Study study study
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| Auditory nerve (VIII cranial nerve) |
1. cochlear branch
2. vestibular branch (superior and inferior)
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| Internal Auditory Meatus (Canal) | passageway thru temporal bone, from inner ear to base of brain
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| 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
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| Cochlear Branch of VIII nerve | Tonotopic organization
Basal fibers (high freq)- outside layer Apical fibers (low freq)- inside layer
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| 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.
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| 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.
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| auditory CNS | This network of nerve fibers is frequently referred to as the auditory central nervous system
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| Major parts of brain: | cortex (cerebrum) – (midbrain (labeled colliculi), pons, medulla)
-cerebellum –
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| cortex (cerebrum) |
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| cerebellum |
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| VIII nerve | enters brainstem at cerebellarpontine angle (CPA)
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| cerebellarpontine angle (CPA) | (cerebellum, pons, medulla meet)
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| At this level Cochlear and Vestibular branches separates: | Vestibular branch- to cerebellum (helps with balance)
-Cochlear branch- up through brainstem
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| - to cerebellum (helps with balance) -
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| ipsilateral
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| From AN, | pass through structures or nuclei (group of nerve cells with similar structures)
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| AN ends at CN | Message from the cochlea gets passed up to the cortex for
perception
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| Cochlear Nucleus (CN) | First auditory nucleus
Each CN receives input from AN on same side
Tonotopicaly organized(occurs throughout the CANS
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| 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
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| 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
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| Auditory Pathways |
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| 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
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| Superior olivary complex |
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| 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
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| Why when we stimulate one ear, both stapedius muscles contract? |
due to connections in the SOC
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| Acoustic Reflex | Some clinical uses of acoustic reflex: Detect hearing loss (difficult to test)
Absent reflexes with normal tympanogram Detect malingering
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| Acoustic reflex | Assess facial nerve function
Which branches of the facial nerve are functioning
Helps neurologist diagnose location/cause of problem
with facial nerve
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| If stapedial reflex is present | then the stapedius branch of facial nerve is working in the ear you are testing
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| SOC Reflexes | Auropalpebral reflex
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| Auropalpebral reflex |
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| Auditory Pathway | Lateral Lemniscus (LL):
InferiorColliculus(IC
Medial Geniculate Body (MGB)
Thalamus-
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| Lateral Lemniscus (LL): | nerve fiber tract-runs between SOC and IC
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| Inferior Colliculus(IC): | last brainstem nucleus
midbrainlevel– top of BS – last BS nucleus)
Last stage of decussation
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| Medial Geniculate Body (MGB): | located in thalamus
Last subcortical nucleus
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| Auditory Cortex: |
Area where sound is perceived; attach meaning to sound Located in temporal lobe
(in superior temporal gyrus, along lateral or Sylvian fissure)
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| “Heschl’s gyrus” | another name for auditory cortex
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| 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
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| DISORDERS OF AUDITORY NERVE | SNHL ipsilateral to lesion
Ability to understand speech may be greatly impaired (test
with suprathreshold speech recognition)
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| 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
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| Acoustic Neuroma | is a benign tumor, on AN
originate at 2 site
Within IAM (most) (may spread to CPA) At cerebellar-pontine-angle
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| Acoustic Neuroma | Most unilateral,except neurofibromatosis
(von Recklinghausen's disease)- bilateral
Causes numerous benign tumors on nerves throughout the
body
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| 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)
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| Acoustic Neuromas | If untreated: brainstem compression
Coma and death as it interferes with vital functions
disorder of the AN
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| DISORDERS OF CENTRAL AUDITORY NERVOUS SYSTEM | MultipleSclerosis
Presbycusis
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| Multiple sclerosis | MultipleSclerosis(MS):demyelinating disease
Myelin (sheath covering neurons that help in nerve conduction
degenerates)
Unilateral or bilateral loss
Typically mild
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| Presbycusis | CANS degeneration (including AN) as well as cochlear damage
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| 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
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| 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
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| Central Auditory Processing Disorder (CAPD) | normal pure tone average
difficulty processing auditory info (way the brain uses auditory
information)
presumed subtle damage along CANS
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| 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
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| Central Auditory Processing Disorder (CAPD | Causes(notknown-theoriesonly)
Hereditary
Subtle brain damage (e.g., difficult delivery)
Sensory deprivation (recurrent OM early yrs.)
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| Tests for disorders in CANS | monaural test
Binaural text
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| Monaural tests: | 1. filtered speech (words or sentences with LF or HF
information filtered out)
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| 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
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| 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
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| 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
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| Binaural fusion tests for Disorder of CANS |
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| 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.
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| 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.
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| 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
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| 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
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| types of testing for younger children and infants | Behavioral methods
Physiological methods
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| Behavioral methods of testing children | depend upon behavioral response from child
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| Physiological methods types of testing children | measure function without behavioral response
.g. Auditory Brainstem Response (ABR), Otoacoustic Emissions (OAEs))
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| BEHAVIORAL METHODS | Behavioral Observation Audiometry,
Conditioned Play Audiometry, and
Visual Reinforcement Audiometry (VRA)
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| Ages:Birth to 6 months.
Older, developmentally-delayed children
Simplest test: present sounds, watch for response from baby
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| 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
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| Types of responses: arousal from sleep, eyeblink, eye-widening, change in activity state, change in sucking rate, startle
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| Use Ascending approach- | BOA
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| Advantagesof BOA: | takes little time
Uses standard audiological equipment
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| Disadvantages of BOA: |
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| 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
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| conditioning technique-( Visual Reinforcement Audiometry) |
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| Visual Reinforcement Audiometry (VRA) | Conditioning phase:
Test phase:
Stimuli:
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| Test phase: | present sound alone.
If child turns, then reward with flashing toy.
Decrease intensity, find lowest level child responds
(descending approach)
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| Conditioning phase of Visual reinforcement Testing | present intense stimulus with flashing toy, child learns to associate the two.
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| Stimuli: |
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| 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
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| 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
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| Conditioned Play Audiometry | Used routinely
Ages:21 /2 o r3 to5years
What: child trained to perform play task when sound is heard
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| 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
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| Pediatric Audiometry | By 4-5 years—kids can simply raise their hand
Tympanometry
Always part of test battery
Save for last when testing children
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| Physiological Audiometry | ABR and OAEs
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| Auditory Brainstem Response testing (ABR) | Record electrical activity generated by nerve and auditory brainstem in response to sound
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| 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)
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| 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
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| Auditory Brainstem Response testing (ABR) | or newborn screening
Automated, used by technicians
Standard ABR – too time consuming to administer and
interpret
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| 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
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| 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
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| 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
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| 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
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| HA Candidacy | Communication Needs
Dexterity
Cosmetics
Financial
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| HA Candidacy | Several attempts have been made to try and determine who will benefit from HAs
prior to fitting them
Hearing thresholds
Age
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| HA Candidacy |
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| 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
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| 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
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| 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
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| 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
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| The History of Hearing Aids |
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| HA Anatomy | Microphone
• Receiver (speaker)
• Amplifier (digital processor)
• Battery
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| types of hearing aid | Custom Hearing aids
Behind-the-Ear (BTE) Hearing Aids
Receiver-in-the-canal (RIC) hearing aid
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| Hearing Aid Options | Battery Size
Volume Control
Telecoil
On/Off Switch
**Connectivity Options*
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| 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
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| 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
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| Hearing Assistance Technology (HAT) | Commonly used in schools
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| Hearing Assistance Technology (HAT) |
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