What makes the neurons of the auditory nerve with such high-speed? So the most labile are the fibers of the auditory nerve, in which the frequency of the generation of PD reaches 1000 Hz, while for skeletal muscles, it corresponds to 200 pulp / s, for smooth - 10-20 imp / s. Motor nervous ending can be transferred to the skeletal muscle and at all no more than 100-150 excitations in 1 s
High Speed vs High Frequency
For starters, what you are describing is a high frequency signal, not necessarily a high speed signal. High speed signals are caused by myelination (a sheath of fat deposits that encases neuron fibers), and by minimizing the number of actual dendrite/Axon junctions you need to pass through to get from point A to point B. In this respect, the nerves responsible for muscle control tend to be very long and have similar myelination to the cells in your ear; so, muscle control neurons would if anything transfer a signal faster than the more densely packed neurons in your ear.
Now to Answer the actual question: Why the Higher Frequency?
No one nerve in your ear actually needs to transmit a signal at a higher frequency than those nerves used by muscles. Instead you have a number of different nerves detecting for different audio frequencies, and your brain then receives a combination of signals that tell it that various Audio Frequencies are being detected 1. Each of the hairs in your inner ear tapers from the base to the apex such that the apex begins being stimulated by low frequencies, but the base only begins being stimulated by higher frequencies 2.
Each auditory nerve fiber is actually a cluster of nerves that work together at different frequencies to create a more complex signal. This results in a number of parallel signals that is interpreted as a complex (high frequency) signal.
Here is a simple diagram showing how low frequency signals can merge to make a higher apparent frequency.
Some animals can respond to sound in the microsecond range. They think that it's by using big groups of neurons working at the same time. Indeed, 1 cubic millimetre can contain 50,000 neurons / many receptors.
Echolocating bats are powerful models for investigating the underlying mechanisms of auditory temporal processing, as they show microsecond precision in discriminating the timing of acoustic events. However, the neural basis for microsecond auditory discrimination in bats has eluded researchers for decades. Combining extracellular recordings in the midbrain inferior colliculus (IC) and mathematical modeling, we show that microsecond precision in registering stimulus events emerges from synchronous neural firing, revealed through low-latency variability of stimulus-evoked extracellular field potentials (EFPs, 200–600 Hz). The temporal precision of the EFP increases with the number of neurons firing in synchrony. Moreover, there is a functional relationship between the temporal precision of the EFP and the spectrotemporal features of the echolocation calls. In addition, EFP can measure the time difference of simulated echolocation call–echo pairs with microsecond precision. We propose that synchronous firing of populations of neurons operates in diverse species to support temporal analysis for auditory localization and complex sound processing.
If you search for "auditory microsecond" that's the measure in which the science is studied, so you will find lots of results there.