionTransduction of sound waves into electrical signalsExtremely sensitiveInnervated by the cochlear portion of CN VIIIVestibulocochlear nerve

AUDITORY SYSTEMCochleaFunctions includeSeparating individual sound frequenciesAnalyzing individual sound frequenciesFrequencies are coded by afferent fibers situated along the cochlear spiralComplex sounds have 2 outcomesPitchPure tones that are harmonically relatedNoiseTones that are randomly related

AUDITORY SYSTEMDiagnostic tests can determine which type of deafness an individual hasDetects the differences of conduction of sound waves through air & boneRinne testTuning fork is struck & placed on the mastoid processBone + air conductionNormal is to perceive sound in the ear on that sideWhen sound is no longer perceived, the tuning fork is moved to the auditory canal where it is heard again air conduction

AUDITORY SYSTEMWeber testTuning fork is placed on the midline of the skull or foreheadNormal result is the patient perceives sound with both earsPatient with sensorineural deafness (cochlear damage)Sound is perceived in the unaffected earPatient with conduction deafnessSound is perceived in the affected ear

AUDITORY SYSTEMBrainstem auditory nucleiCochlear nucleiFunctionsAnalyze & code different sound featuresPreserve frequency informationInformation is sent to the inferior colliculusIncludesPosterior (dorsal) cochlear nucleusAnterior (ventral) cochlear nucleus

AUDITORY SYSTEMSuperior olivary complexFunctionBiurnal processing essential for accurate sound localizationMedial superior olivary nucleusPrimary nucleus in humansTrapezoid bodyMyelinated fibersPrimarily association fibers within the superior olivary complex structures / nuclei

AUDITORY SYSTEMLateral lemniscusContains axons fromSecond order neurons in the cochlear nucleiThird order neurons from the superior olivary nucleusFourth order neurons from the adjacent lateral lemniscusFunctionAuditory evoked responses to determine clinical level of brainstem function

AUDITORY SYSTEMInferior colliculusTerminal point for virtually all ascending auditory pathwaysFunctions of the paracentral nucleiTuned to frequencyReceive input from the spinal cord, posterior columns, & superior colliculusProbably involved with functions related to attention, multisensory integraton, & auditory motor reflexes

AUDITORY SYSTEM

Medial geniculate nucleusDetect both low & high frequency sound waves

AUDITORY SYSTEMPrimary auditory complexLocated in Heschels convolutionsBrodmanns area 41Brocas area for speech & languageBrodmanns areas 44 & 45Damage in this area results in Brocas aphasiaMotor aphasia speech is garbledIntact comprehension

VESTIBULAR SYSTEMFunctions includeControl of postureMovements of the body relative to the external environmentNormally this system is unapparentExceptions can occur withRough air on flightsWave motion on shipsMay result inVertigoDizzinessNausea / vomiting

VESTIBULAR SYSTEMLabyrinth consists of 2 systemsBony labyrinth is a surrounding shellFunctionsSupportProtectionMembranous labyrinthContains endolymph3 semicircular canals connected to the utricle

VESTIBULAR SYSTEMVestibular sensory receptorsHair cellsComprised of stereociliaType I hair cells form a nerve calyxType II hair cells form cylindersInnervated by single synaptic boutons

VESTIBULAR SYSTEMSemicircular canalsResponsive to rotational accelerationGenerated by turns of the head or bodyOtolith organsResponsive to linear accelerationMost prominent linear acceleration on EarthGravity

VESTIBULAR SYSTEM

Responsive to tilting of the head relative to gravityPitch Forward & backward tiltingRollSide to side tilting

VESTIBULAR SYSTEM4 Vestibular nucleiSuperior vestibular nucleusMedial vestibular nucleusLateral vestibular nucleusInferior (descending) vestibular nucleus

VESTIBULAR SYSTEMFunctions of these nuclei includeProcessing ofPositional informationMovement informationControl ofVisual reflexesPostural reflexes

VESTIBULAR SYSTEMVestibular labyrinth associated with the cerebellumOnly sensory organ in the body that doesInput terminates in the mossy fibers of the flocculonodular lobeFunctions include regulation ofEye movementsHead movementsPosture

VESTIBULAR SYSTEM

Vestibulo ocular networkFunctionAbility to keep a fixed gaze while movingExampleDriving & reading the road signs

VESTIBULAR SYSTEMVestibulo thalamo cortical networkPerceptions of motion & spatial orientation occur through this network2 areas of the thalamus are involved in these perceptionsElectrical stimulation of these areas result inMovementsDizziness

