Hearing Smell Taste Lecture- Hearing Flashcards
Soundwaves
Amplitude
- measured as sound pressure
- =loudness
- Height of a wave as measured from the peak to the trough
Sound waves
Frequency
- measured in Hertz (Hz)
- frequency = pitch
- most peoplel detect 20-20,000 Hz
- increases amount of waves per unit time
How does the brain interpret sound?
Mechanical energy of sound waves transducted into neuronal electrical activity
What is sensory transduction?
the conversion of energy from a stimulus into a change in membrane potential
Outer ear
What is the pinna’s function?
The pinna funnels sound waves into the ear canal
How does sound travel from air to ear?
- once the pinna funnels sound waves into the ear canal, sound waves progagate down the canal to the tympanic membrane (aka ear drum)
the tympanic membrane separates the outer ear from the middle ear
middle ear
What happens after sound waves reach the tympanic membrane?
- vibrations in the tympanic membrane cause 3 ossicles (malleus, incus and stapes) to move
middle ear
What are ossicles?
- tiny bones in the middle ear that serve to transmit sounds from air to cochlea
- absence would constitute a moderate to severe hearing loss
middle ear
What do the Tympani and Stapedius muscle do?
- control contact between ossicles to protect from loud sounds
- also mute self-made sounds (ex. swallow)
middle ear
Where is the stapedius muscle located?
- Stapedius muscle is caudal/inferior to the stapes bone
inner ear
What does the stapes contact? What is the function of this?
- stapes contacts the oval window
- the oval window transfers vibrations to 3 fluid filled canals in cochlea
inner ear
What does the cochlea look like?
small and coiled
inner ear
What separates the cochlea’s canals?
the basilar membrane
inner ear
Basilar membrane function
- Vibrates- Different areas are sensitive to specific frequencies
- high freq at narrow stiff base (when cochlea unrolled)
- low freq at wide, floppy apex (when cochlea unrolled)
What is a tonotopic map?
an ordered map of frequencies created by the responding of neurons within structures in the auditory system
inner ear/tuning curves of hair cells
Where are hair cells located?
on the thin basilar membrane in the cochlea of the inner ear
What do hair cells have?
- distinctive receptive fields, or tuning curves
- a tuning curve provides a three dimensional plot of the firing rate of hair cells over a restricted range of stimulus frequencies and intensities
The more sensitive the hair cell…?
the greater the response (as visualized on tonotopic map of frequency!)
cochlea
What does the Organ of Corti contain and where is it found?
- located on basilar membrane (sits on top)
- contains inner and outer hair cells
What do inner hair cells do? Where are they located?
- they detect sound
- part of organ of corti
- superior to nerve fibers
- to right of outer hair cell (closer to the brain)
What do outer hair cells do?
- amplify low-level sounds to help discriminate between similar frequencies
- located more outside than inner hair cells in regards to brain location
cochlea- organ of corti
Together, what do hair cells do?
- transduce sound waves into neuronal activity
- synapse with auditory nerve fibers
- have 50-200 stereocilia (hairs required for hearing and balance)
What are tip links? Where are they located and what do they do?
- Tip links are extracellular tethers that link sterocilia
- They open ion channels when sterocilia are bent
Transduction of sound into electrical transmission
- On the inner hair cells, vibrations bend/displace sterocilia
- tip links open ion channels
- Ca2+ and K+ depolarize inner hair cell
- Glutamate is released onto auditory nerve
Pathway from hair cells to brain
- Hair cells synapse onto vestibulocochlear nerve (8th)
- 8th nerve synapses onto cochlear nucleus in brain stem
- Info travels to both superior olivary nuclei (most info crosses midline)
- Inferior colliculus (primary auditory centers of midbrain), then medial geniculate nucleus (thalamus), then auditory cortex
inferior colliculus
- tonotopic map- critical for sound localization
- procsses intensity, frequency, and duration of sound
auditory cortex function
- identifies complex sounds that have many sub-parts (eg vocalizations)
- tonotopic map (corresponds to apex to base of cochlea as you move caudally
Where is the primary auditory cortex located?
temporal lobe
conduction deafness
disorders of the outer/middle ear that prevent vibrations from reaching the cochlea
sensorineural deafness
originates from cochlear or auditory nerve lesions; hereditary disease of hair cells
What is central deafness?
hearing loss caused by brain lesions (such as stroke) with complex results
Pathway to brain
What do hair cells synapse onto?
- the vestibulocochlear nerve (8th)
- located on the cochlea
pathway to brain
What does the 8th nerve synapse onto?
- the cochlear nucleus in the brain stem
pathway to brain
What happens after info travels to the cochlear nucleus?
- it travels to both superior olviary nuclei
- most info crosses the midline
After reaching both superior olivary nuclei, where does info go?
- to the inferior colliculus (primary auditory centers of midbrain)
- then to the medial geniculate nucleus (thalamus)
- then to the auditory cortex (temporal lobe)
where is the medial geniculate nucleus located?
the thalamus
Where is the inferior colliculus located?
midbrain (is the primary auditory center of the midbrain)
What are the three ossicles?
- malleus
- incus
- stapes
