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Hearing

Terms in this set (54)

transduction
conversion of one form of energy to another
i.e. mechanical to electrical; chemical to electrical
pinna
part of the ear on we can see on the outside of the body
ear canal
tube leading from the pinna to the middle ear
external ear
pinna and ear canal
amplitude
sound pressure, which we perceive as loudness
frequency
number of cycles of vibration per second, which we perceive as pitch
middle ear
the cavity between the tympanic membrane and the cochlea
tympanic membrane
aka eardum. taut membrane that serves as a partition between the external ear and the middle ear
ossicles
three small bones (malleus, incus, and stapes) that transmit and concentrate sound across the middle ear from the larger tympanic membrane to the smaller oval window
oval window
the opening from the middle ear to the inner ear
tensor tympani
muscle attached to the malleus that modulates mechanical linkage to protect the delicate receptor ells of the inner ear from damaging sounds; also helps attenuate self-made sounds.
stapedius
middle ear muscle attached to stapes. Helps prevent damage from loud sounds by contracting and helps attenuate self-made sounds.
inner ear
consists of cochlea and vestibular apparatus
cochlea
snail-shaped structure in the inner ear that contains the primary receptor cells for hearing. converts vibrational energy into waves of fluid. embedded in temporal bone of skull. consists of three parallel canals filled with non compressible fluid: scala vestibuli, scala media, and scala tympani. oval window is next to the base, where the canals and membranes are narrow and high frequencies have their greatest effect. the apex is the distant wide end where low frequencies have their greatest effect.
round window
membrane separating cochlear duct from the middle ear cavity. it can bulge out a little in response to movement inside the cochlea
organ of Corti
structure in the inner ear that lies on the basilar membrane of the cochlea and contains the hair cells and terminations of the auditory nerve.
basilar membrane
base of the organ of Corti, which contains the principal structures involved in auditory transduction. it vibrates in response to sound
hair cells
two sets within the organ of Corti: IHCs and OHCs. each of these cells has 50-200 stereocilia protruding
tectorial membrane
a membrane on top of the organ of Corti in the cochlear duct. stereocilia of OHCs extend into indentations on this membrane.
stereocilia
relatively stiff hairs that protrude from hair cells in the auditory or vestibular system. sounds that cause these hairs to sway increase tension on the tip links, causing their ion channels to open, letting in calcium and potassium and depolarizing the whole hair cell. the channels then snap shut like a trapdoor when the hair sways back. the action potentials generated here reach the brain via the vestibulocochlear nerve (cranial nerve VIII).
tip link
fine threadlike fiber that runs along and connects the tips of stereo cilia. play a key role in the generation of hair cell potentials.
synapses of the organ of Corti
IHCs (have more nerve fibers associated)
Afferent: to cochlear nucleus of brainstem (give rise to sound perception)
Efferent: from lateral superior olivary nucleus

OHCs
Afferent: to cochlear nucleus
Efferent: from medial superior olivary nucleus

