SDL Auditory System Flashcards
the lowest sound pressure a human can hear
2000 Hz
humans can hear a sound at a different frequency other than 2000 Hz, but the sound intensity..
must be higher
intensity equation
I = 20 log P/R
so, a sound that is 10 x louder is 20 dB louder
sound pressure level of normal speech
60 dB
what happens when sound enters the external auditory meatus?
it hits the tympanic membrane, which initiates the movement of ossicles
where is the sound transmitted after relaying through the ossicles?
from the tympanic membrane to the oval window
what is the significance of the tympanic membrane being larger than the oval window?
transforming a small force into a large one, called “impedance matching”. gives a 10-fold increase of force/area through this process
the force of impedance matching is used to…
push perilymph in the inner ear
muscles attached to ossicles, and that cranial nerves innervate them
tensor tympani - CN V
stapedius - CN VII
function of tensor tympani and stapedius; what happens to hearing when CN VII is damaged?
reflex contraction of these muscles helps protect hearing apparatus during sustained loud sounds.
if CN VII is damaged, the stapedius will malfunction, and normal sounds will sound very loud AKA “hyperacusis”
movement of perilymph waves from start to finish
immediately outside the oval window in the scala vestibule, around the helicotrema, and in the scala tympani (all in the cochlea)
characteristics of endolymph and perilymph
endolymph: like intracellular fluid, high in K+
perilymph: like extracellular fluid, high in Na+
the compartment filled with endolymph
cochlear duct (scala media)
apparatus designed to detect sound//location
organ of Corti; sits inside the cochlear duct on the basilar membrane
location of inner and outer hair cells and their function
sit on the basilar membrane and touch the tectorial membrane/ responsible for detecting sounds
how is the sound wave (vibration) transformed to electric signals in the auditory system?
sound waves hit tympanic membrane, vibration transmitted into cochlea causing waves in perilymph/endolymph and movement of basilar membrane
hair cells move
stereocilia on top of hair cell touches tectorial membrane, bent toward one direction or another
this increases glutamate release from the hair cell while bending toward the other direction will decrease glutamate release
glutamate will activate the primary auditory neurons of the spiral ganglion. series of action potentials will then be initiated.
the spiral ganglion receives most of the inputs from the..
inner hair cells; outer hair cells help increase sensitivity of the inner hair cells
shape of the basilar membrane
narrow at the base, wide at the apex
type of sound that moves through the apex of the basilar membrane (wider, more flexible)
low frequencies; hair cells are tuned to low frequencies here; apex=low tones
the base of the basilar membrane is narrower and stiffer, equipped for..
higher tones
loss of hair cells can be caused by..
excessive loud noise
aminoglycoside antibiotics toxicity - neomycin, kanamycin, streptomycin, gentamicin
aminoglycosides can cause hair cell in which systems.
auditory and vestibular system
how auditory info is sent to the brainstem
hair cells release glutamate, stimulates the primary auditory neurons of the spinal ganglion, info sent via the cochlear nerve, to the cochlear nuclei in the medulla
once the auditory info enters medulla and goes beyond the cochlear nuclei, how does it ascend in the brainstem? what structure?
ascends bilaterally- the trapezoid body is a set of fiber bundles that transmits auditory signals from side to side.
because of the bilateral distribution of fiber bundles that transmit auditory signals, a unilateral lesion of the brainstem..
does NOT cause apparent hearing deficit
a lesion that occurs distal to the cochlear nuclei will cause..
ipsilateral hearing deficit
the major fiber bundle ascending with the auditory info
lateral lemniscus
major components of the auditory system, where they’re located
inferior colliculus (midbrain), medial geniculate nucleus (midbrain)
the destination of auditory info
transverse temporal gyrus
location of cochlear nucleus
medulla
auditory pathway starting with organ of corti
organ of corti, spiral ganglion, cochlear nuclei, lat lemniscus, inferior colliculus, brachium, medial geniculate nucleus, internal capsule, auditory radiation, primary auditory cortex, transverse temporal gyrus, broadman’s area (41, 42)
a structure that helps us to localize the source of a sound, from left or right side of the body
superior olivary nucleus
how does the superior olivary nucleus localize sound from the left or right side of the body?
the sound going to the opposite side of the body’s ear will have a lower intensity; the superior olivary nucleus on the left and right sided pons will compare the sound info from each ear and determine the source of the sound
structure that does selective attention of sounds in a setting with multiple noise levels going simultaneously; mechanism?
efferent cochlear bundle; signals from the superior olivary nucleus is rerouted to the organ of corti to suppress irrelevant auditory signals (normally info Is sent from organ of corti to superior olivary nucleus)
what causes perilymph fistula?
a leak of perilymph through the oval window or round window; change in air pressure could aggravate this situation (flying, scuba diving)
where in the brain is the auditory cortex?
transverse temporal gyrus Heschi
tests used to determine conduction hearing loss or nerve hearing loss
Weber test, Rinne test
what is the functional difference between lateral leminuscus and medial lemniscus?
lateral - auditory
medial - vision
what is the difference between superior colliculus and inferior colliculus?
superior does vision, inferior does auditory
difference between medial geniculate nucleus and lateral geniculate nucleus?
LGN - vision
MGN - auditory
does the auditory pathway go through the thalamus?
yes
which structures in the auditory pathway belongs to thalamus?
medial geniculate nucleus
