Vestibulocochlear nerve: what is it and what are its functions?

This cranial nerve is involved in the perception of sound and the sense of balance.

The vestibulocochlear nerve is the eighth cranial nerve pair and its function is essential for our survival. nerve and its function is fundamental to 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 regions and specific types of neurons. Let's take a deeper look at the importance of this nerve.

Vestibulocochlear nerve: what is it?

The vestibulocochlear nerve (scientific name: nervus vestibulocochlearis) is the eighth cranial nerve (NC VIII), which is divided into two parts, the vestibulocochlear nerve and the vestibulocochlear nerve. is divided into two parts, the vestibular and the cochlear.Both divisions are in charge of the sensory function. This nerve carries somatic afferent fibers from structures of 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 by the brain.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 strike 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 leading 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 which position we are to indicate in which position we are or if we have momentarily lost our balance. Inside this structure we have a liquid that, when moving, activates cells called ciliary or hair cells of the ear, which act as sensors. These cells send the signal to the brain, which activates the muscles necessary to correct the position and maintain balance.

Parts of this nerve

We will now take a more in-depth look at both sections:

1. Cochlear nerve

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

At the beginning of this section it is located at the sensory receptors of the organ of CortiThe vestibulocochlear nerve travels through the inner ear until it reaches the brain, where the auditory stimulus is processed.

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

The cells in charge of receiving the auditory stimulus are hair cells located in the organ of Corti, which is located in the cochlea.

The information is sent to pseudounipolar neurons located in the spiral ganglion, located in the center of the cochlea.located in the center of the cochlea. The axons of these pseudounipolar neurons form 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 pontocerebellar angle, along with the facial nerve (vestibulo-cochlear nerve).along with the facial nerve (NC VII).

At the brainstem bridge, cochlear nerve fibers synapse with the posterior and anterior cochlear nuclei. Axons from the anterior nucleus form the trapezoid body.

Many of these fibers decussate and go to the superior olivary complex.. The axons of the neurons arriving here, together with those from the posterior cochlear nucleus form the lateral lemniscus, which travels to 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 medial geniculate capsule.which passes through the internal capsule and terminates in the superior temporal gyrus and transverse temporal gyrus (Brodmann's 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 stimulation from sensory receptors located in the membrane of the auditory labyrinth.

The vestibular nerve is responsible for the sense of balancespatial orientation and motor skills.

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

The vestibular nerve arises from the receptors of the maculae of the inner ear, namely the utricle and the saccule, in addition to the receptors of the vestibular ducts of the cerebellar nuclei.The vestibular nerve arises from the receptors of the semicircular canals of the membranous labyrinth.

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

The axons that arise from neurons in the vestibular ganglion form the vestibular nerve, the vestibular nerve, the vestibular nerve, the vestibular nerve, and the vestibular nerve. the vestibular nerve, which joins its partner, the cochlear nerve, in the inner meatus of the ear.in the inner meatus of the ear, forming the vestibulocochlear nerve.

Vestibular nerve fibers reach the vestibular area in the brain, where they synapse with the vestibular nuclei. Axons of neurons from these nuclei travel in various directions:

• Motor neurons of the anterior horn of the medulla, via vestibulospinal tract.
• Inferior olivary nucleus, via vestibulo-olivary tract.
• Cerebellum, via vestibulocerebellar tract.
• Cerebral cortex, via ventral posterolateral nucleus of the thalamus.

Lesions in the vestibulocochlear nerve.

Damage to the vestibulocochlear nerve may involve impairment of hearing and balance.The main symptoms are hearing loss, vertigo, dizziness, dizziness, false sensation of movement and loss of balance. When this nerve is affected, it is usually due to tumors, such as acoustic neuromas, which hinder its functioning.

To evaluate damage to this nerve, fingers are placed in both ears and snapped.The patient should be asked if he/she hears sounds bilaterally and if they are even in intensity.

It should be said that it is not always easy to detect diseases that may affect the vestibulocochlear nerve, although symptoms such as those mentioned above will show up, especially those involving hearing loss and loss of balance. Hearing loss is usually a symptom associated with age, although being exposed to high intensity noise or having taken drugs whose side effect may be deafness are also potential causes of nerve involvement.

If the fibers that form the cochlear nerve are destroyed, the person begins to have difficulty understanding what he or she hears.. This difficulty is exacerbated in noisy environments, in conversations where more than two people are talking 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 occurrence of this phenomenon is due to the fact that the nerve is damaged and sends involuntary signals to the brain, which interprets them as sounds that are actually invented.

Although the intensity of tinnitus varies from person to person, it can have a great effect on the quality of life of the sufferer, especially if the phenomenon appears together with hearing loss. As a result, people with tinnitus may become depressed, irritable and have trouble sleeping.

If tinnitus is caused by damage to the auditory nerve, it is very difficult to completely eliminate it.The patient has to repair the damaged cells in the nervous tract and this involves a very delicate surgical intervention. One of the best options to deal with them, in addition to surgery, is to teach the patient to live with them.

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

To avoid annoying phenomena such as tinnitus or different degrees of acquired deafness, it is advisable to avoid environments with high intensity sounds, as well as to take preventive measures when going to places with concerts and discotheques, such as not getting too close to the loudspeakers. If working in a noisy environment, such as a construction site where there are drills, protective headphones should be used.

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.