Auditory Nerve Flashcards
How many sections of the IAM is there? What are the sections? What is the mnemonic that helps remember which part section is above the other?
There are four sections: 7th nerve, 8th nerve, superior vestibular nucleus, and inferior vestibular nucleus. The mnemonic is 7 up and coke down.
What is the anatomical pathway that the auditory nerve fibers are attached to the hair cells?
The auditory nerve travels from the hair cells through the habenula perforate in the osseous spiral lamina to the IAM.
What is a ganglion?
A ganglion is a group of neuronal cell bodies located outside the central nervous system.
What is the auditory nerve innervation density as a function of frequency?
Base and apex: 400 dibers/mm (3-4 IHC)
1-2 kHz: 1400 fibers/mm (15/IHC)
How many auditory nerve fibers are there in a human?
There are 30,000 auditory nerve fibers in a human.
What percentage of AN fibers are type I?
90-95% of auditory nerve fibers are Type I.
What type of connections do type I AN fibers have? Type II?
Multiple Type I fibers innervate each inner hair cell and have a many-to-one connection. Unlike Type I fibers, a Type II fiber innervates multiple outer hair cells.
Which AN fibers surely encode sound?
Type I fibers surely encode sound.
Where do the afferent and efferent AN fibers connect to IHCs? OHCs?
Inner hair cells are contacted directly by afferents and indirectly by efferents. Outer hair cells are contacted directly by both afferents and efferents.
Describe the tonotopic organization of the auditory nerve.
Auditory nerve fibers are ordered low-to-high in radial fashion. High frequency fibers are on the outside, middle frequency fibers are on the next ring, and low frequency fibers are directly in the middle.`
What type of fibers do we know a lot about and why?
Most knowledge comes from type I fibers because type II fibers are difficult to find and record.
Most neurophysiological information about the auditory system is conducted in what kind of experiment? What is measured in these experiments?
Most neurophysiological information about the auditory system is conducted with single cell neurophysiology experiments. The experiments occur when a microelectrode is placed into a single neuron. Stimuli is presented to the animal’s ears and the frequency of the stimulus is played over a large range of levels. If the stimulus is the frequency and sensitivity that the neuron is tuned to, the action potential from the neuron can be measured.
How is a PSTH generated?
In a physiology experiment, a stimulus is presented and the action potentials from a single neuron is recorded. To generate a PSTH, the clock is restarted at the onset of each stimulus. The firing over the entire stimulus is observed.
How is a period histogram generated?
A stimulus is presented and the action potentials from a single neuron is recorded. To generate a period histogram, the clock is restarted for each period. This demonstrates the phase locking and how firing only occurs in the rarefaction phase.
How is an interspike interval histogram generated?
A stimulus is presented and the action potentials from a single neuron is recorded. To generate an interspike interval histogram, the clock is restarted after each spike. This helps show that spikes occur at integer multiples of the period, and observe phase locking.
Describe the main sections of a primary-like PSTH? Why is it called primary-like?
The main sections of a primary-like PSTH are the resting potential, the onset, the steady-state response, and the recovery period. During the resting potential, the neuron is not responding to a specific stimulus, but there is some spontaneous firing. During the onset, the neuron has been depolarized and the action potential is occurring due to the presentation of a stimulus. Then the neuron has a steady state response to that stimulus. Lastly, the neuron enters the recovery stage, which is when the neuron is hyperpolarized and is trying to return to its resting potential.
It is called primary-like because it is the first neural encoding of the sound, and there is no real transformation of the auditory stimulation.
How does a PSTH get converted to a tuning curve? Response area?
To convert a PSTH to a tuning curve, a section is examined from the Y axis. For example, look at the response of three different neurons at 20 spikes/sec. To convert a PSTH to a response area, a section is examined from the X axis. For example, look at the response of the three different neurons at 50 dB SPL.
