Audiology

What is sound?

A vibratory form of mechanical energy that originates from a vibrating source and travels through a medium as pressure changes.

What are compressions and rarefactions?

Alternating regions of high and low pressure that make up sound waves.

What determines the pitch of a sound?

The frequency of the sound wave.

What is frequency measured in?

Hertz (Hz).

What is the normal human hearing range?

20 Hz to 20,000 Hz.

What frequency range contains most speech sounds?

Approximately 200 Hz to 6500 Hz.

What is infrasound?

Sound below 20 Hz.

What is ultrasound?

Sound above 20,000 Hz.

What does sound amplitude relate to?

The size of pressure changes above and below atmospheric pressure.

What unit is used to measure sound amplitude?

Decibels (dB).

What is the quietest sound a healthy young ear can hear?

0 dB.

How does a 10 dB increase affect perceived loudness?

It approximately doubles perceived loudness.

What structures make up the outer ear?

The pinna and external auditory meatus (ear canal).

What is the function of the pinna?

To collect sound and funnel it down the ear canal.

What is another name for the external auditory meatus?

The ear canal.

What is the approximate length of the adult ear canal?

2.5 cm.

What protects the ear canal from dust and particles?

Cerumen (wax) and hairs.

What are the non-acoustic functions of the outer ear?

Protection of the tympanic membrane and self-cleansing.

What acoustic role does the outer ear perform?

Collects sound and boosts sound pressure at the tympanic membrane.

How much sound boost does the outer ear provide?

Approximately +5 dB.

What frequencies are most amplified by outer ear resonance?

2-5 kHz.

How much gain can outer ear resonance provide?

15-20 dB.

Why is hearing most sensitive between 2-5 kHz?

Due to resonance of the pinna and ear canal.

How does the outer ear help with sound localisation?

By modifying incoming sound frequencies depending on source direction.

What two cues are important for sound localisation?

Intensity differences and timing differences between the ears.

What structures make up the middle ear ossicles?

Malleus, incus, and stapes.

What connects the middle ear to the nasopharynx?

The Eustachian tube.

What is the function of the middle ear?

To efficiently transfer sound energy from air to cochlear fluids.

How much hearing improvement does the middle ear provide?

Up to 27 dB.

What are the three layers of the tympanic membrane?

Skin, fibrous layer, and mucosa.

What is the function of the tympanic membrane?

To vibrate in response to sound waves.

Why would hearing be poorer without the middle ear?

Most sound energy would be reflected away from cochlear fluids.

What are the two mechanisms that increase middle ear efficiency?

Surface area ratio and ossicular lever action.

How does the surface area ratio improve sound transfer?

The tympanic membrane is much larger than the stapes footplate, increasing pressure.

What is the approximate surface area ratio between the eardrum and oval window?

17:1.

How does ossicular lever action increase pressure?

The malleus is longer than the incus, increasing force at the oval window.

What is the main function of the Eustachian tube?

To equalise middle ear pressure with atmospheric pressure.

When does the Eustachian tube normally open?

During swallowing and yawning.

What is a second function of the Eustachian tube?

Drainage of middle ear fluid.

Why are middle ear infections more common in children?

Their Eustachian tubes are shorter, more horizontal, and immune systems are immature.

What is another name for the inner ear?

The labyrinth.

What are the two main functions of the inner ear?

Hearing and balance.

What fluids are found in the inner ear?

Perilymph and endolymph.

Which inner ear fluid is high in potassium?

Endolymph.

What causes hair cells to depolarise?

Movement of potassium ions from endolymph into hair cells.

What shape does the cochlea resemble?

A snail shell.

How many turns does the human cochlea have?

Approximately 2¾ turns.

What is the central core of the cochlea called?

The modiolus.

What membrane separates scala vestibuli and scala tympani?

The basilar membrane.

What joins scala vestibuli and scala tympani at the apex?

The helicotrema.

