Hearing Science Final

What is the pinna also called?

The auricle

What is the pinna made of?

Elastic cartilage covered by skin

What is the helix of the pinna?

The outer rim of the ear

What is the concha of the pinna?

The bowl-shaped depression that funnels sound into the ear canal

What is the lobule of the pinna?

The earlobe

What is the tragus?

A small cartilaginous projection in front of the ear canal opening

How long is the external ear canal?

Approximately 2.5 cm

What makes up the outer third of the ear canal?

Cartilage

What makes up the inner two-thirds of the ear canal?

Bone

What does the outer portion of the ear canal contain?

Cerumen (earwax) glands and hair follicles

What is the primary sound-collecting function of the pinna?

It funnels sound waves toward the ear canal and tympanic membrane

Which part of the pinna is most important for funneling sound?

The concha

What frequency range does the outer ear amplify?

1–5 kHz

What is the resonant frequency of the external ear canal?

~2.5 kHz

How much gain does the outer ear provide near resonance?

Up to 10–15 dB

Why is the 1–5 kHz amplification range evolutionarily significant?

It overlaps with frequencies critical for speech perception (especially consonants)

What are Head-Related Transfer Functions (HRTFs)?

Direction-specific spectral cues created by pinna reflections used to localize sound

In which planes are HRTFs most important for localization?

The vertical plane (up vs. down) and median plane (front vs. back)

What cue helps localize sounds in the horizontal plane — timing?

Interaural time difference (ITD)

What cue helps localize sounds in the horizontal plane — intensity?

Interaural level difference (ILD)

How does the ear canal protect the tympanic membrane?

Its tube shape blocks foreign objects

cerumen and hairs trap dust and debris

What is the tympanic membrane also called?

The eardrum

What shape is the tympanic membrane?

Thin and cone-shaped

What does the tympanic membrane separate?

The outer ear from the middle ear

What are the three auditory ossicles?

Malleus

What are the common names of the three ossicles?

Hammer (malleus)

What distinction do the ossicles hold in the human body?

They are the smallest bones in the human body

Where does the ossicular chain begin and end?

From the tympanic membrane to the oval window of the cochlea

What are the two middle ear muscles?

Tensor tympani and stapedius

Which muscle is attached to the malleus?

Tensor tympani

Which muscle is attached to the stapes?

Stapedius

What distinction do the middle ear muscles hold?

They are the smallest skeletal muscles in the human body

What is the Eustachian tube's function?

Equalizes air pressure between the middle ear and the nasopharynx

When does the Eustachian tube open?

During swallowing or yawning

What is acoustic impedance mismatch?

The problem of transferring sound from low-impedance air to high-impedance cochlear fluid

How much sound energy is lost without the middle ear due to impedance mismatch?

~99.9% reflected — a 30 dB loss

What is the area ratio mechanism of the middle ear?

The TM (~55 mm²) concentrates force onto the small stapes footplate (~3.2 mm²)

What gain does the ossicular lever system provide?

~2 dB

What is the lever ratio of the malleus to incus?

Approximately 1.3:1

What is the buckling mechanism of the tympanic membrane?

The TM's conical shape causes the umbo to move more than the edges

What is the acoustic reflex also called?

The stapedius reflex

At what sound level does the acoustic reflex trigger?

Typically >85 dB SPL

What happens during the acoustic reflex?

Stapedius and tensor tympani contract

Is the acoustic reflex unilateral or bilateral?

Bilateral — loud sound in one ear triggers the reflex in both ears

What is the main limitation of the acoustic reflex?

Its latency of ~25–150 ms means it cannot protect against sudden impulse sounds like gunshots

Which frequency range does the acoustic reflex primarily reduce?

Low frequencies

What does the tensor tympani primarily respond to?

Non-acoustic stimuli (e.g.

What is the cochlea shaped like?

A snail shell

How long is the uncoiled cochlea?

