What is the function of the auditory nerve?

The vestibulocochlear nerve constitutes the eighth cranial nerve pair and its function is essential for our survival, since it is thanks to it that we can hear and maintain our balance.

The way it sends information to the brain is somewhat complex, involving multiple pathways and activating several specific regions and types of neurons. Let’s take a closer look at the importance of this nerve.

In this article we are going to answer the question ‘’What is the function of the auditory nerve?’’ We will explain what the auditory nerve is, what its parts are and its functions.

What is the function of the auditory nerve?

The auditory nerve, also known as the vestibulocochlear nerve or the statoacoustic nerve, is responsible for auditory function and balance.

The human skull has twelve pairs of nerves connected to the brain. One of them, responsible for balance and hearing, is the auditory nerve, also called the vestibulocochlear nerve or the statoacoustic nerve. Its role is key to communicate, as it is responsible for processing the auditory impulses from the outer ear.

For this reason, when the auditory nerve is damaged and does not function properly, hearing loss always occurs. In this post we explain in detail what the auditory nerve is.

The auditory nerve is made up of two nerves of its own: the cochlear nerve, which carries information about sound, and the vestibular nerve, which carries information about balance. When the first fails, our hearing suffers. When the second is not working well, the consequence is dizziness.

Vestibulocochlear nerve, what is it?

The vestibulocochlear nerve (scientific name: nervus vestibulocochlearis) is the eighth cranial nerve (CN VIII), which is divided into two parts, the vestibular and the cochlear, both divisions being in charge of sensory function.

This nerve carries somatic afferent fibers from structures in the inner ear. While the cochlear part of the nerve is responsible for the sense of hearing, the vestibular part is responsible for aspects related to balance.

The vestibulocochlear nerve is responsible for sending information from the cochlea and vestibule to the brain, stimuli which will be interpreted in the form of sound and balance.

When a sound reaches the ear, the sound waves impinge on the internal structures of the ear causing them to vibrate. The cochlea transforms these vibrations into electrical impulses, which travel through a series of structures that lead to the auditory cortex of the brain.

In relation to balance, when we move our head the vestibule detects these movements and sends signals to the brain to indicate in what position we are or if we have momentarily lost our balance.

Within this structure we have a liquid that, when moving, activates cells, called hair cells or hair cells of the ear, which act as sensors. These cells send the signal to the brain, an organ that will activate the muscles necessary to correct position and maintain balance.

The auditory nerve and its functions

It is the eighth of the twelve cranial nerves and is responsible for balance and auditory function. The auditory nerve, also known as the vestibulocochlear nerve or the statoacoustic nerve, is responsible for auditory function and balance.

It is made up of two other nerves: the cochlear, which carries information about sound, and the vestibular, which does the same with information about balance. The origin of the auditory nerve is in the peripheral ganglia.

For its part, the cochlear nerve begins in the Corti ganglion and the vestibular nerve in Scarpa’s. The degree of greater or lesser balance is assessed based on the stability of the body that connects the ear with the brain stem.

Nerve impulses are transmitted from the hair cells, located in the inner ear, to the brain, where sounds are given meaning, that is, where auditory perception takes place.

When these cells move, they send electrical signals to the auditory nerve, which is where the sound information received by the outer ear is processed, so they are essential for us to hear.

Parts of this nerve

Below we will take a closer look at both sections:

1. Cochlear nerve

The cochlear nerve (scientific name: nervus cochlearis) is one of the two divisions of the vestibulocochlear nerve, responsible for hearing.

At the beginning of this section, it is found in the sensory receptors of the organ of Corti, travelling through the inner ear until it reaches the brain, where the auditory stimulus is processed.

Auditory information first passes through the thalamus and subsequently reaches the auditory cortex of the temporal lobe.

The cells responsible for receiving the auditory stimulus are hair cells that are found in the organ of Corti, which is located in the cochlea.

The information is sent to pseudounipolar neurons that are located in the spiral ganglion, located in the center of the cochlea. The axons of these pseudounipolar neurons are what make up the cochlear nerve itself.

After leaving the cochlea, the nerve enters the internal meatus where it joins the vestibular nerve, forming the vestibulocochlear nerve itself.

Both sections of the entire nerve travel to the posterior cranial fossa, entering the brain through the cerebellopontine angle, along with the facial nerve (CN VII).

In the brainstem bridge, the cochlear nerve fibers synapse with the posterior and anterior cochlear nuclei. The axons of the anterior nucleus form the trapezoid body.

Many of these fibers decay and end up in the upper olive complex. The axons of the neurons that arrive here, together with those of the posterior cochlear nucleus, form the lateral lemniscus, which travels until it reaches the inferior colliculus and the medial geniculate bodies.

Axons from the medial geniculate nucleus form the acoustic radiation of the brain, which passes through the internal capsule and ends in the superior temporal gyrus and transverse temporal gyrus (Brodmann areas 41 and 42). Here they synapse with cortical neurons.

2. Vestibular nerve

The vestibular nerve (nervus vestibularis) is the other division of the vestibulocochlear nerve. It receives the stimulation that the sensory receptors located in the membrane of the auditory labyrinth capture.

