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Audiology Final Exam

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Auditory nerve (VIII cranial nerve) 1. cochlear branch 2. vestibular branch (superior and inferior)
Internal Auditory Meatus (Canal) passageway thru temporal bone, from inner ear to base of brain
Internal Auditory Meatus (Canal) contains: 1. cochlear branch of VIII nerve 2. vestibular branch of VIII nerve 3. VII nerve- Facial nerve 4. internal aud. artery-blood supply to cochlea
Cochlear Branch of VIII nerve Tonotopic organization Basal fibers (high freq)- outside layer Apical fibers (low freq)- inside layer
Auditory Nerve The electrical potentials generated by auditory nerve fibers are called all-or-none action potentials because they do not vary in amplitude when activated.
Auditory Central Nervous System Once the action potentials have been generated in the cochlear branch of the auditory nerve, the electrical activity progresses up toward the cortex.
auditory CNS This network of nerve fibers is frequently referred to as the auditory central nervous system
Major parts of brain: cortex (cerebrum) – (midbrain (labeled colliculi), pons, medulla) -cerebellum –
cortex (cerebrum)
VIII nerve enters brainstem at cerebellarpontine angle (CPA)
cerebellarpontine angle (CPA) (cerebellum, pons, medulla meet)
At this level Cochlear and Vestibular branches separates: Vestibular branch- to cerebellum (helps with balance) -Cochlear branch- up through brainstem
- to cerebellum (helps with balance) -
From AN, pass through structures or nuclei (group of nerve cells with similar structures)
AN ends at CN Message from the cochlea gets passed up to the cortex for perception
Cochlear Nucleus (CN) First auditory nucleus  Each CN receives input from AN on same side  Tonotopicaly organized(occurs throughout the CANS
Cochlea Nucleus (CN)  Many nerve fibers in brain decussate(crossover)  In CANS, first decussation (cross-over) occurs after CN  Some fibers go across the brain to the other side
Auditory Pathways  Ipsilateral pathway (uncrossed)  Contralateral pathway (crossed)-  Strongest paths- 80% of fibers cross over eventually and reach opposite cortex  True for much of the brain
Auditory Pathways
Superior Olivary Complex (SOC)  Compares time and intensity between ears  Remember how the Pinna helps to localize?  involved in locating height and front vs. back
Superior olivary complex
Superior Olivary Complex (SOC)  SOC involved in some reflexes  automatic response to sensory stimulus  Stapedial(Acoustic)reflex:  cochlea-VIII N-CN-SOC-motor nucleus of VII N-Stapedius branch of VII N-Stapedius muscle
 Why when we stimulate one ear, both stapedius muscles contract?   due to connections in the SOC
Acoustic Reflex  Some clinical uses of acoustic reflex:  Detect hearing loss (difficult to test) Absent reflexes with normal tympanogram Detect malingering
Acoustic reflex  Assess facial nerve function Which branches of the facial nerve are functioning Helps neurologist diagnose location/cause of problem with facial nerve
If stapedial reflex is present then the stapedius branch of facial nerve is working in the ear you are testing
SOC Reflexes Auropalpebral reflex
Auropalpebral reflex
Auditory Pathway  Lateral Lemniscus (LL):  InferiorColliculus(IC  Medial Geniculate Body (MGB)  Thalamus-
Lateral Lemniscus (LL): nerve fiber tract-runs between SOC and IC
Inferior Colliculus(IC): last brainstem nucleus midbrainlevel– top of BS – last BS nucleus)  Last stage of decussation
Medial Geniculate Body (MGB): located in thalamus  Last subcortical nucleus
Auditory Cortex: Area where sound is perceived; attach meaning to sound Located in temporal lobe (in superior temporal gyrus, along lateral or Sylvian fissure)
“Heschl’s gyrus” another name for auditory cortex
Tonotopic organization is maintained all the way through the cortex  Lower frequencies are on the surface, higher frequencies are located deeper  Pitch perception – which neurons in AC fire
DISORDERS OF AUDITORY NERVE SNHL ipsilateral to lesion  Ability to understand speech may be greatly impaired (test with suprathreshold speech recognition)
2 types SNHL disorders of the auditory nerve: What are they? cochlear  Retrocochlear–AN beyond cochlea-  usually affects ability to understand speech more than cochlear
Acoustic Neuroma is a benign tumor, on AN originate at 2 site  Within IAM (most) (may spread to CPA)  At cerebellar-pontine-angle
Acoustic Neuroma Most unilateral,except neurofibromatosis  (von Recklinghausen's disease)- bilateral  Causes numerous benign tumors on nerves throughout the body
Acoustic Neuroma Tumors Unilateral SNHL (begins in high freqs, progresses) Difficulty understanding speech (more than expected based on degree of PT loss Tinnitus  Dizziness (pressure on vestibular branch of AN)  Facial paralysis (pressure on VII nerve)
