hearing science exam

Pinna

Outer ear structure containing the helix, antihelix, lobule, tragus, and concha.

Lobule

Lowest portion of the pinna (earlobe).

Helix

Outer rim of the pinna.

Antihelix

Second ridge inside the helix that divides into two crura.

Concha

Deepest bowl-shaped cavity of the pinna leading to the ear canal.

External Auditory Canal

Ear canal ~2.5 cm long, S-shaped, ending at the tympanic membrane.

Cartilaginous Portion of Ear Canal

Outer 1/3 of canal; contains hairs and cerumen glands.

Bony Portion of Ear Canal

Inner 2/3; thin skin, no glands.

Isthmus

Narrowing of the ear canal located ~4 mm before the tympanic membrane.

Functions of Outer Ear

Sound transmission, localization, and protection.

¼ Wavelength Resonator

Ear canal resonance that enhances ~2.5

Monaural Localization Cues

Elevation cues based on one ear.

Binaural Localization Cues

Azimuth cues based on both ears.

Interaural Intensity Difference (IID)

Difference in loudness between ears.

Interaural Time Difference (ITD)

Difference in arrival time/phase between ears.

Tympanic Membrane (TM)

Eardrum; cone-shaped membrane at the end of the ear canal.

Umbo

Tip of the tympanic membrane’s cone.

Pars Tensa

Tense portion of the tympanic membrane.

Pars Flaccida

Looser portion of the tympanic membrane.

Ossicles

Malleus, incus, and stapes (middle ear bones).

Manubrium of Malleus

Part of the malleus attached to the TM.

Stapes Footplate

Sits in the oval window and is held by the annular ligament.

Stapedius Muscle

Middle ear muscle attached to the stapes; part of acoustic reflex.

Tensor Tympani Muscle

Middle ear muscle attached to the malleus.

Eustachian Tube

Connects middle ear to nasopharynx; equalizes pressure.

Middle Ear Function

Converts acoustic energy to mechanical energy.

Impedance Matching

Middle ear process that boosts sound ~32 dB.

Area Ratio Transformer

TM is 17× larger than oval window, creating ~25 dB gain.

Ossicular Lever

Malleus longer than incus, adding ~1.2 dB gain.

Catenary Lever (Buckling Effect)

TM buckles, adding ~3 dB gain.

Acoustic Reflex

Stapedius contracts to protect ear from loud sounds.

Inner Ear Location

Found in the bony labyrinth of the temporal bone.

Bony Labyrinth

Cochlea, vestibule, and semicircular canals filled with perilymph.

Membranous Labyrinth

Inside bony labyrinth; filled with endolymph.

Cochlea Base

Stiff, responds to high frequencies.

Cochlea Apex

Flaccid, responds to low frequencies.

Modiolus

The central bony core of the cochlea.

Scala Vestibuli

Upper cochlear chamber filled with perilymph.

Scala Media

Middle chamber filled with endolymph.

Scala Tympani

Lower chamber filled with perilymph; ends at round window.

Helicotrema

Apex opening connecting scala vestibuli and scala tympani.

Reissner’s Membrane

Separates scala vestibuli and scala media.

Basilar Membrane

Separates scala media and scala tympani; supports Organ of Corti.

Stria Vascularis

Produces endolymph and lines lateral wall of scala media.

Tectorial Membrane

Gel membrane covering hair cells.

Organ of Corti

Hearing organ located on the basilar membrane.

Inner Hair Cells (IHCs)

1 row; release neurotransmitter to stimulate auditory nerve.

Outer Hair Cells (OHCs)

3 rows; amplify sound via electromotility.

Stereocilia

Hair-like bundles on hair cells that bend to open ion channels.

Cross-links (Tip-links)

Connect stereocilia; open and close ion channels.

OHC Electromotility

OHCs lengthen/shorten to amplify cochlear vibrations.

Vestibulocochlear Nerve (CN VIII)

Nerve carrying hearing and balance information.

Afferent Neurons

Carry information from ear to brain.

Efferent Neurons

Carry signals from brain to ear; primarily target OHCs.

Traveling Wave

Wave along the basilar membrane created by stapes motion.

Tonotopic Organization

Frequency mapping along the cochlea (base→high, apex→low).

Shearing Motion

Movement between tectorial and basilar membranes bending stereocilia.

Potassium Ion Influx

K+ enters hair cells when stereocilia bend.

IHC Function

Release neurotransmitter to trigger auditory nerve firing.

OHC Function

Amplify vibrations and improve frequency selectivity.

Place Theory

Frequencies coded by place of maximum basilar membrane displacement.

Periodicity Theory

Frequencies coded by timing/phase of neural firing.

Phase Locking

Neurons fire in sync with waveform up to ~4

Intensity Coding

Louder sounds create a broader region of basilar membrane vibration.