Hearing and Balance

This flashcard set consists of extensive neuroscience definitions and examples of the auditory and vestibular system. These are taken from Behavioral Neuroscience (Breedlove & Watson, 2023) and made as a study guide for Exam 3 in Behavioral Neurobiology at BYU-I.

Two parts of the external ear

Pinna and ear canal

Pinnae (sing. pinna)`

The fleshy objects protruding out both sides of the head that we call “ears”

Ear canal

The tube that propagates sound from the pinna to the middle ear

Parts of the middle ear

Tympanic membrane and ossicles

Tympanic membrane

The taut membrane separating the external ear canal from the middle ear (the eardrum)

Ossicles

The tiny bones that connect the tympanic membrane to the inner ear, using muscle connections to protect it from loud noises

The three ossicles are

malleus, incus, and stapes

Tensor tympani

A muscle in the middle ear connected to the malleus to protect the inner ear from loud noises

Stapedius

A middle ear muscle connected to the stapes to protect the inner ear from loud noises

Oval window

A special location on the cochlea’s surface that receives vibrations from the ossicles

Two parts of the inner ear

The cochlea and vestibular apparatus

Cochlea

A fluid-filled structure coiled in the temporal bone of the skull, the auditory portion of the inner ear

Three parallel canals of the cochlea

Scala vestibuli, scala media, scala tympani

Round window

A membrane opening of the inner ear separating the scala tympani from the middle ear

Organ of Corti

The receptor system in the scala media that converts sound vibration into neural activity

Hair cells

Auditory sensory cells imbedded in the basilar membrane of the organ of Corti (in the cochlea)

Inner hair cells (IHCs)

A subset of hair cells numbering 3,500 in a single row near the central axis of the cochlea

Outer hair cells (OHCs)

A subset of auditory hair cell receptors in three rows numbering about 12,000

Stereocilia

A relatively stiff hair protruding from hair cells in the auditory or vestibular system

Tip links

Fine, rodlike fibers that run across the tops of stereocilia in the cochlea’s middle canal

Tectorial membrane

A membrane atop the organ of Corti in the cochlear duct, whose indentations attach to stereocilia of hair cells

Sound vibration journey into neural activity

Sound vibrations vibrate the tympanic membrane, which sends waves to the oval window through the ossicles, causing fluid to wave in the scala vestibuli, thereby making the basilar membrane ripple; mechanical vibrations of the membrane bend stereocilia, whose ends are bound by tip links to increase tension and open mechanically-gated (K+ and Ca++) ion channels

Place coding theory

A principle of frequency that suggests the basilar membrane is tapered to allow sensitivity to different frequencies, with experiences of high pitch peaking near the base and low pitch peaking near the apex

Treble

Experiences of high pitch

Bass

Experiences of low pitch

Temporal coding

A theory suggesting that auditory neurons fire at a rate proportional to the sound cycle (hertz)

Amplitude

The changes in air pressure measured by dyne/cm2

Amplitude is perceived as __________, measured by _____

Loudness, decibels (dB)

Frequency

The number of cycles per second, measured in hertz (Hz)

Frequency is perceived as _______.

Pitch

Path of sound vibrations (as neural signals)

Cochlea - CN VIII - Dorsal/Ventral cochlear nuclei - superior olivary nuclei - inferior colliculi - medial geniculate nuclei - primary auditory cortex (A1)

Interaural intensity differences (IIDs)

Perceived differences in loudness between the two ears that help localize sound sources

Interaural temporal differences (ITDs)

Differences between ears in arrival of sounds

Onset disparity

The difference between the two ears in hearing the beginning of the sound

Ongoing phase disparity

The continuing mismatch between two ears in the time of arrival of each peak and trough of a sound wave

Duplex theory (of sound)

Suggests that we localize sound by combining information about intensity (IIDs) and latency differences (ITDs) between the two ears

Spectral filtering

Alteration of the amplitude of specific frequencies in a sound through the shape and angles of the pinnae, helping to localize elevation of vertical sounds

Two ways in which frequency properties of a sound are coded

According to the 1) distribution of excitation among cells (place-coding or tonotopic organization), and 2) the temporal pattern of discharge in cells projecting to A1

Minimal discriminable frequency difference

The ability to detect changes in frequency (pitch), with detectable differences at 2 Hz for sounds at 2000Hz

Infrasounds

Sounds at frequencies lower than 10Hz

Ultrasound

Sounds at frequencies over 20,000Hz

Azimuth

Sound localization on the horizontal plane

Heschl’s gyrus (temporal transverse gyrus)

Part of A1 where music is first processed, being twice as large among brains of musicians

Amusia

The inability to discern tunes accurately

Hearing loss

Decreased sensitivity to sound, ranging from moderate to severe

Deafness

Loss of hearing so profound that speech can’t be perceived even with hearing aids

Conduction deafness

Occurs when auditory stimuli are prevented from reaching the cochlea, such as the fusion of ossicles

Sensorineural deafness

When damage to the cochlea or auditory nerve results in an inability to transduce sound ripples into action potentials, such as from loud noise exposure, metabolic problems, infections, etc.

Ototoxic

Toxic to the ears (especially middle/inner)

Central deafness

Impairment in hearing from damage to auditory brain regions, like from strokes, tumors, or other traumatic injuries

Word deafness

The specific ability to hear words while other sounds can be detected

Cortical deafness

A rare impairment marked by difficulty recognizing almost all complex sounds (verbal or nonverbal), caused by bilateral lesions of auditory cortex

Streptomycin, gentamicin

Antibiotics with ototoxic qualities

Semicircular canals

Three fluid-filled tubes of the vestibular system that detect angular acceleration of pitch (nodding), yaw (shaking head), and roll (tilting head)

Utricle

Small, fluid-filled sac in the vestibular system above the saccule that responds to static positions of the head

Saccule

Small, fluid-filled sac in the vestibular system under the utricle that responds to static positions of the head

Ampulla (pl. ampullae)

The enlarged regions of semicircular canals of the vestibular system that contain the receptor hair cells

Cupula

The hair cell-containing gelatinous structure in the semicircular canals of the vestibular system

Otoliths

Small crystals (“ear stones”) on the otolithic membrane

Otolithic membrane

A gelatinous sheet in the utricles/saccules that lags when the head moves, bending the stereocilia of nearby hair cells to track linear acceleration/deceleration

Lateral-line system

A sensory system (possible precursor to mammalian vestibular and auditory systems) found in some fishes and amphibians that detects water motion in relation to body surface

Vestibular nuclei

Brainstem nuclei that receive vestibular information through CN VIII

Pathway of vestibular information

Vestibular apparatus, CN VIII, vestibular nuclei (or straight to cerebellum), eye motor nuclei / thalamus / cerebral cortex

Pathway of auditory system

CN VIII, superior olivary nuclei, inferior colliculi, medial geniculate nucleus, primary auditory cortex (A1)

Vestibulo-ocular reflex (VOR)

The brainstem mechanism that maintains gaze on a visual object during head movements, continues when eyes are closed

Motion sickness

Nausea produce from unnatural passive movement, especially uncontrolled movements

Somatogravic illusion

When linear acceleration is misinterpreted as a climb (upward tilt), requiring pilots to take further training and rely on instruments