Acoustic Neuromas If untreated: brainstem compression  Coma and death as it interferes with vital functions disorder of the AN
Multiple sclerosis MultipleSclerosis(MS):demyelinating disease  Myelin (sheath covering neurons that help in nerve conduction degenerates)  Unilateral or bilateral loss  Typically mild
 Presbycusis  CANS degeneration (including AN) as well as cochlear damage
 Many different paths from CN to cortex;  Lesion may eliminate 1 path, but other routes carry enough info for simple tasks  Why: nerve fiber branching to form many contralateral fibers, more redundancy  Many different paths from CN to cortex;  Lesion may eliminate 1 path, but other routes carry enough info for simple tasks
DISORDERS OF CENTRAL AUDITORY NERVOUS SYSTEM ( testing improvement ) To detect pathology in CANS, need to make task more difficult!!  Stress the auditory system  Tasks that require all circuits to work  Use “degraded” speech tests  E.g. add noise, distortion, competing message
Central Auditory Processing Disorder (CAPD) normal pure tone average difficulty processing auditory info (way the brain uses auditory information) presumed subtle damage along CANS
Central Auditory Processing Disorder (CAPD) possibles symptons Possiblesymptoms:  Difficulty listening in background noise  Difficulty understanding rapid or distorted speech  Difficulty following spoken directions  Inconsistent auditory attention
Central Auditory Processing Disorder (CAPD Causes(notknown-theoriesonly)  Hereditary  Subtle brain damage (e.g., difficult delivery)  Sensory deprivation (recurrent OM early yrs.)
Tests for disorders in CANS monaural test Binaural text
Monaural tests:  1. filtered speech (words or sentences with LF or HF information filtered out)
speech with interference type of monaural test (test for disorder in the CAN Masking noise or competing message- both to same ear  Patients asked to ignore noise and repeat message  Typical problem for CANS disorders
Tests for disorders in CANS ( Binaural tests) Dichotic speech tests (diff signal to each ear) Binaural fusion: sensitive to brainstem dysfunctions Low frequency information to one ear high frequency to the other
Dichotic speech tests (diff signal to each ear)  Words, sentences, or digits  Repeat items in both ears/ignore input to one ear and repeat signal in the other ear
Binaural fusion tests for Disorder of CANS
Clinical Auditory Electrophysiology Clinical auditory electrophysiology involves recording the gross electrical potentials representing the activity of hundreds or thousands of individual hair cells or nerve fibers.
Clinical Auditory Electrophysiology ( Auditory brainstem response) The electrical potentials are usually recorded from remote locations on the surface of the head and require amplification and computer averaging of at least several hundred stimulus presentations to be visible.
The auditory brainstem response (ABR) – Very robust and can be recorded reliably and easily – Sensitive to dysfunction occurring from the auditory periphery to the upper brainstem of the auditory CNS
The auditory brainstem response (ABR) Useful in assisting with detection of neurologic problems along a large portion of the auditory CNS – Can be used to estimate hearing loss
types of testing for younger children and infants Behavioral methods Physiological methods
 Behavioral methods of testing children depend upon behavioral response from child
Physiological methods types of testing children measure function without behavioral response .g. Auditory Brainstem Response (ABR), Otoacoustic Emissions (OAEs))
BEHAVIORAL METHODS  Behavioral Observation Audiometry, Conditioned Play Audiometry, and Visual Reinforcement Audiometry (VRA)
 Ages:Birth to 6 months. Older, developmentally-delayed children  Simplest test: present sounds, watch for response from baby
 Sound booth necessary  Subject state: newborns: light sleep  Older infants: light sleep or held quietly  Two testers best  Test in sound field (sounds through speakers)  Stimuli: speech first  Then warble tones or NBN-various freqs
 Types of responses: arousal from sleep, eyeblink, eye-widening, change in activity state, change in sucking rate, startle
Use Ascending approach- BOA
Advantagesof BOA: takes little time  Uses standard audiological equipment
Disadvantages of BOA:
Visual Reinforcement Audiometry (VRA)  Also called Conditioned Orientation Reflex (COR)  Used routinely  Ages= age 6 months to about 2.5 to 3 years  Note: not all 6 month babies can do, but should be able to do by about 9 months
conditioning technique-( Visual Reinforcement Audiometry)
Visual Reinforcement Audiometry (VRA)  Conditioning phase: Test phase: Stimuli:
Test phase: present sound alone.  If child turns, then reward with flashing toy.  Decrease intensity, find lowest level child responds (descending approach)
 Conditioning phase of Visual reinforcement Testing present intense stimulus with flashing toy, child learns to associate the two.
