10. Auditory system Flashcards
Ear anatomy
Middle ear: 3 constituents
- Tympanic cavity (air-filled)
- 3 ossicles (Malleus, incus, stapes)
- Tympanic membrane (pars flaccida and pars tensa) - in contact with manibrium of malleus
Ear anatomy
Which elements separate the middle ear from
* External ear
* Inner ear
* Nasopharynx
- External ear: TYMPANIC MEMBRANE
- Inner ear: OVAL (vestibular) & ROUND (cochlear) windows
- Nasopharynx: communicate via AUDITORY TUBE
Ear anatomy
Princple of BENT LEVER of ossicles (slide 50)
- Malleus has a long arm attaching to TM
- Incus has a short arm attaching ot vestibular window
- This REDUCES the amplitude of sound waves at the vestibular window
Ear anatomy
2 muscles (reflexes) protecting ear agaist noise
- Tensor tempani muscle (attached to MALLEUS) - CN V
- Stapedium muscle (attached to STAPEDIUS) - CNVII
Ear anatomy
2 major components of the inner ear
Bony and membranous labyrinths
Ear anatomy
Difference between bony vs membranous labyrinths
Bony labyrinth
* In the petrous portion of temporal bone
* Filled with perilymph (~CSF, Na+ > K +)
* Semi-circular canals (anterior, posterior, lateral)
* Vestibule
* Cochlea
Membranous labyrinth
* Filled with endolymph (~serum, K + > Na +)
* Semi-circular ducts (rotation of the head)
* Utricule & saccule (linear acceleration) - in the vestible
* Cochlear duct (sounds)
Ear anatomy
Where is the organ of corti?
In the cochlear duct (endolymph)
Ear anatomy
3 divisions of the cochea
- COCHLEAR DUCT (endolymph)
- SCALA VESTIBULI (dorsally, faces vestibular window, periplymph)
- SCALA TYMPANI (ventrally, faces cochlear window, perilymph)
OTHER POINTS:
* SV and ST are connected at the HELICOTREMA (apex)
* CD separated from SV via VESTIBULAR MEMBRANE
* CD separated from ST via BASILAR MEMBRANE
* ST connects with subarachnoid space at COCHLEAR CANNICULUS
Where does the inner ear connect with subarachnoid space?
COCHLEAR CANNICULUS: connects the scala tympani with the subarachnoid space -> Otitis interna can lead to meningitis
Ear anatomy
What is the stria (area) vascularis?
- Produces endolymph
- Regulates [ion] in cochlear duct
- Maintains Endolymphatic potential of +80mV
Ear anatomy
3 components of the organ of corti
- BASILAR MEMBRANE- sonotopic organization (high f at the base (narrow and tought), low f at the apex (wide and floppy)
- TECTORIAL MEMBRANE - sits on hair cells
- HAIR CELLS (inner & outer) - have sterocilia with tip links, height increases towards outer border
- SUPPORTIVE CELLS
Ear anatomy
Mechanism of hair cells transduction in the organ of corti (also: summary of sound transduction BAER slide 11)
- Movement of basilar membrane
- Bending of stereocilia against the tectorial membrane -> Tip-links are stretched -> opening of K+ channels
- K+ influx -> hair cell depolarization
- Neurotransmitters released across synaptic cleft
- AP generated in the cochlear nerve
Ascending auditory pathway
Describe the steps of the ascending auditory pathway
- N1: Cochlear nerve (bipolar neurons; synapse with hair cells, reach spiral ganglion in bony cochlea, form cochlear nerve, enters internal acoustic meatus, to medulla)
- N2: Cochlear nuclei (DORSAL CN -> acoustic stria -> contrala lateral lemniscus; VENTRAL CN -> synapse with bilat dorsal nuclei of trapezoid body -> bilat lateral lemniscus)
- N3: Caudal colliculi (auditory reflex center)
- N4: MGN (thalamus)
- Auditory cortex (temporal lobe)
Ascending auditory pathway
Name the BAER waves
- I: cochlear nerve
- II: cochlear nuclei
- III: dorsal nucleus of trapezoid body
- IV: lateral lemniscus
- V: caudal colliculus
- VI: MGN
- VII: auditory cortex
Descending auditory pathways
Describe the steps of the descending auditory pathway (slide 63)
Reverse pathway:
* Auditory cortex
* MGN
* caudal colliculus
* lateral lemniscus
* dorsal nucleus of trapezoid body (DNTB)
* IPSI Inner hair cells + BILAT outer hair cells