The nerve fibers synapse on the base of hair cells.
outer hair cells
change length to fine tune/discriminate between sounds with a difference as little as 2 Hz. hyperpolarization causes them to lengthen, while depolarization causes them to shorten. causes fragments of basilar membrane to stiffen or relax, sharpening tuning. also produces otoacoustic emission.
otoacoustic emissions
sound produced by the cochlea itself when it pushes back on the eardrum, either spontaneously or in response to an external noise.
tuning curve
a graph of the responses of a single auditory nerve fiber to sounds that vary in frequency or intensity. a fiber's "best frequency" is the one at which the amplitude threshold for response is the lowest. fibers respond to many different frequencies, but with different sensitivities.
vestibulocochlear nerve
cranial nerve VIII, which runs from the cochlea to the brainstem auditory nuclei.
cochlear nuclei
brainstem nuclei that receive input from both right and left cochlear nuclei. outputs to superior olivary nuclei and inferior colliculi.
binaural
referring to simultaneous processing based on auditory inputs of both ears
superior olivary nuclei
brainstem nuclei that receive projections from the right and left cochlear nuclei and provide the first binaural analysis of auditory information, which plays a key role in sound localization.
inferior colliculi
paired gray matter structures of the dorsal midbrain that receive auditory inputs from cochlear nuclei. they are the primary auditory centers of the midbrain. projections to medial geniculate nuclei of thalamus.
medial geniculate nuclei
nuclei in thalamus that receive input from the inferior colliculi and send output to the auditory cortex. neurons can be excited by certain frequencies and inhibited by neighboring ones, furthering sharpening frequency responses.
tonotopic organization
a major organizational feature in auditory systems in which neurons are arranged as an orderly map of according to the auditory frequencies to which they respond, with cells responsive to high frequencies located at a distance from those responsive to low frequencies.
minimal discriminable frequency difference
the smallest change in frequency that can be detected reliably between two tones. the detectable difference is about 2 Hz for sounds up to 2000 Hz, above that a larger difference is required.
place coding
hypothetical mechanism that accounts for discrimination between pitches - the encoding of a sound frequency as a function of the location on the basilar membrane that is most stimulated by that sound. basically, activation of receptors at the cochlea's base signals treble, and activation of receptors at the apex signals bass.
temporal coding
hypothetical mechanism that accounts for discrimination between pitches - the encoding of sound frequency in terms of the number of action potentials per second produced by an auditory nerve. Firing of the action potential is phase-locked to the stimulus - it rate of firing directly reflects number of cycles per second (frequency)
intensity differences
perceived differences in loudness between the two ears, which can be used to localize a sound source. at low frequencies, however, there is no difference in perceived intensity no matter where the sound is coming from.
latency differences
differences between the time of arrival of a sound for each ear, which can be employed by the nervous system to localize the sound source
duplex theory
a theory stating that we localize sound by combining information about intensity differences and latency differences between the two ears
sound shadow
refers to the head blocking the path of sound waves to one of the ears, so the waves have to take a longer path. contributes to latency differences.
onset disparity
the difference between the two ears in hearing the beginning of the sound. type of latency difference.
ongoing phase disparity
the continuous mismatch between the two ears in the arrival of the peaks and troughs of the sound wave. type of latency difference.
coincidence detector
senses the co-occurence of two events - in birds, binaural neurons in the nucleus laminaris are maximally excited by a parti ulnar latency difference between inputs form the two ears, corresponding to a particular place in space. this map of auditory space is further developed in the bird's tectum.
sound localization in mammals
unlike birds, these animals use the superior olivary nucleus as the primary sound localization nucleus. the lateral superior olive (LSO) processes intensity differences and the medial superior olive (MSO) processes latency differences - but it does not contain a map of auditory space. sound location is actually encoded by the relative activity of the entire left MSO with the entire right MSO.
spectral filtering
alteration by the shape of the external ear of the amplitude of some, but not all, frequencies in a sound as the waves are funneled into the ear. the frequencies that are affected depend on where the sound originates. these cues provide information about the vertical location of the sound.
hearing loss
decreased sensitivity to sound, in varying degrees
deafness
hearing loss so profound that speech perception is lost
conduction deafness
hearing impairment arising from disorders in the external or middle ears that prevent vibrations from reaching the cochlea. nervous system is generally not involved in this type of deafness. ex - ossicles become fused
sensorineural deafness
hearing impairment originating from cochlear or auditory nerve lesions in which auditory nerve fibers cannot excite normally. usually permanent. can be caused by defects in genes encoding hair cell structure and function. ex - mutation in GJB2 gene, which encodes formation of electrical synapses (gap junctions)
ototoxic
toxic to the ears
tinnitus
sensation of noises or ringing in the ears resulting from hearing noises that are too loud
central deafness
hearing impairment related to lesions in auditory pathways or centers, including sites in the brainstem, thalamus, or cortex.
word deafness
disorder in which sounds can be detected, but words can't be heard or recognized
cortical deafness
hearing impairment caused by bilateral lesions in auditory cortex (rare), resulting in difficulty recognizing both verbal and nonverbal auditory stimuli. can be caused by a stroke.
cochlear implant
electromechanical device that detects sounds and selectively stimulates nerves in different regions of the cochlea via surgically implanted electrodes. this is possible because even if hair cells are damaged, the auditory nerves are still excitable.
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