unit 4a Flashcards
auditory disorders
Sound pressure wave
sound= mechanical wave that results f/ back & forth vibration of particles of the medium thru which the sound wave is moving
- if a sound wave is moving f/ left → right thru air, then particles of air will be displaced both right/left~ward as the energy of sound wave passes thru it. Motion of particles is parallel (& antiparallel) to the direction of energy transport
- a sine wave can be used to encode info abt the compression & rarefaction (expansion) of sound pressure waves
– Increases of the physical properties of FREQUENCY f/ low → high are assoc w/ incr. in the perceptual exp. of PITCH
–Increases of the physical property of AMPLITUDE f/ sml to log (blue arrow) are assoc. w/ incr. in the perceptual exp. of LOUDNESS
–Wavelength stays constant over distance, but AMPLITUDEof sound pressure wave DECREASEs
→ The energy contained in sound pressure wave is lost as the sound pressure propagates thru the atmosphere. As a result the amt of compression & rarefaction (amp. of wave) decr. over distance, but the timing of the compression & rarefaction (freq.) does not
Audibility curve
a graph that depicts the relat. b/t the loudness of a pure tone, expressed in decibels, sound-pressure lvl (dB SPL), & the freq. of the tone
Outer ear
incl. the pinna (AKA auricle) + auditory canal & ends at the tympanic membrane
Pinna: consists of cartilage covered by skin & shaped to capture sound waves + funnel them thru ear canal → tympanic membrane
-important in localizing sounds f/ front v. back & helps w/ vertical sound localization (ex: sound is higher/lower)
Ear Canal: directs the sound pressure wave onto tympanic membrane & amplifies sounds that are b/t 3-12 kHz.
Tympanic membrane
(AKA eardrum)
thin membrane that separates the external ear f/ the middle ear
Function: transmit sound f/ air to the ossicles inside middle ear
Middle ear
f/ tympanic membrane → oval window: incl. the ossicles & frames out thru the eustachian use to the back of the throat
Ossicles
AKA auditory ossicles
3 smallest bones in body. Contained w/in the middle ear space & serve to transmit & amplify sounds f/ air → fluid-filled cochlea. Absence of auditory ossicles would constitute a moderate-severe hearing loss
Bones: Malleus, Incus, Stapes
Malleus
the malleus/ hammer is a hammer-shaped small bone/ossicle of the middle ear
- connects w/ the incus & is attached to the inner surface of the eardrum
Incus
the incus/anvil is an anvil-shaped small bone/ossicle in middle ear
- Connects the malleus to the stapes
Stapes
Stapes/stirrup is stirrup-shaped small bone/ossicle in the middle ear which is attached to the incus & oval window
- the bottom of the stapes on the oval window is called the FOOTPLATE
Oval window
A membrane-covered opening which leads f/ the middle ear to the vestibule of the inner ear
Conductive hearing loss
mechanical hearing loss, resulting f/ blockage in the ear canal, ruptured eardrum, restric. of mvmt of the ossicles, which prevents sound vibrations being transferred to the cochlea
- seen in otosclerosis
Otosclerosis
a form of conductive hearing loss
a condition in which there is abnormal growth of bone in middle ear which can result in hearing loss
-seen in 0.5%-10% of pop., usually starts in middle age
-exact cause is unclear
→ genetic factors play a role, viruses like measles may be involved
-treated w/ hearing aids &/or surgery to remove stapes
Inner ear
f/ oval window to auditory nerve
-incl. oval window, round window, cochlea, auditory nerve fibers, & the semicircular canals of the vestibular system
Cochlea
the coiled & channeled Amin structure of the inner ear
incl. 3 fluid-filled canals that run along its entire convoluted length
- the fluid filled canals are separated by membranes, one of which is the basilar membrane - which 1000s of hair cells (auditory receptors) are arranged & stimulated by vibration of the stapes
Basilar membrane
w/in the cochlea
a stiff structural element that separates 2-liquid filled tubes (the Scala) that run along the coil of the cochlea, - forming a base for hair cells to transduce the sound waves in the cochlear fluid to electrochemical signals in the brain
Tonotopic organization
map of tones:
Each section of basilar membrane responds to preferential freq. & the sections are org. f/ high to low.
- Tonotopic org. is also seen in cortex as tonotopic gradients (org. cortical repr. of tones)
Inner hair cells
the sensory receptors of the auditory system
- located on basilar membrane in the cochlea
-convert sound waves to nerve signals by having their hair-like stereocilia being physically moved by sound waves in the cochlear fluid
Hair cells are columnar ells, each w. a bundles of 100-200 specially stereo cilia at the top. these cilia are mechanosensors for hearing. Lightly resting atop of longest cilia is the TECTORIAL MEMBRANE, which moves back/forth w/ each cycle of sound, tilting cilia & allowing electric current into hair cells
→ Hair cells show graded response, instead of spikes typical of other neutrons
Loud noise can damage/destroy hair cells, (do not regrow). Continued exposure to loud noise causes progressive damage, eventually resulting in hearing loss & sometimes ringing in ears (tinnitus)
Stereocilia & Kinocilium
Stereocilia: projections @ top of the hair cells that are attached to one another by structures which link the tips of 1 cilium to another
- stretching & compressing the tip links may open an ion channel & produce the receptor potential in the hair cell
Kinocilium: one larger, more stable cilium to which stereo cilium attach at the tips
Outer hair cells
hair-like cells on basilar membrane
-involved in amplifying sounds & improving frequency selectivity:
only found in mammels
Although there are nearly 3x more outer hair cells than inner hair cells, outer hair cells dont directly transduce sound pressure waves to neural signals
Organ of Corti
the organ in inner ear of mammals that contain the hair cells ( auditory sensory cells)
Transduction occurs thru vibrations of structures in the inner ear causing displacement of cochlear fluid & mvmt of hair cells @ the organ of Corti → to produce electrochemical signals that activate auditory never fibers synapsing on the inner hair cells.
Sensorineural hearing loss
hearing loss caused by damage to sensory cells and/or nerve fibers of the vestibulocochlear nerve (auditory nerve/ cranial nerve VIII), inner ear, or central processing centers of the brain
- seen in many forms of congenital & acquired deafness
Cochlear implant
a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severe hard of hearing.
Most commonly, used when hair cells of patient are damaged/developed w/ a genetic abnormality affecting action potentials
In order for implant to work, auditory nerve fibers (along the basilar membrane) must still be intact, as the electrodes of implant serve to activate these auditory nerve fivers
Cochlear nucleus
a grp of cell bodies in lower section (medulla) of brainstem
- receive the inputs f/ all auditory nerve fibers coming f/ cochlea
Superior olive
a small group of cell bodies (nucleus) in middle sections (pons) of the brainstem involved in localization of sound by determ. diff. in the timing (MEDIAL superior olive) & intensity/lvl (LATERAL superior olive) of neural responses f/ each ear for a particular sound