What structure sits on the basilar membrane?

The organ of Corti.

What is the function of the organ of Corti?

It contains the sensory hair cells for hearing.

What are the three scalae of the cochlea?

Scala vestibuli, scala media, and scala tympani.

What happens when the stapes pushes against the oval window?

Fluid vibrations and travelling waves are created in the cochlea.

What relieves pressure in the cochlea?

Bulging of the round window.

What is a travelling wave?

Movement of sound energy along the basilar membrane.

Where do high frequency sounds peak on the basilar membrane?

At the base.

Where do low frequency sounds peak on the basilar membrane?

At the apex.

Why is the basilar membrane frequency selective?

It is narrow and stiff at the base and wider and flexible at the apex.

What are the two types of hair cells?

Inner hair cells (IHCs) and outer hair cells (OHCs).

How many rows of inner hair cells are there?

One row.

How many rows of outer hair cells are there?

Three to four rows.

What percentage of afferent neurons connect to inner hair cells?

95%.

What is the main role of inner hair cells?

Sending auditory signals to the brain.

What is the main role of outer hair cells?

Amplifying and fine-tuning cochlear responses.

What are stereocilia?

Sensory hair bundles on hair cells.

What happens when stereocilia bend?

Ion channels open and the hair cell depolarises.

What is the role of tip links?

They pull open ion channels when stereocilia bend.

How do outer hair cells improve hearing sensitivity?

By contracting and amplifying basilar membrane movement.

What is the cocktail party effect?

The brain suppresses unwanted sounds to focus on important speech.

What are otoacoustic emissions?

Sounds produced by outer hair cell activity in the cochlea.

What are OAEs used for clinically?

Neonatal hearing screening.

What cranial nerve carries auditory information?

The eighth cranial nerve.

How is frequency information coded in the auditory nerve?

Different fibres respond best to different frequencies.

What is characteristic frequency (CF)?

The frequency to which a nerve fibre is most sensitive.

How is intensity information coded in the auditory nerve?

By firing rate, number of fibres, and fibre type.

How many fibres form the auditory nerve?

Approximately 30,000.

At what stage is the cochlea adult-like?

By birth.

Until what age do auditory pathways continue maturing?

Around six years old.

What is hearing loss?

A reduction in hearing sensitivity affecting communication and quality of life.

What percentage of the world population is affected by hearing loss?

Approximately 5%.

What are the BSA descriptors of hearing loss?

Normal, mild, moderate, severe, and profound.

What hearing level is considered normal?

Less than 20 dB HL.

What hearing level is considered mild hearing loss?

21-40 dB HL.

What hearing level is considered moderate hearing loss?

41-70 dB HL.

What hearing level is considered severe hearing loss?

71-95 dB HL.

What hearing level is considered profound hearing loss?

Greater than 95 dB HL.

What is conductive hearing loss?

A hearing loss caused by problems in the outer or middle ear.

What is sensorineural hearing loss?

A hearing loss caused by cochlear or auditory nerve dysfunction.

What is a mixed hearing loss?

A combination of conductive and sensorineural hearing loss.

What is a functional hearing loss?

An apparent hearing loss without identifiable organic pathology.

What is a typical audiogram shape in functional hearing loss?

Flat between 40-60 dB.

Why do hearing aids work well for conductive hearing loss?

Speech clarity is preserved and only amplification is needed.

What are common causes of conductive hearing loss in children?

Glue ear and middle ear infections.

What congenital conditions can cause conductive hearing loss?

Atresia, microtia, and stenosis.

Why are people with Down's syndrome prone to middle ear problems?

They have narrow Eustachian tubes and ear canals.

What is otitis externa?

Inflammation or infection of the ear canal.

What is another name for otitis externa?

Swimmer's ear.

What can impacted wax cause?

A mild conductive hearing loss.

What is tympanosclerosis?

Scarring or chalk patches on the tympanic membrane.