Auditory Nerve Physiology

Graded potential

amplitude increases in proportion to the amount of stimulation

examples: cochlear microphonic, summating potential

Action potential

All or none electrical discharge

firing

the discharge of a spike potential

firing/discharge rate

the number of action potentials discharged per second

Spontaneous rate

the rate at which a neuron fires on its own when there is no stimulation 

What information does the auditory nerve bundle encode?

Frequency and intensity

Must be able to preserve that information from the cochlea to the nerve as it goes to the higher nuclei

Frequency coding depends on what two things

Characteristic frequency

firing pattern

Characteristic frequency

The frequency of the lowest threshold/greatest firing rate

Tuning curve characteristics for HF and LF

LF broader, symmetric

HF narrower, asymmetric

Firing pattern

the manner in which spikes are elicited over time

Post-stimulus time histogram (PSTH)

Number of spikes that occurred during a period of time after an acoustic stimulus is applied

Can reveal firing patterns 

Spikes are phase-locked to cycles of the sinewave 

phase locking

the time locking of neural discharges to the acoustic waveform

Volley principle

Other nerve fibers are recruited into action when one nerve fiber reaches its maximum firing rate

Dynamic range of a neuron

The range of intensity over which the aud nerve fiber continues to respond with increasing magnitude

about 40 dB

Saturation

when you increase the stimuli but the response spikes do not increase

Spontaneous rates (low, med, high)

Low: 0-0.5 spikes/s

Med 0.5-18 spikes/s

High: >18 spikes/s

High spontaneous rate fibers characteristics

Larger in diameter

Usually towards the organ of Corti

low thresholds

Narrow dynamic range

Low spontaneous rate fibers characteristics

Smaller in diameter

usually towards the modiolus

high thresholds

wide dynamic range

How do you get a more broad dynamic range

Nerve fibers working together