Ch 9 - Hearing

amplitude (or intensity)

in reference to sound, the magnitude of displacement of a pressure wave

perceived as loudness

frequency

the number of times per second that a pattern of pressure change repeats

perceived as pitch

hertz (Hz)

a unit of measure for frequency

1 of these equals 1 cycle per second

decibel (dB)

a unit of measure for the physical intensity of sound

defines the difference between two sounds as the ration between two sound pressures

pure tone or sine tone

the single waveform for which variation as a function of time is a sine function

spectrum

a representation of the relative energy (intensity) present at each frequency

harmonic spectrum

the spectrum of complex sound in which energy is at integer multiples of the fundamental frequency

fundamental frequency

the lowest frequency component of a complex periodic sound

timbre

psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar

pinna

the outer, funnel-like part of the ear

ear canal

the canal that conducts sound vibrations from the pinna to the tympanic membrane and prevents damage to the tympanic membrane

outer ear

the external sound-gathering portion of the ear, consisting of the pinna and the ear canal

tympanic membrane

the eardrum; a thin sheet of skin at the end of the outer ear canal

vibrates in response to sound

middle ear

an air-filled chamber containing the ossicles

conveys and amplifies vibration from the tympanic membrane to the oval window

ossicle

any of the three tiny bones of the middle ear

includes the malleus, incus, and stapes

malleus

the most exterior of the three ossicles

receives vibration from the eardrum and is attached to the incus

incus

the middle of the three ossicles

connects the malleus and the stapes

stapes

most interior of the three ossicles

presses against the oval window of the cochlea on the other end

oval window

the flexible opening to the cochlea through which the stapes transmit vibration to the fluid inside

inner ear

a hollow cavity in the temporal bone of the skill and the structures within this cavity

tensor tympani

the muscle attached to the malleus

tensing this decreases vibration

stapedius

the muscle attached to the stapes

tensing this decreases vibration

acoustic reflex

a reflex that protects the ear from intense sounds, via contraction of the stapedius and tensor tympani muscles

cochlea

a spiral structure of the inner ear containing the organ or corti

tympanic canal

one of three fluid filled passages in the cochlea

extends from the round window at the base of the cochlea to the helicotrema at the apex

vestibular canal

one of three fluid filled passages in the cochlea

middle canal

one of the three canals of the cochlea

sandwiched between the vestibular and tympanic canals and contains the cochlear partition

helicotrema

the opening that connects the tympanic and vestibular canals at the apex of the cochlea

stria vascularis

specialized tissue lines in one side of the middle canal and maintains the right balance of charged ions in in the endolymph to keep hair cells working at their best

reissner’s membrane

a thin sheath of tissue separating the vestibular and middle canals in the cochlea

basilar membrane

a plate of fibers that forms the base of the cochlear partition and separates the middle and tympanic canals in the cochlea

cochlear partition

the combined basilar membrane, tectorial membrane, and organ of Corti

responsible for the transduction of sound waves into neural signals

round window

a soft area of tissue at the base of the tympanic canal that releases excess pressure remaining from extremely intense sounds

organ of Corti

a structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers

auditory nerve (AN)

a collection of neurons that convey information from hair cells in the cochlea to the brainstem (afferent) and from the brainstem to the hair cells (efferent)

stereocilium

any of the hairlike extensions on the tops of hair cells in the cochlea that, when flexed, initiate the release of neurotransmitters

tectorial membrane

a gelatinous structure, attached on one end, that extends into the middle canal of the cochlea, floating above inner hair cells and touching outer hair cells

tip link

a tiny filament that stretches from the top of a stereocilium to the side of its neighbour

place code

tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition that has the greatest mechanical displacement

afferent fiber

a neuron that carries sensory information to the central nervous system

efferent fiber

a neuron that carries information from the central nervous system to the periphery

threshold tuning curve

graph plotting the thresholds of a neuron in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response

characteristic frequency (CF)

the frequency to which a particular auditory nerve fiber is most sensitive

electromotility

the ability of outer hair cells to extend and contract which changes the stiffness and sensitivity of the cochlear partition

two-tone suppression

a decrease in the response (firing rate) of one auditory nerve fiber to one tone when a second tone is presented at the same time

isointensity curve

a map plotting the firing rate of an auditory nerve fiber against varying frequencies at varying intensities

rate saturation

the point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate

rate-intensity function

a graph plotting the firing rate of an auditory nerve fiber in response to a sound of constant frequency at increasing intensities

low-spontaneous fiber

an auditory nerve fiber that has a low rate (less than 10 spikes per second) of spontaneous firing

require relatively intense sound before they will fire at higher rates

high-spontaneous fiber

an auditory nerve fiber that has a high rate (more than 30 spikes per second) of spontaneous firing

they increase their firing rate in response to relatively low levels of sound

mid-spontaneous fiber

an auditory nerve fiber that has a medium rate (10-30 spikes per second) of spontaneous firing

phase locking

firing of a single neuron at one distinct point in the period (cycle) of a sound wave at a given frequency

temporal code

tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to the period of the sound

volley principle

the idea that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but does not fire on every period

cochlear nucleus

the first brainstem nucleus at which afferent auditory nerve fibers synapse

superior olive

an early brainstem region in the auditory pathway where inputs from both ears converge

inferior colliculus

a midbrain nucleus in the auditory pathway

medial geniculate nucleus

the part of the thalamus that relays auditory signals to the temporal cortex and receives input from the auditory cortex

tonotopic organization

an arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency

primary auditory cortex (A1)

the first area within the temporal lobes of the brain responsible for processing acoustic information

belt area

a region of cortex, directly adjacent to the primary auditory cortex, with inputs from A1, where neurons respond to more complex characteristics of sounds

parabelt area

a region of cortex, lateral and adjacent to the belt area, where neurons respond to more complex characteristics of sounds, as well as to input from other senses

psychoacoustics

the branch of psychophysics that studies the psychological correlates of the physical dimensions of acoustics in order to understand how the auditory system operates

audibility threshold

the lowest sound pressure level that can be reliably detected at a given frequency

equal-loudness curve

a graph plotting sound pressure level against the frequency for which a listener perceives constant loudness

temporal integration

the process by which a sound at a constant level is perceived as being louder when it is of greater duration

also applies to perceived brightness, which depends on the duration of light

masking

using a second sound, frequently noise, to make the detection of another sound more difficult

white noise

noise consisting of all audible frequencies in equal amounts

critical bandwidth

the range of frequencies conveyed within a channel in the auditory system

conductive hearing loss

hearing loss caused by problems with the bones of the middle ear

otitis media

inflammation of the middle ear, commonly in children as a result of infection

otosclerosis

abnormal growth of the middle-ear bones that causes hearing loss

sensorineural hearing loss

hearing loss due to defects in the cochlea or auditory nerve

metabolic hearing loss

hearing loss caused by degraded ability of the stria vascularis to provide sufficient nutrients and ions to the cochlear partition

presbycusis

age-related hearing loss