19. Spiral organ of Corti. Auditory pathway. Neuroanatomy of hearing, understanding and control of speech. Flashcards
Where is organ of Cori?
Organ of Corti situated in the cochlea
What is the role of Organ of Corti?
as the receptor of hearing
What is the role of hair cells?
They are responsible for transformation of sound waves into neural impulses (mechanoelectric transduction).
Within the bony cochlea three membranous ducts can be distinguished twisting 2 ¾ times around the axis of cochlea
-> What are these 3 membranous ducts?
the scala vestibuli, the cochlear duct (scala media) and the scala tympani.
What is helicotrema?
Where the Scala vestibuli and scala tympani are continuous at the apex of the cochlea
Cochlear duct is considered as a closed or open tube?
Cochlear duct is considered as a closed tube.
The base of stapes inserts into ___ (related to bone)
the foramen ovale
The base of stapes inserts into the foramen ovale and contacts the fluid inside ___
the scala vestibuli
The base of stapes inserts into the foramen ovale and contacts the fluid inside the scala vestibuli, while scala tympani is closed by ___
the secondary tympanic membrane in foramen rotundum.
Scala vestibuli and tympani contain ____
perilymph
the cochlear duct is filled by __.
endolymph
Type of cells are Inner and outer hair cells
secondary sensory epithelial cells
(They do not have axons!)
Type of cells are Inner and outer hair cells
secondary sensory epithelial cells
(They do not have axons!)
- Inner and outer hair cells
-> Identify
What is the difference between inner and outer hair cells?
- Cilia of inner hair cells float freely under the tectorial membrane, while those of outer hair cells are anchored into the tectorial membrane.
- Inner hair cells (IHC) are the major sources (approx. 95%) of acoustic signals, the outer hair cells (OHC) act as pre-amplifiers either driven by the waves themselfs or by efferent fibres coming from the brainstem.
What is the difference between inner and outer hair cells?
- Cilia of inner hair cells float freely under the tectorial membrane, while those of outer hair cells are anchored into the tectorial membrane.
- Inner hair cells (IHC) are the major sources (approx. 95%) of acoustic signals, the outer hair cells (OHC) act as pre-amplifiers either driven by the waves themselfs or by efferent fibres coming from the brainstem.
Movement of the basilar membrane evokes whirlpools between ___ and ___
the inner hair cells and the tectorial membrane
Movement of the basilar membrane evokes whirlpools between the inner hair cells and the tectorial membrane.
-> What is the consequence?
Whirlpools bend the stereocilia of the inner hair cells, which results in depolarisation and transmitter release.
Movement of the basilar membrane also bends the stereocilia of the OHCs which respond with ___ (2 things)
rearrangement of their cytoskeleton and shortenning of their hight.
Movement of the basilar membrane also bends the stereocilia of the OHCs which respond with rearrangement of their cytoskeleton and shortening of their hight.
-> What is the consequence?
As a result of this, tectorial membrane is pulled toward the basillar membrane, and in a narrower gap the amplitude of whirlpools stimulating IHCs is getting increased.
Outer hair cells have a double function which is ___
(1) they automatically amplify low-level signals (touching their „hair” shortens them which increases the amplitude of waves stimulating IHCs);
(2) and (2) have a roboust efferent innervation from the brainstem which modifies the sensitivity of the organ of Corti in certain frequency ranges.
Sound waves reach perilymph through ___
the chain of ossicles
Sound waves reach perilymph through the chain of ossicles.
-> The wave migrates along ____
the basilar membrane.
Basilar membrane is narrow and tense at the base, but wider and loose at the apex
-> What is the consequence?
Due to this, the base is sensitive to high frequency sounds, while the apex detects low frequencies.
Where is the Spiral ganglion?
Spiral ganglion is found in the spiral canal of modiolus
Describe the structure of spiral ganglion (Where is it found? It is constituted by?)
Spiral ganglion is found in the spiral canal of modiolus and is constituted by bipolar neurons.
=> Their peripheral axons contact hair cells and central processes enter the brainstem.
4 nerves arising from vestibular n.
facial nerve
utriculoampullar n.
saccular n.
posterior ampullary n.
