Exam 2 Material: Hearing Flashcards
What is sound created by?
pressure waves in the air
amplitude
loudness, expressed in decibels (dB)
How many decibels is a normal conversation?
65dB
Over how many decibels can you start to get hearing loss?
85dB
Frequency
the number of cycles per second of vibration, measured in Hertz (Hz)
it is perceived as pitch
What is the range of human hearing in Hertz?
20-20,000Hz depending on age
Sound is _______ into neural activity known as ______
transduced
action potentials
parts of the external ear
pinna and ear canal
pinna
collects sound waves and pushes them into the ear canal
ear canal
auditory canal
What does the shape of the ear do?
it modifies the character of sound
helps to pin point where the sound is coming from
function of the external ear
funnel sound
function of the middle ear
concentrate sound energy
What are the 3 ossicles in the inner ear?
malleus, incus, stapes
What do the ossicles connect?
the tympanic membrane (eardrum) to the oval window
what happens when sound hits the tympanic membrane?
it wiggles back and forth, vibrating through the ossicles
what are the 2 muscles in the inner ear?
tensor tympani and stapedius
tensor tympani
attached to the malleus and tympanic membrane
stapedius
attached to the stapes
acoustic reflex
when activated, muscles stiffen and reduce the sound’s effects
- ONLY protects against chronic, sustained loud noises
- not gun shots, short loud noises
Why does sound not appear as loud anymore overtime?
the muscles tighten and hold the ossicles in place so you get less vibrations and sound pressure reaching the inner ear
what connects the ear with the rearmost part of the palate (nasal cavity and throat)?
eustachian tube
function of eustachian tube
equalizes pressure on both sides of the eardrum
When does the eustachian tube open?
when you swallow and with positive pressure (ears pop on an airplane)
yawning, chewing
What part of the ear is responsible for turning sound into neural activity (action potential)?
inner ear
cochlea
endolymph
fluid in ear
cochlea
coiled structure with 3 parallel canals , only in mammals
What are the 3 parallel canals of the cochlea?
scala vestibuli
scala media
scala tympani
scala vestibuli
vestibular canal
scala media
middle canal
has:
- organ of corti
organ of corti
receptor system that converts vibration into neural cavity
scala tympani
tympanic canal
Hair cells in the organ of corti
embedded in basilar membrane
What does a high frequency sound displace?
and example
the narrow base of the basilar membrane
ex: crying baby
What does a low frequency sound displace?
and example
the wider apex (at very middle of cochlea)
ex: stereo bass
cilia tips of hair cells are joined by…
tip links
describe the mechanically gated ion channels in hair cells and what does this remind you of from other chapters?
cilia movement produces tension of the link which opens an ion channel in the adjacent tip
- like touch receptors (mechanoreceptors)
do hair cells fire action potentials?
NO
- but they depolarize resulting in a receptor potential
In hair cells what are the 2 types of sensory cells?
inner hair cells (IHC)
outer hair cells (OHC)
What do IHC do?
signal transduction
- release glutamate into synapse with vestibulocochlear nerve (CN8)
What does OHC do?
amplify and refine cochlea to help discriminate frequencies
hyperpolarization causes…
lengthening
depolarization causes…
shortening
Auditory nerve fibers from IHCs terminate in the
cochlear nuclei (synapse 1)
Cochlear nuclei send information to the
superior olivary nuclei (synapse 2)
cochlear nuclei relay sound information to what sides of the body
contralateral and ipsilateral superior olivary nuclei
What are the 2 divisions of the superior olivary nuclei?
- lateral superior olive
2. Medial superior olive
What does the lateral superior olive process?
intensity differences (loud vs. quiet)
What does medial superior olive process?
latency differences , but encodes sound by relative activity of the right and left sides
“when is it coming, what did it say”
What cues signal sound location
binaural
what are the 2 types of binaural cues
- interaural intensity differences
2. interaural latency differences
Interaural intensity differences
difference in loudness at the 2 ears
interaural latency differences
difference between the 2 ears in the time of arrival of sounds
duplex theory
sound localization requires processing f both intensity and latency differences
How many synapses are in the auditory pathway
5
First synapse in the auditory pathway
auditory nerve fibers from IHCs terminate in the cochlear nuclei
Second synapse in auditory pathway
cochlear nuclei send info to the superior olivary nucleu
Third synapse in the auditory pathway
superior olivary nuclei pass this info from both ears to the inferior colliculi
inferior colliculi
primary auditory centers of the midbrain
Fourth synapse in the auditory pathway
outputs of the inferior colliculi go to the medial geniculate nuclei
5th synapse of auditory pathway
pathways from here extend to the auditory cortex via internal capsule
What do all levels of the auditory pathway have?
tonotopic organization
arranged in a map according to the frequencies to which they respond
tonotopic organization
Where does brain imaging show the main area of activation is?
primary auditory cortex (A1) on the superior temporal lobes
What are the 2 main streams of ho the auditory cortex analyzes complex sounds?
