ear and auditory pathways Flashcards
define sound, frequency and pitch
sound- transverse wave of compressed and rarefield air frequency is pitch, amplitude is volume
ear anatomy- outer, middle and inner ear DIAGRAM
outer ear cartilaginous, made out of pinna (auricle) and auditory canal (acoustinc meatus), ending at tympanic membrane middle ear between tympanic membrane and oval window, with ossicles (malleus, incus+ staples) inner ear is cochlea and vestibular apparatus
amplification of sound
sound goes through canal to tympanic membrane, then to malleus, incus, stapes and oval window, creating pressure wave in FLUID of cochlea lever system of ossicles and larger SA of tympanic membrane to oval window amplifies sound
how ear is protected
too much vibration can damage hair cells- thus reflex contraction of TENSOR TYMPANI and STAPEDIUS reduces leverage through ossicles- good for natural sounds, NOT MAN MADE auditory tube connecting middle ear with nasopharyx helps equilibrate air pressure either side of tympanic membrane as well
anatomy of cochlea and sound transduction DIAGRAM- is endo or perilymph higher in K+
once sound hits oval window, they go to SCALA VESTIBULI and then SCALA TYMPANI- it travels up reissners/vestibylar membrane, creating pressure wave in scala media- then goes across basial membrane and joins pressure wave in scala tympani
reissner and basilar membrane divide cochlea into these 3 regions- scala media contains endolymph (HIGH in K+), the ohter two contain perilymph
organ of corti DIAGRAM
in inner ear with sensory hair cells- they have stereocilia bathed in ENDOLYMPH which touch the tectorial membrane (doesn’t vibrate)- basilar membrane however does vibrate
role of scala media DIAGRAM
lined by stria vascularis, which produce endolymph to maintain a high K+ conc.
modiolus DIAGRAM
bone structure where spiral ganglia from CN8 are present- base of hair cells at basilar membrane send impulses to axons of CN8 - impulses travel to spiral ganglia in modiolus, then to vestibulocochlear nerve, then brainstem
cochlear hair cells
they have projections called stereocilia on apical surface, and synapse with CN 8 axons at basilar end- movement of stereocilia sends impulses down these axons
inner vs outer hair cells including functional difference
therea are more outer hair cells (single row of inner hair cells followed by triple row of outer)- both innervate by spiral ganglia, but inner more densely innervated inner cells provide auditory info to brain, outer cells needed for refining
what stereocilia do DIAGRAM
their movement causes opening of K+ channels- in upwards phase, movement causes basilar membrane to go up and hair cells move away from modulus= K+ channel open= Ca2+ open= glutamate release= A.P in hair cell, then spiral ganglion
in downwards phase, opposite occurs and hair cell hyperpolarises
stereiocilia and tiplinks DIAGRAM
increase in length the further away from the modiolus, with their tips connected by tiplinks in upwards phase- greater distance between tiplinks, so more tension, opening K+ channels- this distance decreases in downwards phase
frequency perception DIAGRAM
basilar membrane is HETEROGENOUS, so only a certain region of membrane will vibrate depending on the frequency (like a xylophone)- thus brain can tell between different frequencies lower frequencies cause vibration near apex (membrane wider and more flexible), higher frequency near base
central auditory pathway DIAGRAM
cochlear nerve (part of CN8) takes impulses from cochlea to cochlear nucleus, then to superior olive AND the OTHER SUPERIOR OLIVE- means that info from one ear goes to both pathways, so hearing loss on one side can only be due to cochlear nerve or ear problem info then sent to inferior colliculus, then medial geniculate body in thalamus, then auditory cortex in temporal lobe
tonotopic mapping and secondary auditory cortex DIAGRAM
primary auditory cortex has different regions to for different frequencies- secondary auditory cortex helps respond to more COMPLEX sound patterns
