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Auditory system have...
tonotopic basis for frequency coding along the length of cochlea and the tympanic membrane
the tympanic membrane does what?
transduced info to neural signals
Hearing (sounds) are...
waves of compressed air traveling thru space
sound intensity is
the sound wave height
the wave frequency
organ of hearing (and equiliibrium) is where?
in the inner ear where the cochlea and the vestibular apparatus located
pathway sensory ograns. hearing.
- -sound waves enter the external auditory canal and trigger vibes of tympanic membrane
- -tympanic membrane induces a vibe of the ossicles
- -last ossicle, (stapes) transmit amplified vibrations to oval window
- -vibes induce waves in perilymph of various inner ear chambers
- -round window absorbs excess energy and prevent wave reverberation
- -fluid wave is transduced into electrical signal by auditory receptors, organs of corti located on basilar membrane
where are receptors for sound?
the organ of Corti
Organ of Corti
- have hair cells that transduce fluid wave to electrical signal
- -energy of wave causes basilar and vestibular membrane to move, displacing hte cilia from organ of Corti
movments of the cilia does what to the what channels?
- open or close potassium channels
- also changes state of polarization of hair cell
changes in potassium leakage is due to?
cilia bending, which triggers changes in neurotransmitters exocytosis
neurotransmitters sends what to where?
electrical signal to afferent neuron of the cochlear nerve
Louder the sound,
more the cilia bend, more AP produced
which or wher is the membrane responsible for pitch
Organs of Corti, which is located near the oval window (more sensitive to high pitch sounds while tip of cochlea respond to love pitch sound)
neural pathways for sounds
cochlear nerve ==> nucleus in medulla oblongata ==> thalamus ==> auditory cortex in temporal lobe
3 major auditory relay nuclei of brainstem.
- cochlear nuclei (same as cn VIII in medulla)
- superior olivary nuclear complex (integration from both side in pons - important in sound localization major input from AV cochlear nucleus)
- inferior colliculus (in midbrain)
two audtiory systems..
- anteroventral cochlear n.
- dorsal posterior ventral cochlear n.
anteroventral cochlear n
- superior olivary n. (both sides) ==> lateral lemniscus ==>inferior colliculus
- important for horizontal location of sounds as well as sound patterns
dorsal posteriorventral cochlear n.
- lateral lemniscus to inferior colliculus (opp side)
- important for integration
What notices the difference between low and high frequency?
superior olivary n. (medial and lateral)
low fre sounds distinguished in space by?
interaural time difference
high fre sounds distinguished by
difference in intensity between ears
decussation of auditory nuclei visible in where?
olivocochlear bundle regulates?
flow of auditory info to brain
most auditory path neurons cours in lateral lemniscus in where?
some synapse on nucleus of lateral lemniscus where?
contralateral inferior colliculus
important site of decussation of the lateral lemniscus
where is the inferior colliculus
- the midbrain tectum
- -central nucleus receives auditory info, which proceed to medial geniculate nucleus of thalamus and primary auditory cortex
- -neurons in single lamina max. sensitive to similar tonal freq
- -receives input from superior olivary n, n. of lateral lemniscus (both sides) and dorsal n. with pv cochlear (direct)
- -project to thalamus thru brachium of inferior colliculus
Medial geniculate nucleus
- thalamic auditory relay nucleus
- -major part (ventral division) is tonotopically organized (receives input from central n. of inf coll, which is also tonotopically organized)
- -MGN also linated - layers max sensitive to similar frequencies
- -thalamocortical auditory projections (aka auditory radiations)
medial geniculate nucleus have columnar organization of neurons sensitive to...
- tones of similar freuqencies (isofrequency columns)
- -binaural columns (interaural intensity differences for localization of high-freq. sounds
- -have prominent layer 4
- higher order auditory cortex for the interpretation of language
- (lang. on L side of brain; interpreting emotional content of lang on R side)
- -one projection to broca's motor speech area in frontal lobe
deals with the sensory organs: vestibular
- ampulae of semicircular canals
- -Maculae of utricle (linear acceleration) + saccule
- and endolymph
gel-like fluid flows over hair cells with movement and deflects them (Ca carbonate crystals ...otoliths)
equilibrium of the semicircular canals
- ability to detect head position and movment (or acceleration)
- -change of speed (linear acceleration
- -turning (rotational acceleration)
What detects thhe change of speed?
utricle and saccule
what detects turning?
what detects backward-frontward movement?
what detects change relative gravity?
sensory cells have cilia extending into gelatinous material topped by...
receptors in ampulla
- are hair cells with cilia extruding itno gelatinous mass (cupula)
- -when head rotates, cupula moves, cilia pulled, APs(vestibular nerve, to cerebellum
where is the vestibular nuclei located?
- floor of 4th ventricle
- 4 nuclei: inferior, medial, lateral, superior
- à ascending projections to VPN of
- thalamus à 1° vestibular cortex in parietal
- lobes (just behind the 1° somatic sensory cortex).
- Can project to nearby parietal areas for integration of info regarding head motion
- with info from somatic sensory receptors in trunk and limbs.
Head motion is due to?
cell receptors of the vestibular system?
- 4 vestibular n. in rostral medulla and caudal pons
- -2 descending projec. to sc and extraocular muscles (control movements) to cerebellum
-2 ascending proj. VPN to thalamus to primary vestibular cortex in parient lobe (for conscious awareness of orientation and motion)
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