A
oval window
a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear
cochlea
coiled and channeled main structure of the inner ear. contains three fluid-filled canals that run along its length. the fluid-filled canals are separated by membranes, one of which is the basilar membrane
stereocilia and kinocilium
- stereocilia - projections at the top of the hair cell, attached to one another by structures linking the tips of the cilium. moving tip links may open an ion channel and produce the receptor potential in the hair cell
- kinocilium - one larger, more stable cilium to which the stereocilium attach at the tips
cochlear implant
surgically implanted electronic device that creates neural signal through electrodes implanted along basilar membrane; requires auditory nerve fibers to be intact, hair cells just not functioning → resolution not as good as hair cells are
inferior colliculus (IC)
located just below the visual processing centers known as the superior colliculus. tonotopically organized, likely integrates info regarding sound localization. projects to the thalamus (MGN) and cortex.
What is the pathway of sound through the ear?
sound enters pinna (outer ear) → tympanic membrane → ossicles → vibrate oval window → cochlear fluid movement in inner ear → agitates cilia in basilar membrane
basilar membrane
important for transduction of sound from air to fluid wave → membrane has different physical properties from base to tip, lets us encode different sound frequencies
- base: stiff and narrow, easy to move by higher frequency tones
- tip/apex: wider and more flexible, easier to move by lower frequencies
outer hair cells
modulates incoming sound (acoustical pre amplification) → extends frequency range, improves frequency discrimination
outer hair cells do not directly transduce sound pressure waves to neural signals
cochlear nucleus
group of cell bodies in the lower section (medulla) of the brainstem that receives the inputs from all the auditory nerve fibers coming from the cochlea
medial geniculate nucleus (MGN)
section of thalamus that the auditory pathway connects to before reaching A1. relays details of sound to cortex, detects relative intensity and duration of sound, tonotopic organization, projects to primary auditory cortex (auditory core)
conductive hearing loss
issues in conducting external sound into inner ear; sound vibrations can't be transferred to cochlea
- causes: blockage in the ear canal, ruptured eardrum, or restriction of the movement of ossicles
tonotopic organization
map of tones: Each section of the basilar membrane responds to a preferential frequency and the sections are organized from high to low. Tonotopic organization is also seen in the cortex as tonotopic gradients (organized cortical representations of tones).
sensorineural hearing loss
mild-to-total hearing loss due to issues in vestibulocochlear nerve, inner ear, or central processing centers of brain → cilia loss common
- causes: genetic, acquired (ex: loud noises rip proteins off the cilia, disconnecting them)
- treatments: hearing aids
what is superior olive
what is medial superior olive
small group of cell bodies in middle section (pons) of brainstem. receives binaural inputs (inputs from both ears), where left/right sound localization occurs (sound's intensity and timing)
medial superior olive: responsible for interaural time difference (time difference of arrival of sounds between the ears)
lateral sulcus
aka Sylvian fissue or lateral fissure. sulcus that divides the frontal and temporal lobes of the brain. primary auditory cortex (A1) is located within the lateral sulcus.
otosclerosis
form of conductive hearing loss. abnormal growth on ossicles, causing joints to become very stiff → unable to properly bend/move to amplify tympanic membrane movement onto oval window
- causes: starts in middle age. no exact cause, maybe genetics, viruses
- treatments: hearing aids, surgery to remove stapes
inner hair cells
turns sound to neural signal (fires more when sounds occur, less as sound goes away), very high acuity (many auditory nerve fibers per cell)
superior temporal sulcus
most superior sulcus in the temporal lobe, just below the superior temporal gyrus
auditory agnosia
rare form of agnosia where patients can physically hear sounds and describe them, but are unable to recognize them. not an ear or hearing defect, is a neurological inability of the brain to process sound meaning
caused bilateral damage to anterior temporal lobes (responsible for sound recognition, the auditory "what" pathway)
superior temporal gyrus
most superior gyrus in the temporal lobe, situated just below the lateral sulcus, on which is much of auditory cortex
inner ear
from oval window to auditory nerve; includes oval window, round window, cochlea, auditory nerve fibers, and the semicircular canals of the vestibular system
cilia
hairlike projections inside basilar membrane. first auditory receptors to send info to auditory nerve fibers as tectorial membrane tilts them.
tips have ion channel gates and are connected to each other w/ protein molecules → hairs bend, opening/closing channel, allowing cell to either depolarize or hyperpolarize
tonotopy, periodotopy
- tonotopy - cortical map of sound frequency (single tones)
- periodotopy - cortical map of sound time duration (periodicity)
lateral superior olive
responsible for interaural level difference (difference of intensity level/volume of sounds between the ears)
primary auditory cortex (A1)
main area of cortex that first processes auditory info in the brain, situated on the inferior surface of the lateral sulcus; contains core, belt, and parabelt subdivisions. Each subdivision contains multiple auditory field maps.