OHC/IHC Anatomy Physiology Flashcards
Base of OHC
Covering of OHC
Phalangal processes
Recticular Lamina
Distribution of afferent nerves
Many afferent nerves connected to one IHC. One afferent nerve connected to many OHC.
The volley principle
Limitations for both frequency and intensity of IHC can be overcome by multiple neurons firing. Combining and coordinating their actions like a team.
When does the nerve fire
Basilar membrane moves up and down to produce a transverse wave. Nerve is going to fire when it is depolarized.
Resting potentials of IHC and OHC
IHC -40uV
OHC -70uV
Tip Links
Open ion channels in hair cell membranes. Channel opens when stereocilia are pushed away from the modiolus. Channel closes when stereocilia are pushed toward the modiolus. Stereocilia are pushed due to movement of the basilar membrane. When gate is open potassium flows into the channels starting the chemical transmission of sound.
Cochlear anatomy
A transverse wave travels along the Scala media on which the organ of corti is located. The stereocilia of the hair cells project through the reticular lamina. The tallest stereocilia of the OHC embed into the tectorial membrane and bend because of the shearing motion caused by the difference in length because the basilar membrane attaches to the bottom of the osseous spiral lamina.
Cochlear Physiology
Shearing motion allows the ion channels to open when stereocilia move away from the Modiolus, allowing the positive potassium ions from the endolymph to flow into the hair cells leading to depolarization.
The periodicity theory
Can not perceive high frequency information
Hair cell afferent innervation
OHC unmyelinated type 2
IHC myelinated type 1
Cochlear amplifier
OHC responsible for, has greater effect on low intensity sounds. By OHC electromotility can increase the displacement of the basilar membrane. This causes IHC to fire more. OHC expand and contract.
When IHCs depolarize in the afferent system, what do they release to the auditory nerve
Glutamate
Efferent: acetylcholine
Olivocochlear Fibers
Olivo- superior olivary complex
Cochlear- indicates the destination
Direction- SOC is above the cochlea. Going from higher to lower structures- efferent
Efferent Auditory Pathway
- Primary and secondary cortical regions
- Medial geniculate body
- Lateral lemniscus
- Olivocochlear bundle
- Cochlear nucleus
- Internal auditory meatus
- Cochlea (afferent IHC fibers for LOC, directly to OHC for MOC)
Effect of efferent system on cochlear amplifier
OHC activity is suppressed which decreases cochlear amplification, which decreases IHC activity which decreases the afferent signal.
MOC releases Ach, which travels across synaptic cleft and attaches to receptor protein on OHC.
Calcium enters OHC. Opens potassium channels so the potassium flows out of OHC, hyperpolarizing the OHC.