Advantages of VRA:  Can assess across freq. range with good reliability  Can assess degree of loss (will resp. down to threshold)  Not reflexive  Takes little time
Disadvantages of VRA: If speakers used, does not assess ears individually  If developmentally delayed (below 6-9 mo level)-will not condition  Visually impaired-cannot test  Older kids (2-3 yrs)- may get bored rapidly
Conditioned Play Audiometry Used routinely  Ages:21 /2 o r3 to5years  What: child trained to perform play task when sound is heard
Conditioned Play Audiometry Usually done face to face with portable audiometer- under headphones  Can also do in sound field (with assistant)  Condition with loud stimuli  Then descend to threshold
Pediatric Audiometry  By 4-5 years—kids can simply raise their hand  Tympanometry  Always part of test battery  Save for last when testing children
Physiological Audiometry ABR and OAEs
Auditory Brainstem Response testing (ABR) Record electrical activity generated by nerve and auditory brainstem in response to sound
Auditory Brainstem Response testing (ABR) how it is recorded Electrodes taped to scalp  Stimulus through earphone  Electrodes connected to computer  Electrodes pick up neural discharges in resp. to stim  Patient state- still and relaxed (sleeping)
Auditory Brainstem Response testing (ABR) Find lowest level that ABR can be elicited-  Correlates closely with hearing threshold  Test procedures can take 1-2 hours  Actual test time - ~30 minutes  Longer than BOA, VRA  More expensive  Needs specialized equipment
Auditory Brainstem Response testing (ABR) or newborn screening  Automated, used by technicians  Standard ABR – too time consuming to administer and interpret
Auditory Brainstem Response testing (ABR) How works:  Apply electrodes, place earphone, start test  Machine presents low level stimulus, analyzes response for presence of ABR  Result is pass or fail  Don’t get degree of loss- need follow-up
Otoacoustic Emissions (OAEs) If OHC’s damaged and hearing loss is 25-30 dB or more: OAEs will be absent  Therefore, good hearing screening tool takes only few minutes,no cooperation required  Useful for newborn hearing screening
Hearing Loss Facts and Figures  One in 5 people who would benefit from a hearing aid actually use one  On average, people with hearing loss ~5 years before they do something about it  More and more young people experience hearing loss
Hearing Loss Facts and Figures One in 5 people who would benefit from a hearing aid actually use one  On average, people with hearing loss ~5 years before they do something about it  More and more young people experience hearing loss
HA Candidacy  Communication Needs  Dexterity  Cosmetics  Financial
HA Candidacy Several attempts have been made to try and determine who will benefit from HAs prior to fitting them  Hearing thresholds  Age 
HA Candidacy
Patient Based Factors Influencing HA User Success Acceptance of hearing loss • Motivation to wear HA • Awareness of hearing needs ▫ Degree of disability (difficulty hearing) Effort put forth to listen ▫ Degree of hearing handicap
Patient Based Factors Influencing HA User Success Degree of hearing handicap (Impact on life style) • “Listening” attitude • Appropriate expectations • Social impact of HI • Cost • Age
Once you have decided to purchase a hearing aid… ***Style, technology, unilateral vs. bilateral***  For a symmetrical hearing loss, we will always recommend two hearing aids  Impressions are taken for custom fit HAs or earmolds
Once you have decided to purchase a hearing aid… ~2 weeks later, patients return for the fitting of the HA  At the HA fitting, patients are taught how to care for the hearing aid, and the initial settings are programmed into the HA  By law, patients have a 45-day trial period when purchasing a HA
The History of Hearing Aids
HA Anatomy Microphone • Receiver (speaker) • Amplifier (digital processor) • Battery
types of hearing aid Custom Hearing aids Behind-the-Ear (BTE) Hearing Aids Receiver-in-the-canal (RIC) hearing aid
Hearing Aid Options Battery Size  Volume Control  Telecoil  On/Off Switch  **Connectivity Options*
Hearing Aid Batteries ▫ Power source for the HA ▫ Range in size depending on the power of the aid • Larger battery= more power • Small battery= less power ▫ Battery life ranges from 3 days to several weeks
Hearing Aid Batteries Sizes are color coded ▫ Zinc Air-not active until tab is pulled off • Once tab has been removed reaction cannot be stopped
Hearing Assistance Technology (HAT) Commonly used in schools
Hearing Assistance Technology (HAT)