AnaPhy of the Auditory System Flashcards
Encases the ear
Temporal Bone
Most visible part of the ear
Composed primarily of cartilage
Pinna/Auricle
What gives pinna its unique shape and size?
Concavities
What are the functions of the pinna?
Sound collection (funneling sound in)
Sound localization (ability to locate where sound is coming from)
Sounds arrive earlier in ear closest to sound source
Interaural timing difference
Difference in sound level due to head shadow effect and distance
Interaural level differences
Unique size and shape of pinna helps us determine where along vertical plane sound is coming from
Pinna effect
S-shaped canal; Access route to tympanic membrane
External Auditory Canal / External auditory meatus
What are the functions of the EAC?
For sound transmission
For sound resonation - amplification
Underlies the self-cleaning mechanism of the ear canal and removal of wax
Epithelial migration
Inflammation of outer ear
Otitis externa
Pushed earwax further into the ear
Impacted cerumen
Canal bends
EAC is short, straight and directed upwards
<3 years old
In children >3 years old, EAC is
S-shaped, long, directed downwards
To fully inspect the ears, we need to straighten the ear canals first then …
pull pinna down and back for <3 years old
pull pinna up and back for >3 years old
Pinna missing completely
Anotia
Pinna is small and not formed properly
Microtia
EAC missing completely
Atresia
EAC small/narrow
Stenosis
Grade at which the upper ear is severely deficient + the ear canal may be present or absent
Grade 2
Grade at which the ear is smaller but still looks like an ear
Grade 1
Grade at which the ear canal is absent
Grade 3
Grade at which there’s Anotia and Atresia
Grade 4
Elastic, thin, and cone shaped structure that is flexible and tough
Tympanic Membrane
Functions of the tympanic membrane
Protection
Sound Transmission
Only part of the tympanic membrane that is involved in transmission of acoustic energy from outer ear to middle ear; Larger, stiffer portion
Pars Tensa
Lax part of the Tympanic Membrane
Pars Flaccida
Middle ear inflammation
Common in children between 6-11 months
Otitis Media
Complication of Chronic Otitis Media
Build up of fluid in the middle ear space → pressure → TM bursts
Hearing loss of 0-40dB
Perforation
Smallest bones in the body that conducts sound from middle to inner ear
Ossicles
3 bones in the ossicular chain
malleus, incus, stapes
Where is the malleus attached to the TM?
Manubrium
Where is the stapes attached to the oval window?
via its foot plate
Bilateral reflex that protects against loud sounds
Acoustic reflex
Main muscle for Acoustic reflex
Stapedius
other muscle involved in the Acoustic reflex
Tensor tympani
Time delay of ____ is present for acoustic reflex and this presents a problem for sudden loud sounds
200 ms
Connects middle ear to the nasopharynx
Eustachian Tube
Function of the Eustachian Tube
Maintain air pressure within middle ear
Opens the Eustachian Tube during swallowing and yawning
Tensor Veli Palatini (CN 5, Trigeminal)
In infants and small children, eustachian tube is narrower, shorter and more horizontal
TRUE OR FALSE?
TRUE
Allows a sound wave travelling in air (in the outer ear and middle ear) to become a sound wave travelling in fluid (in the inner ear)
Middle Ear Transformation System
METS: High surface of TM → push small surface of oval window (caused by the pushing of the stapes footplate)
Gain Approx. : 25 dB
Areal ratio
METS: TM parts do not move in unison with one another → generates additional force
Gain Approx. : 6 dB
TM buckling effect
METS: Stapes → oval window → (upper chamber) scala vestibuli → apex → (lower chamber) scala tympani → round window will move forward and back → generates additional energy pabalik sa taas
Gain Approx. : 4 dB
Window phase differential
Innervation of the Conductive Pathway
CN 5 (Trigeminal)
CN 7 (Facial)
CN 9 (Glossopharyngeal)
CN 10 (Vagus)
2 Labyrinths on the Inner Ear:
___ - contains perilymph → encases the:
Membranous - contains ___
Bony, endolymph
Resembles a snail shell; a coiled structure
Cochlea
3 SCALA of the Cochlea
Scala vestibuli, scala media, and scala tympani
2 MEMBRANES of the Cochlea
Reissner’s membrane and basilar membrane
Contains several thousand hair cells/cilia that respond to vibrations of basilar membrane
Organ of Corti
2 Major Structures of the Organ of Corti
Hair Cells (Inner & Outer)
Basilar Membrane
Main structure that supports the traveling wave, responsible for the frequency tuning/ tonotopicity of the cochlea
Basilar Membrane
Base of the BM is narrow and stiff; responsible for
High Frequency
Apex of the BM is wider and more flaccid; responsible for
Low Frequency
Vibration of the basilar membrane gets picked up by hair cells
Transduction of Sound
Transduction of Sound up to the Central Pathway.
Explain.
Stapes → oval window → scala vestibuli → apex → scala tympani → move basilar membrane in scala media → vibration of the BM gets picked up by the hair cells → OHC comes in contact with the TM (jump and twitch) → motion of the TM is influenced (shearing motion)→ comes in contact with the IHC → stereocilia (hair-like structures on the IHC) bends → tip links (mechanically gated channels between the stereocilia where calcium and potassium enters) opens → triggers an electrical response (inflow of calcium and potassium inside the hair cell) → depolarization of the HC → release of neurotransmitter → can communicate with the auditory nerve → exits at the IAC → Fibers now terminate at the cochlear nucleus → synapse with neurons that ascend to the inferior colliculus which further extend to the medial geniculate body of the thalamus → neurons project to the auditory cortex (main area for auditory processing
Cochlear amplifier; jump and “twitch” to increase vibration along basilar membrane
Outer Hair Cells
True sensory neurons
Inner Hair Cells
Coding for Frequency: _____
Via the basilar membrane
Base (narrow and stiff): high freq.
Apex (wider and more lax): low freq.
Traveling Wave
Coding for Intensity: ______
Number of neurons firing (recruitment)
↑ recruitment = ↑ intensity
Rate of neural activity
CN 8
VESTIBULOCOCHLEAR NERVE
Hair cell receptors synapse with the ____ branch of CN 8
Cochlear branch
Vestibular branch
- Innervates the vestibular apparatus include the ___ of your inner ear
Semicircular canals
VCN exits through the ____
Internal auditory canal
