Auditory System Flashcards
What cranial nerve is part of the auditory system?
CN VIII
CN VIII is SA or SE? What is it’s function?
SA, hearing and equilibrium
What happens with lesion of the vestibulocochlear nerve?
Ipsilateral deafness
Loss of equilibrium
Structures of the external ear
Auricle (pinna)
External acoustic meatus (external ear canal)
TM
Structures of the middle ear
Malleus
Incus
Stapes
What is the vestibule?
Inner ear bony structure encased by the temporal bone that is responsible for balance
The vestibular labyrinth of the internal ear contains the following structures
Vestibule and 3 semicircular canals
What does the vestibule contain?
Membranous utricle and saccule with macula as receptor organ
What do the semicircular canals contain?
Semicircular ducts with ampullae
What do the ampullae of semicircular ducts contain?
Crista ampullaris as receptor organ
What are the general functions of the vestibular system?
- Regulate body and limb posture through cerebellum and vestibulospinal tract
- Regulate eye movements to keep eyes fixed on object when head is in motion
What is the VOR reflex?
Vestibuloocular reflex
Regulates eye movements to keep eyes fixed on an object when head is in motion
What is the function of the utricle?
Monitor and activate linear acceleration of horizontal movements
Side to side, front to back
What is the function of the saccule?
Monitor and activate response to linear acceleration of vertical movements
Up and down
What is the function of the three semicircular ducts?
Monitor and activate angular acceleration of head in all planes
What are the three fluid-filled cavities (membranous cochlea) in the internal ear?
Scala vestibuli
Scala tympani
Scala media (cochlear duct)
Which membranous cochlea contains the organ of corti?
Scala media
What is the organ of corti?
Receptor organ of the auditory system
The cochlear duct is the structure where sound travels from base to apex of the cochlea. Where are the high frequencies located? Low frequencies?
High frequencies: base
Low frequencies: apex
Frequency of sound determines frequency of traveling wave in basilar membrane. Each traveling wave will maximally activate the basilar membrane a specific distance from base dependent on ____
Frequency
Hair cells are ___ cells that are housed in ____
Receptor
Organ of corti
Hair cells produce _____ transduction
Mechanoelectrical (convert movement into electrical signals)
What causes depolarization of hair cells?
Stereocilia deflected toward tallest stereocilium
Pulls and stretches tip links which causes the cells to be more active
What causes hyperpolarization of hair cells?
Stereocilia deflected towards shortest stereocilium
Presses tip links and makes them shorter which causes the cells to be less active
There is __ hair cell for ___ stereocilia
One hair cell for many stereocilia
Tip links ___ stereocilia
Connect
The displacement of stereocilia of hair cells towards tallest stereocilium leads to conversion of
Movement into electrical signals, causes depolarization of hair cells and bipolar neurons
The displacement of stereocilia of hair cells towards shortest stereocilium leads to
Hyperpolarization of hair cell and bipolar neurons
Overview of the auditory pathway
First order neurons: CN VIII, spiral ganglion
Second order neurons: Cochlear nuclei, pontine structures
Inferior colliculus
MGN neurons of thalamus
Sublenticular limb of internal capsule
Auditory radiation
Primary auditory cortex
What part of the internal capsule is part of the auditory pathway?
Sublenticular limb: axons from MGN neurons of thalamus to primary auditory cortex
The primary auditory cortex is the ____(think structure)
Transverse temporal gyri of Heschl
Where does higher level processing of the auditory cortex occur?
Downstream of the primary auditory cortex
Blood supply of auditory system: the following structures are supplied by
1. Primary auditory cortex
2. Inferior colliculus and MGN
3. Pontine structures
4. Internal ear and cochlear nuclei
- MCA
- PCA
- Basilar artery
- AICA of basilar artery
What structure is responsible for sound localization?
Superior olivary nuclei
The superior olivary nuclei are responsible for
Receiving bilateral auditory input
Important for localizing sounds in space
What is air conduction?
Sound waves are sent through the external ear via air, vibrate TM, oscillate middle ear bones, activate inner ear neurons
What is bone conduction?
Sound vibrations conducted to internal ear through temporal bone
Bypass external and middle ear
What is nerve (sensorineural) deafness?
Total ipsilateral deafness
Neural pathway disrupted at or before cochlear nuclei
What causes nerve (sensorineural deafness)?
Damage to hair cells or organ of corti
Damage to spiral ganglion or CN VIII or cochlear nuclei
Inflammation/infection in cochlea
Are AC and BC affected by nerve deafness?
No
What is central deafness?
Virtually no loss of hearing
Difficulty in interpreting or localizing sounds
Neural pathway disrupted at after cochlear nuclei
Are AC and BC affected by central deafness?
No
What is conduction deafness?
Partial ipsilateral deafness with interruption of air conduction of sound waves
Neural pathway intact
Causes of conduction deafness?
Inflammation/infection of EAM
Cerumen buildup
TM trauma or inflammation
Otitis media
Middle ear bone damage
Otosclerosis
Are AC and BC affected by conduction deafness?
AC: diminished or eliminated
BC: unaffected
Why is there virtually no loss of hearing with damage to proximal to cochlear nuclei?
Bilateralism that occurs in several locations of the auditory pathway
Where does bilateralism occur in the auditory pathway?
Commissure of inferior colliculus
Commisssure of lateral lemniscus
Trapezoid body