CLINICAL CORRELATIONSDizzinessDefined as non-specific spatial disorientationMay or may not involve feelings of movementMay be accompanied byNauseaPostural instability

CLINICAL CORRELATIONSVertigoSpecific perception of body movementMost commonly spinning or turning when no motion is taking placeVertigo can be elicitedSpinning around very fast & suddenly stoppingEyes exhibit nystagmusTreatmentAntivert (generic is meclizine)

CLINICAL CORRELATIONSBenign Paroxysmal Positional VertigoCommon conditionPatients experience vertigo with certain body positionsTurning over in bedGetting upBending overRising from a bent positionTreatmentHallpike maneuver

CLINICAL CORRELATIONSVestibular neuritisClinical presentation includesSevere vertigoNauseaVomitingEtiologyMost commonly an acute viral infectionHerpes simplexURIRhinorrheaInfluenza

CLINICAL CORRELATIONSTreatment of vestibular neuritis includesAntiemeticsVestibular suppressantsCorticosteriodsAntivirals

OLFACTORY SYSTEMOlfaction is defined as the sensation of odors that results from the detection of odorous substances in the environmentThese chemical stimuli must be aerosolizedOlfaction is augmented by the somatosensory system

TASTETaste (gustation) is closely related to olfactionPerception of taste relies more on the somatosensory systemCues includeThermal sensationTactile sensationChemical sensation

OLFACTORY SYSTEMDetection of odors falls into 2 main categoriesMacrosomatic animalsSense of smell is well developedFunctions includeRecognition of food substancesDetecting both predators & preyLocation of potential matesPheromones

OLFACTORY SYSTEMMicrosomatic animalsLess dependent on the sense of smellHumans are in this categoryAbility to differentiate & distinguish thousands of odorsThese odors do not have to be at high concentrations

TASTETaste is divided into 4 major categoriesSweetSaltySourBitter

TASTEThere are 2 minor categories that have been recently addedUmamiAbility to taste monosodium glutamateAllows for detection of amino acidsTaste of fatsFlavor of foods is carried in the fat content

CLINICAL CORRELATIONSDisorders of olfaction & / or tasteAffects quality of lifePatients no longer can enjoy eatingCan be a dangerous situationPatients cannot detect certain hazardsGas leakSpoiled foods

OLFACTORY SYSTEMReview of anatomyOlfactory nerve (CN I)Olfactory bulb is at the distal endNerve cilia project through the cribiform plate located in the ethmoid boneDangle down in the nasopharynxOlfactory nerve fibers project to the anterior limb of the internal capsuleNeurotransmitters in the olfactory system includeGlutamateGaba

OLFACTORY SYSTEMConnections with the cortex2 major pathwaysAssociation fibers connect the olfactory tract with other regions of the olfactory cortexExtrinsic connectionsFibers here project to the Dorsomedial nucelus of the thalamusHypothalamusHippocampus

CLINICAL CORRELATIONSDisorders of smell can be put into several categories these can be permanent or transientAnosmiaComplete loss of smellHyposmia (olfactory hypestheisa)Decreased sensitivity to odorantsAssociated with diseaseRhinitisSinusitis

CLINICAL CORRELATIONSOtherSmokingProlonged use of cocaineGeneticCertain odors cannot be detected by patients with no other diseaseReferred to as specific anosmiaHead traumaMalignanciesSeizure disordersCertain psychiatric disorders

TASTETaste receptors Located throughout the oral cavityHighest concentration TonguePalatePharynxLarynx

TASTELingual taste receptors (buds)3 major types of taste budsFungiform papillaeLocated on the anterior 2/3 of the tongueFiliform papillaeLocated on the anterior 2/3 of the tongueMore numerous than the fungiform papillaeVallate (circumvallate) papillaeLocated on the posterior 1/3 of the tongue at the junction of the oral & nasal cavities

TASTE

Single foliate papillae is located on each side of the tongueIt is configured as a series of cleftsStimulation of these papillae results in salivation

TASTETransduction of tasteClosely interconnected with olfactionRelies on enzymesLateral posterior orbitofrontal cortexReceives input from the primary taste cortexWhere appreciation of flavor, food reward, & control of feeding occurMust have integration ofTasteOlfactionVisual cues

CLINICAL CORRELATIONSDisorders of taste can also be put into categoriesAgeusiaComplete loss of tasteExtremely rareHypogeusiaDecreased taste sensitivityParageusia (dysgeusia)Distortions in the perception of taste

CLINICAL CORRELATIONSTaste alteration etiologiesMost common is drug usage / pharmacological agentsHead traumaViral infectionsBells palsyPsychiatric disordersAgingTumor