dorsal stream
ventral stream
Dorsal stream
where and function
parietal lobe
involved in spatial location (Where is sound coming from)
receives info from BOTH ears
Ventral stream
where and function
temporal lobe
what am i hearing
pitch and volume
receives info from ONE ear
portion of auditory cortex that first processes music, it is larger in musicians than regular people
Heschl’s gyrus
amusia
inability to discern tunes
“tone deaf”
all levels of auditory processing have…
tonotropic organization
How is tonotropic organization arranged
based on frequencies they respond to
Where is the primary auditory cortex (A1) located?
superior temporal lobe and within the lateral (sylvian fissure)
Pure tones mostly activate what lobe of the brain?
temporal lobe
What areas of the brain do human speech sounds activate
several subcortical regions
Speech sound information is relayed to…
Wernicke’s area
Where is Wernicke’s area?
left cerebral hemisphere (junction between temporal and parietal lobes)
What is Wernicke’s area involved in?
SPOKEN language comprehension
What happens if you get damage to Wernicke’s area?
Wernicke’s aphasia
- you will not be able to understand what people are saying
Why do songs get stuck in your head?
cortical volume of Heschl’s gyrus is smaller in people prone to these “earworms”
ALSO frontal lobe smaller in these people
hearing loss vs deafness
hearing loss: reduced capacity to interpret sound
deafness: profound inability to hear (can not hear at all)
what can cause hearing loss?
aging, physical trauma
3 main causes of hearing loss and deafness
types of deafness
conduction deafness
sensorineural deafness
central deafness
disorders to the outer or middle ear that prevent sounds from reaching the cochlea
- not getting to hair cells of cochlea
- ossicle damage, ruptured ear drum, physical blockage
conduction deafness
deafness originates from cochlear or auditory nerve lesions
- damaged hair cells due to chronic loud noise
sensorineural deafness
deafness caused by brain lesions such as strokes
- cochlea is still intact
- damage to temporal lobe (brain injury), not reaching the primary auditory cortex (A1)
central deafness
3 ways to restore hearing defecits
hearing aids
teflon prosthetics
cochlear implants
use electronic amplification to deliver louder sounds to the impaired (but still functional) auditory system
hearing aids
what can fused ossicles be replaced with
- fused so they cannot vibrate in response to noise
teflon prosthetics
used to treat deafness due to hair cell loss
- electrical currents stimulate auditory nerve
cochlear implants
Functions of vestibular system
detects position and movement of the head
- helps maintain posture and balance
- lets you know if moving up/down, forward/backwards
- leads to motion sickness
what can people who get motion sickness blame?
faulty vestibular system
Where is the vestibula labyrinth located?
in inner ear next to cochlea
semicircular canals
3 fluid-filled tubes in different planes detect rotation
- nodding up and down
- tilting left and right
- shaking side to side
otolith organs
fluid-filled sacs that respond to movement
forward/backwards
Movement of head pushes _____ through canals to the ______
endolymph
ampulla
The ampulla has hair cells that are surrounded by….
gelatinous cupula coating
What happens when endolymph moves?
it bends/distorts the cupula opening K+ ion channels
depolarization opens Ca2+ channels and glutamate is released into synapse with the vestibulocochlear nerve
what cranial nerve is the vestibulocochlear nerve?
CN8
Otolith organs respond to movement
what is responsible for horizontal movement?
utricle
otolith organs respond to movement
what is responsible for vertical movement?
saccule
otolith organs have hair cells embedded in the macula covered in a gelatinous mass with _____ on top
otoconia
otoconia
tiny calcium carbonate crystals
What happens when you get the added weight of the otoconia?
It drags the hair cells when the head changes position, opening the K+ channels depolarizing leading to Ca2+ influx and glutamate release into vestibulocochlear nerve
What is Vertigo caused by?
when otoconia breaks off and migrates into the semicircular canals
- bumping crystals when moving tells canals head is moving even when it is not moving, get uncontrolled extra movement as if rotating when not
- get dizziness
What neurotransmitter do hair cells release into the synapse with the vestibulocochlear nerve
glutamate
Where are vestibulocochlear nerve cell bodies located
outside CNS in vestibular ganglion
Axons enter the brainstem and synapse on how many vestibular nuclei?
4
What brain regions do the axons of the vestibular nuclei cell bodies extend to?
brainstem (spinal cord, cerebellum, midbrain )
cerebellum
balance and gait control
midbrain (tectum)
eye movement
spinal cord
postural/balance movements
How do you get motion sickness?
contradicting inputs from the vestibular system and sensory inputs to brain
Scenarios that lead to motion sickness (4)
- actual vs expected motion
- motion that is felt but not seen
- motion seen but not felt
- motion perceived by both systems but do not match perfectly
Role of area postrema in motion sickness?
brain believes youmust be hallucinating, triggers vomiting
- gets “this does not match” signal, ingested a toxin