The vestibular nerve is responsible for the sense of balance, spatial orientation, and motor skills.

Most of the fibers of this nerve go to the brain, in the vestibular nuclei, but some of them go directly to the reticular nuclei without the need to make synapses along the way, and also end in the cerebellar nuclei.

The vestibular nerve arises from the receptors of the macules of the inner ear, specifically the utricle and the saccule, in addition to the receptors of the semicircular canals of the membranous labyrinth.

The receptors receive primary stimuli, and the neurons in the vestibular ganglion transmit the information from the receptors via their dendrites.

Axons that arise from neurons in the vestibular ganglion form the vestibular nerve, which joins its partner, the cochlear nerve, at the internal meatus of the ear, forming the vestibulocochlear nerve.

Fibers from the vestibular nerve reach the vestibular area in the brain, where it synapses with the vestibular nuclei. The axons of the neurons in these nuclei travel in several directions:

• Motor neurons of the anterior horn of the cord, via the vestibulospinal tract.
• Lower olive nucleus, via the vestibule-olive tract.
• Cerebellum, via the vestibulocerebellar tract.
• Cerebral cortex, via the ventral posterolateral nucleus of the thalamus.

Vestibulocochlear nerve injuries

Damage to this nerve can involve impairment of the sense of hearing and balance, manifested mainly in the form of hearing loss, dizziness, false sense of movement and loss of balance. When this nerve is affected, it is usually due to tumors, such as acoustic neuromas, which interfere with its function.

To assess damage to this nerve, fingers are placed in both ears and clicked, asking the patient if they hear the sounds bilaterally and if they are even in intensity.

It should be said that it is not always easy to detect diseases that can affect the vestibulocochlear nerve, although symptoms such as those mentioned above will appear, especially those involving loss of hearing and the ability to balance.

Hearing loss is usually a symptom associated with age, although being exposed to high intensity noise or having consumed drugs whose side effect may be deafness are also potential causes of nerve involvement.

If the fibers that make up the cochlear nerve are destroyed, the person begins to have difficulty understanding what he hears.

This difficulty increases when you are in very noisy environments, in conversations where more than two people are speaking at the same time, and if there is background noise.

Another symptom that indicates that the vestibular nerve is affected is the appearance of tinnitus, which is the subjective perception of sounds that do not really exist.

It is believed that the appearance of this phenomenon is due to the fact that the nerve is damaged and sends involuntary signals to the brain, an organ which interprets them as sounds that are actually invented.

Although the intensity of tinnitus varies from person to person, they can greatly affect the quality of life of those who suffer from it, especially if this phenomenon appears in the company of hearing loss. As a result, people with tinnitus can become depressed, irritable, and have trouble falling asleep.

In the event that tinnitus is due to injuries produced in the auditory nerve, it is very difficult to eliminate them completely, since it is necessary to repair the damaged cells in the nervous tract and this implies a very delicate surgical intervention.

One of the best options to deal with them, in addition to the surgical route, is to teach the patient to live with them.

It is for this reason that, taking all this into account, it is necessary to highlight the importance of prevention and good hearing hygiene.

To avoid having such annoying phenomena as tinnitus or different degrees of acquired deafness, it is advisable to avoid environments with high-intensity sounds, in addition to taking preventive measures when going to places with concerts and discos, such as not getting too close to the speakers.

If working in a noisy environment, such as a construction site where there are drills, protective headphones should be worn.

FAQS: What is the function of the auditory nerve?

What is the function of the auditory system?

The function of our auditory system is, essentially, to transform the pressure variations caused by the propagation of sound waves in the air into electrical impulses (potential variations), information that the acoustic nerves transmit to our brain for the assignment of meanings.

What do you mean by auditory nerve?

The auditory nerve, also known as the vestibulocochlear nerve or the statoacoustic nerve, is responsible for auditory function and balance.

What does damage to the auditory nerve do?

Hearing loss and balance problems can occur when critical parts of the ear, such as the eardrum, ear canal, ossicles, cochlea, or vestibular nerve are damaged.

What nerve is the auditory nerve?

The eighth. The auditory nerve, also known as the vestibulocochlear nerve or the statoacoustic nerve, is responsible for auditory function and balance.

Why is the auditory system important?

The sense of hearing helps us perceive sounds, their volume, pitch, timbre, and the direction from which they come. It also helps us to listen to the voice, music and most importantly to interact with different people through speech.

In this article we answered the question ‘’What is the function of the auditory nerve?’’ We explained what the auditory nerve is, what its parts are and its functions.

If you have any questions or comments please let us know!

References

Knipper M, Van Dijk P, Nunes I, Rüttiger L, Zimmermann U (2013). Advances in the neurobiology of hearing disorders: recent developments regarding the basis of tinnitus and hyperacusis. Prog Neurobiol. 111:17-33. doi: 10.1016/j.pneurobio.2013.08.002.

Hickox AE, Liberman MC (2014). Is noise-induced cochlear neuropathy key to the generation of hyperacusis or tinnitus? J Neurophysiol. ;111(3):552-64. doi: 10.1152/jn.00184.2013.