Lecture 15: Special senses: hearing Flashcards
What is sound
Cyclical compression and rarefaction of air molecules causes a cyclical change in air pressure
Sound is characterized in the ___ and ___ domains
Spectral and temporal
What structures make up the outer ear
Pinna, ear canal, tympanic membrane
What structures make up the middle ear
Auditory ossicles- malleus, incus, stapes, tympanic bulla, eustacian tube
What structures make up the inner ear
Bony labyrinth- cochlea, utricle, semicircular canals, CN VIII
What is the purpose of the pinna
Funnel and conduct sound toward the meats and tympanic membrane
Besides hearing what is another function of the pinna/outer ear
Thermoregulation
Is the middle ear air or fluid filled
Air
What is the function of the eustachian tube
Maintain pressure equilibrium
What is the function of the ossicles
Optimal energy transfer
What is the function of the skeletal muscles attached to malleus (tensor tympani) and stapes (stapedius)
Reduce energy transfer when they contract, thus give protection from excessive noise
Is the inner ear fluid or air filled
Fluid
What function of the inner ear is the auditory portion
Cochlea
What two membranes make up the cochlea
- Basilar
- Reissner’s
What 3 chambers make up the inner ear
- Scalae
- Scala vestibuli
- Scala tympani
What fluid fills the scalae
Endolymph
The scalae is rich in what ion
K+
The Scala vestibuli and Scala tympani are filled with what fluid
Perilymph
What does the organ of corti contain
Contains the hair cells that are anchored to the basilar papilla
What is the gel-coated ridge that lies on the hair cells
Tectorial membrane
Hair cells synapse to sensory nerves from the cochlear nerve to…
CN VIII
What structure encodes for sound waves of different frequencies
Basilar membrane
The basilar membrane allows for ___ coding along the length of the membrane, which is known as ___
Spatial coding, tonotopic organization
What frequency is encoded closest to the stapes and oval window
High frequencies
What frequency is encoded farthest from the stapes and oval window
Low frequencies
Which membrane in the organ of corti is very stiff
Tectorial
Which membrane in the organ of corti is very flexible
Basilar
what membrane is displaced by traveling sound waves
Basilar membrane
What happens when the basilar membrane is displaced
Cilia tilt towards stereocilia, causing neurotransmitter release
How is information transduced in the ear
- Sound waves hit the tympanic membrane
- Vibrations are transferred to the oval window
- Oval window deformations creates pressure waves in the perilymph of the cochlea
- Pressure waves travel up the basilar membrane
- Hair cells tilt and depolarize
Describe the mechanical-electrical transduction
- Bent hairs open mechanically gated cation channels
- K+ enters the hair cell
- Hair cell depolarizes
- Voltage gated Ca2+ channels open
- NT- glutamate- released signaling terminals of the cochlear nerve
Mechanical energy is transduced to electrical energy in the form of ___
Action potential
How are quiet noises detected
- Pinna funnels into ear canal
- Meatus transmits sounds
- Middle ear ossicles amplify sound 2-3 times
- Cochlear amplifier
What two structures mainly amplify sounds
Ossicles and cochlear amplifiers
What hair cells amplify the signal
Outer hair cells
How do outer hair cells amplify signal
Change length in response to movements of basilar membrane and amplify signal, increase sensitivity of inner hair cells
Describe the pathway of the auditory nervous system
- Spiral ganglion synapses with hair cell
- Forms the cochlear nerve and joins with CN VIII
- Synapses in cochlear nuclei in medulla
- Travels and synapses in superior olivary complex (medulla-pons)
- Travels and synapses to inferior colliculus (mesencephalon)
- Travel and synapse in the medial geniculate nucleus
- Auditory cortex
What does the superior olivary complex do
Sound localization
What does the medial geniculate nucleus and inferior colliculus do
Specialized to detect certain frequency combinations and timing sounds
What does the auditory cortex do
Conscious perception of sound
How is sound localization achieved
Time differences and intensity differences in the olivary complex
What does the lateral superior olive do
Cells measure interaural intensity differences by integrating ipsilateral excitatory and contralateral inhibitory inputs
What is the medial superior olive
Cells measure interaurel time differences using excitatory inputs from both sides
What does wave I represent in the BAER test
Reflects cochlea, spiral ganglia and CN VIII
What does wave II represent in the BAER test
Reflects the cochlear nuclei
What does wave III represent in the BAER test
Reflects the superior olivary complex
What do waves IV and V in present in the BAER test
Reflect the lateral lemniscus and lemniscal nuclei and caudal colliculus
What does wave VI represent in the BAER test
Medial geniculate body
What does wave VII represent in the BAER test
Auditory radiations
which puppies can hear in both, one or none of its ears
Puppy 1: both ears
Puppy 2: right ear
Puppy 3: left ear
Puppy 4: neither
What is acquired deafness
Hearing loss due to an infection, injury, gradual or sudden hearing loss due to age, noise exposure or drugs
What do ototoxic drugs do
- Non-selective cation channels allow passage of drugs like aminoglycosides
- Upon entering hair cells, ototoxic drugs cause cell death, hearing loss
How do ototoxic drugs cause hearing loss
Target mitochondrial function
Where do aminoglycans target the basilar membrane and therefore what frequencies are affected
Affect the basal portion of the cochlear spiral and therefore affect high frequency sounds first
What type of hearing loss do aminoglycosides cause
Permanent
What type of hearing loss does cisplatin cause
Permanent
What type of hearing loss does furosemide cause
Temporary
What frequency range of hearing is lost with aminoglycosides
High frequencies with progression to low frequencies
What frequency range of hearing is lost with cisplatin
High frequencies with progression to low frequencies
What frequency range of hearing is lost with furosemide
Middle frequencies
What hair cells are lost with aminoglycosides
Beginning in the base and progressing towards the apex
What hair cells are lost with cisplatin
Beginning in the base and progressing toward the apex
What hair cells are lost with furosemide
None
What changes to the cochlear nerve occur with aminoglycosides
Nerve degeneration following hair cell loss
What changes to the cochlear nerve does cisplatin cause
Damage at the basal coil and decrease in function
What changes to the cochlear nerve does furosemide cause
Temporary impairment of function
What effect does aminoglycosides have on balance
Possibly severe
___coat color is linked to deafness
White
Deafness develops at 3-4 weeks due to loss of….
Melanocyte dependent blood supply to the cochlea