SHS 450 Midterm 1

Audiology

study of hearing mechanisms, assessment of hearing, hearing and listening disorders, rehabilitation of individuals with hearing loss

Audiology as it relates to SLP

preform hearing screenings, refer children who do not pass, collaborate with audiologists on follow-up and outcomes, counsel and educate families, service providers, and educators about hearing loss

Roles of an audiologist

identify, assess, manage, and treat hearing and balance disorders, select and fit amplification, counsel and train in communication skills, research, teach and supervise

Incidence

number of new cases per year

Prevalence

number of cases in the population

Incidence vs prevalence of hearing disorders

360 million (5.3%) persons in the world have a debilitating hearing loss

48 million (14.7%) Americans report some degree of hearing loss

2-3 of every 1000 children (0.3%) in America are born with hearing loss in one or both ears

Licensure vs certification

license: legally required by each state to practice audiology

certification: voluntary credential

Certifying bodies in audiology

American Board of Audiology (ABA)

American Speech-Language Hearing Association (ASHA)

3 divisions of peripheral auditory system

outer ear, middle ear, inner ear

Outer ear structures

pinna and ear canal

Middle ear structures

tympanic membrane and ossicular chair (malleus, incus, stapes)

Inner ear stuctures

cochlea and balance organs

Outer ear (amplification)

pinna funnels sounds into the ear canal

pinna provides cues for localizing sound

ear canal resonance amplifies sounds from 2000-3000 Hz

Middle ear (amplification)

middle ear amplifies incoming sound waves

area effect: tympanic membrane larger than oval window

lever effect: malleus is longer than incus

stapes rocks back and forth into the oval window, setting cochlear fluids into motion

Inner ear (amplification)

fluid movement causes movement of the basilar membrane

travels as wave from base to apex

traveling wave reaches maximum displacement then dissipates

• high frequencies: base

• low frequencies: apex

tonopopic organization due to changes in stiffness and width

• stiffer in base, less stiff in apex

• narrower in base, wider in apex

Inner ear transmission of sound

hair cells rest on basilar membrane

basilar membrane movement causes shearing of hair cells

outer hair cells amplify basilar membrane motion

inner hair cells stimulate the auditory nerve

hair cell is negatively charged at rest, shearing of hair cells allows K+ and Ca2+ to enter the hair cells

positive ions entering hair cells causes depolarization

depolarizing inner hair cells releases neurotransmitters that stimulate the auditory nerve

Outer hair cells and the cochlear amplifier

outer hair cells change their shape as ions flow in and out

change in shape amplifies basilar membrane motion

healthy outer hair cells improve sensitivity to low-level sounds

outer hair cells sensitive to aging, toxins, and noise

conductive mechanism

outer ear and middle ear

Sensorineural mechansim

inner ear (sensory) and auditory nerve (neural)

Air conduction

vibrations traveling through air and transmitted to outer ear, middle, then inner ear

Bone conduction

vibrations are sent directly through bone to stimulate the inner, bypasses conductive mechanism, own voice is heard partially through bone conduction

Three types of hearing loss

conductive, sensorineural, mixed

Conductive hearing loss

pathology in outer and/or middle ear

air-conducted sound is negatively affected by outer/middle ear

bone-conducted sound is transmitted efficiently

Example of conductive hearing loss

cerumen impaction, tympanic membrane, perforation, atresia microtia

Example of sensorineural hearing loss

noise-induced hearing loss, acoustic neuroma

Sensorineural hearing loss

pathology in inner ear and/or nerve

air and bone-conducted sound are negatively affected by inner ear/nerve

Mixed hearing loss

pathology in outer/middle ear and inner ear/nerve

air conducted sound is negatively affected by outer/middle ear and inner ear/nerve

bone-conducted sound is negatively affected by inner ear/nerve

Tuning fork

a two-pronged, fork-like instrument that vibrates when struck; used to test hearing, especially bone conduction

Where to place a tuning fork

air conduction: tines parallel to pinna

bone conduction: stem on mastoid or stem on midline

Stenger Principle

patient perceives sound in the ear that receives the loudest intensity

Weber test

detects unilateral hearing loss

Weber test: placement

place tuning fork on midline

ask patient where they hear the sound (right, left, both)

Weber test: midline outcome

suggests no unilateral hearing loss

sound is reaching each cochlea at equal intensity

patients with bilateral hearing loss may also hear sound in midline

Weber test: lateralizing outcome

suggests a unilateral conductive hearing loss in that ear

conductive hearing loss increases the intensity of bone-conducted sound in that ear