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Auditory Nerve
S&H A&P PowerPoint 6
| Question | Answer |
|---|---|
| Describe type II fibers within the cochlear nerve | Unmyelinated, too small to be studied, 5% of cochlear nerve. Spiral and make connection with three rows of outer hair cells. |
| Describe type I fibers within the cochlear nerve | Black, fatty coat of myelin wraps the nerve of each fiber, 95% of cochlear nerve. Each contacts ONE inner hair cell. |
| Type I and type II fibers are both | afferant, and both conduct information from the cochlea to the central nervous system |
| What happens in the absence of sound? | Auditory nerve fibers fire action potentials randomly--spontaneous discharge of glutamate from IHC (spontaneous activity) |
| What are the two mechanisms of frequency coding? | Tonotopy and phase-locking |
| Phase-locking | action potential is in phase at the same moment as the peak of condensation--therefore brain knows frequency of action potential by counting wavelengths. Reliable up to 4kHz |
| What are the two mechanisms of intensity level coding? | Firing rate and spread of excitation |
| Firing rate | the rate at which action potential is fired according to the frequency |
| Spread of excitation | The amount of action potential fired at different points along the basilar membrane |