The Ear & Taste Flashcards
3 Structural divisions of the ear
Outer ear Middle Ear Inner Ear
Outer Ear Does
Directs the sound wave into the auditory canal
Middle Ear
- Is air filled
- Contains the tympanic membrane, auditory ossicles.
- Sound waves cause the tympanic membrane to vibrate. In turn, the ossicles vibrate, pushing the stapes into the oval window and displacing fluid in the inner ear
Inner Ear
- Is FLUID filled 2. Contains Bony labyrinth (semicircular canals, cochlea, and vestibule)
Organ of Corti
- Located on basilar membrane
- Contains the receptor cells (inner/outer hair cells) for auditory stimuli. cilia protrude from the hair cells and are embedded in the tectorial membrane.
- Spiral ganglion contains the cell bodies of auditory nerve (CN VIII vestibulochoclear )
- Sound waves cause vibration of organ of Corti, causing bending of hair cells against the tectorial membrane.
- Fibers ascend to auditory cortex (41)
Hair Cells bending
bending as a result of hair cells on tectorial membrane In one direction –> Depolarization In the other direction –> Hyperpolarization This changing potential of the hair cells causes intermittent firing of COCHLEAR NERVES
Auditory Cortex location
area 41
Traveling waves….
along BASILAR MEMBRANE for high, medium, and low frequency sounds
High Frequency Sounds best respond where?
Base of basilar membrane (close to oval window)
Low Frequency Sounds best respond where?
APEX of basilar membrane
result of an ear infection
Likely loss of some high frequency hearing; selective deafness. middle ear damage
Auditory Pathway
- Both start in Medulla
1) Transcends the Cochlear Nuclei via CN VIII via the DORSAL ACOUSTIC STRIA - Crosses the PONS - Ascends to the Primary Auditory Cortex (area 41,42)
2) Anteriolateral path ascends through: -trapezoid body -Intermediate acoustic site -Superior Olivary Nucleus Nucleus of the lateral Lemniscus -Inferior colliculus -Medial geniculate nucleus -Ends in Primary Auditory Cortex (area 41,42)
CN VIII
Vestibulochoclear
Conductive deafness
defects in external or middle ear
-Foreign body, ear wax, destruction of auditory ossicals,
Bone Conductance > Air Conductance
air to bone gap should be >10
Nerve Deafness
Defects in the inner ear or CN VIII -Both bone and air conductance are reduced * Adverse effect of aminoglycosides
Adverse Effect of Aminoglycosides
Nerve Deafness
Audiogram deafness
>10 Dec = conduction deafness <10 Dec = nerve deafness
Which form of conduction is better in those with Middle ear sclerosis related deafness?
Bone Conduction
Where is there a significant INCREASE of pressure during administration of N2O?
Middle Ear
Use of N2O with middle ear diseases (otitis media, sinusitis) may result in:
Hearing loss or tympanic membrane rupture
N2O is contraindicated in
Tympanoplasty as the pressure difference bw middle and external ear can jeopardize the success of operation
Most sensitive taste bud
Sweet
Fungiform papillae
Sweet and Salty tastebuds
Foliate Papillae
Sour tastebuds
Circumvallate Papillae
Bitter tastebuds
Two Nerves of Life
- Facial (CN VII) - Salt & Sweet 2. Glossopharyngeal (IX) - Sour & Bitter
Taste Pathway Innervation
Anterior 2/3: CN VII Facial –> Chorda tympani (branch of cn 7) Posterior 1/3: CN IX Glossopharyngeal Back of Throat CN X Vagus – GAG reflex
Taste pathway
Medulla -> solitary tract –> solitary nucleus –> Thalamus –> Taste Cortex
Structures of Bony labyrinth
semicircular canals, cochlea, and vestibule
auditory ossicles
Malleus, incus and stapes Amplify sound
Stapes inserts into _____
the Oval Window a membrane bw the middle ear and inner ear.
Structure of the Cochlea
Three tubular canals: Scala Vestibuli (perilymph / ^ Na) Scala Tympani (perilymph / ^ Na) Scala Media (endolymph/ ^K)