What constitute the cochlear nerve? (axons, cells)
Central axons of bipolar cells constitute the cochlear nerve
The path of cochlear nerve
enter the brainstem and terminete in the cochlear nuclei found in the lateral recess of rhomboid fossa
Typically all the cochlear afferents divide into two
-> Why?
to share the auditory input both with the dorsal and ventral cochlear nuclei.
List nuclei and complex involving in auditory pathway
Organ of Corti
-> Ventral and dorsal cochlear nuclei
-> Superior olivary nuclear complex
-> Lateral lemniscus and its nuclei
-> Inferior colliculus
-> Medial geniculate body
-> Auditory cortex
In the cochlear nuclei, ___ and ___ all the ascending fibres terminate and synapse onto the upcoming neurons of the auditory pathway.
inferior colliculus and medial geniculate body
What is Frequency analysis?
Frequency analysis is performed in both of the cochlear nuclei, then signals are transferred toward higher auditory centres via different pathways.
Describe The role of Superior olivary complex
Superior olivary complex is the first synaptic site which receives bilateral input.
-> Medial and latertal nuclei (MSO and LSO) compare timing and amplitude of signals arriving from the left and right sides, respectively.
-> All these help to localize the source of sounds.
The role of the nuclei of lateral lemniscus
The role of the nuclei of lateral lemniscus is not clear, but they are probably connected to the reticular formation.
The role of Inferior colliculi
Inferior colliculi integrate various aspects of acoustic inputs, e.g. source, intensity and frequency.
The role of medial geniculate bodies
Both the medial geniculate bodies (MGB) have bilateral input, but only project into the auditory cortex of their own side.
=> They are considered as relay nuclei toward the cortex, but their function is much more complex.
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
- Olivocochlear bundle:
Superior olivary nuclei of both sides give rise to fibres returning into ____of both sides.
the organs of Corti
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
- Olivocochlear bundle:
Superior olivary nuclei of both sides give rise to fibres returning into the organs of Corti of both sides.
These fibres mainly terminate on _____ and modulate sensitivity of the auditory receptors in certain ranges of frequencies. Improve signal/noise ratio and supress irrelevant backround acoustic signals.
outer hair cells
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
- Olivocochlear bundle:
Superior olivary nuclei of both sides give rise to fibres returning into the organs of Corti of both sides.
These fibres mainly terminate on outer hair cells and modulate sensitivity of _____ in certain ranges of frequencies. Improve signal/noise ratio and supress irrelevant backround acoustic signals
the auditory receptors
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
- Olivocochlear bundle:
Superior olivary nuclei of both sides give rise to fibres returning into the organs of Corti of both sides.
These fibres mainly terminate on outer hair cells and modulate sensitivity of the auditory receptors in certain ranges of frequencies.
=> Improve ___ and supress irrelevant backround acoustic signals
signal/noise ratio
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
-> Explain 2. Protective (stapedius and tensor tympani) brainstem reflexes
Hair cells are very sensitive to long-lasting high sound pressures. Stapedius and Tensor tympani muscles may reduce the intensity of soundwaves reaching the inner ear
-> These two muscles act against the mobility of the chain of auditory ossicles.
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
-> How do they involve in Control of head movements?
superior and inferior colliculi are interconnected: not only visual but also acoustic signal may coordinate head and eye movements via the tectospinal tract and the medial longitudinal fascicle
While the auditory information travels upward in the brainstem, ascending collaterals may serve several functions
-> Explain Acoustic startle reflex
lateral lemniscus nuclei interact with the brainstem reticular formation, via the „ascending reticular activating system” the whole brain is prepared for giving an adequate response, automatic movements are carried out, the activity of endcrine organs and the autonomic nervous systems is modulated (fight-or-flight reaction).
Name 2 Cortical fields on both sides
Primary auditory cortex (Br. 41):
termination site of specific auditory afferents
Secondary auditory cortex (Br. 42): association auditory area, recognizing what we hear, acoustic memory
Name 2 Cortical fields on both sides
Primary auditory cortex (Br. 41):
termination site of specific auditory afferents
Secondary auditory cortex (Br. 42): association auditory area, recognizing what we hear, acoustic memory
Cortical fields
-> The role of Primary auditory cortex (Br. 41)
termination site of specific auditory afferents
Cortical fields
-> The role of Secondary auditory cortex (Br. 41)
association auditory area, recognizing what we hear, acoustic memory