~35 mm

How many turns does the cochlea make?

~2.5 turns around the modiolus

What is the modiolus?

The bony central axis of the cochlea

What are the three scalae of the cochlea?

Scala vestibuli

What fluid fills the scala vestibuli?

Perilymph

What fluid fills the scala media?

Endolymph

What fluid fills the scala tympani?

Perilymph

What makes endolymph unique compared to other extracellular fluids?

It has high K+ and low Na+ concentration

What maintains the ionic composition of endolymph?

The stria vascularis

What is the endocochlear potential and its value?

A +80 mV electrical potential in the scala media that drives hair cell transduction

What is the oval window connected to?

The scala vestibuli

it is where the stapes footplate presses

What is the round window's function?

Acts as a pressure relief valve for the scala tympani

What membrane separates the scala vestibuli from the scala media?

Reissner's membrane

What membrane separates the scala media from the scala tympani?

The basilar membrane

How does the basilar membrane vary from base to apex — width?

Narrow at the base

How does the basilar membrane vary from base to apex — stiffness?

Stiff at the base

What frequencies does the base of the basilar membrane respond to?

High frequencies

What frequencies does the apex of the basilar membrane respond to?

Low frequencies

What is the helicotrema?

A small opening at the cochlear apex connecting scala vestibuli and scala tympani

allows pressure equalization for very low frequencies

What is the Organ of Corti?

The sensory epithelium on the basilar membrane that converts mechanical vibration into electrical signals

How many rows of inner hair cells are there?

1 row (~3

How many rows of outer hair cells are there?

3 rows (~12

What is the primary function of inner hair cells?

Sensory transduction — release glutamate onto auditory nerve fibers when deflected

What neurotransmitter do IHCs release?

Glutamate

How many Type I auditory nerve fibers connect to each IHC?

~20 fibers per IHC (many fibers to one IHC)

What is the primary function of outer hair cells?

Mechanical amplification — electromotility amplifies basilar membrane vibration

What is electromotility?

The ability of OHCs to change their length in response to electrical signals

What is the innervation pattern of Type II fibers onto OHCs?

One Type II fiber innervates ~10 OHCs (one-to-many)

What is the most common cause of sensorineural hearing loss?

Damage to outer hair cells (OHCs)

What are stereocilia?

Mechanosensitive hair-like projections on top of hair cells

What connects stereocilia and gates the ion channels?

Tip links

What ion rushes in when stereocilia are deflected?

Potassium (K+) from the endolymph

What triggers neurotransmitter release at the base of an IHC?

Depolarization from K+ influx leads to Ca2+ influx

What is a traveling wave?

A wave that propagates from the cochlear base toward the apex when the stapes pushes on the oval window

What is the characteristic frequency (CF) of a basilar membrane location?

The frequency at which that location produces its maximum displacement

What is tonotopic organization?

The spatial mapping of sound frequency along the basilar membrane — preserved all the way to auditory cortex

Where on the BM does 20

000 Hz produce maximum displacement?

Where on the BM does 200 Hz produce maximum displacement?

Near the apex

What is a tuning curve?

A V-shaped plot of the minimum SPL needed at each frequency to activate a single auditory neuron

the sharp tip is at the CF

What does the sharp tip of a tuning curve demonstrate?

Fine frequency selectivity — the neuron needs the least energy at its CF

What is compressive non-linearity of the BM?

At CF

What happens to BM response away from the CF?

It becomes more linear (less compression)

Why is BM compression important?

It allows the auditory system to handle ~120 dB of dynamic range while remaining sensitive to soft sounds

What cranial nerve carries auditory information?

Cranial nerve VIII (vestibulocochlear nerve)

How many fibers does the human auditory nerve contain?

~30

Where do spiral ganglion neurons sit?

In the modiolus

What percentage of auditory nerve fibers are Type I?

~90–95%

Are Type I fibers myelinated or unmyelinated?

Myelinated