hearing science exam

peripheral auditory system

• captures sound signals, transmits and
  transforms them into information that can be
  experienced as an auditory percept

• outer, middle, inner ear

central auditory system

• interprets auditory information delivered by the peripheral auditory system

• cochlear nerve, brain stem, thalamus, auditory cortex

transducer

a device that converts energy from one form to another

conductive mechanism

• natural transmission (movement) of sound through the outer ear, ear drum, and middle ear

• outer and middle ear

sensorineural mechanism

• transmission of energy through the
  cochlea (sensory organ) and the auditory nerve (neural structure)

• cochlea and auditory nerve

outer ear conductive mechanism

• collects sound waves and amplifies them during transfer to the ear drum

• transfer of acoustic energy

• pinna and ear canal

pinna

• helps with sound localization

• channel sound waves into the ear canal

ear canal

• protective function: cartilaginous part lined with hair follicles and glands that secrete cerumen (lubricates the canal, hindersinsect entry)

• resonator: open at the pinna and closed at the eardrum; the resonant frequency of the ear canal is ~3000-3500 Hz

• high frequency resonance amplifies high-frequency sounds(e.g., fricatives) by 10-15 dB

ear drum

• semitransparent oval membrane between the outer ear and the middle ear

• transforms pressure changes of sound waves into mechanical vibrations

middle ear conductive mechanism

• increases the amplitude of sound
  waves to overcome the impedance mismatch between the middle ear (air) and the inner ear (fluid)

• transfer of mechanical energy

• malleus, incus, stapes, eustachian tubes

impedance

resistance to movement; a measure of the difficulty of signal transmission through a medium

impedance mismatch

air-filled middle ear offers low impedance
to sound waves; fluid-filled inner ear offers high impedance to sound wave

pressure amplification

• relies on the difference in the surface area of the tympanic membrane (85 mm2) to the oval window (3 mm2)

• decrease in area (oval window vs. tympanic membrane) results
  in increased pressure

Eustachian tube

• middle ear ventilation and drainage

• middle ear end open; nasopharyngeal opening typically closed except during swallowing and yawning

ventilation

equalize air pressure between the otherwise closed middle ear and the external atmosphere because atmospheric air enters the middle ear when the pharyngeal end open

drainage

drain middle ear mucus to the pharynx where it is swallowed

middle ear infection

no mucus drainage due to blockage of
pharyngeal opening

inner ear sensorineural mechanism

• balance and hearing

• transfer of hydraulic and electrical energy

• vestibular system and cochlea

vestibular system

• organ of balance

• monitors the motion and position of the head in space

• filled with fluid (endolymph)

• point of origin of the vestibular nerve

basilar membrane

• base of the cochlear duct (scala media)

• narrow and stiff at the base; wide and flexible at the apex

• organ of corti runs along the length
  

tonotopic arrangement

high frequency sounds processed at the base; low-frequency sounds processed at the apex

organ of corti

• sensory organ of hearing, which transforms fluid vibrations into electrical energy

• contains the sensory cells for hearing (inner and outer hair cells), whose tips are embedded within the tectorial membrane

outer hair cells

movement amplifies the signal

inner hair cells

release neurotransmitters to excite the auditory nerve