Vestibulocochlear nerve: what is it and what functions it has

The vestibulocochlear nerve constitutes the eighth cranial pair nerves and its function is fundamental for our survival, because it is thanks to it that we can feel and maintain our balance.

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

    What is the vestibulocochlear nerve?

    The vestibulocochlear nerve (scientific name: nervus vestibulocochlearis) is the eighth cranial nerve (NC VIII), which it is divided into two parts, the vestibular and the cochlear, With the two divisions in charge of sensory function. This nerve carries the somatic afferent fibers of the 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 lobby to the brain, Whose stimuli will be interpreted as sound and balance.

    When sound reaches the ear, sound waves affect the internal structures of the ear and cause them to vibrate. The cochlea transforms these vibrations into electrical impulses, which pass through a series of structures that flow in the auditory cortex of the brain.

    With respect to balance, when we move our head in the hall, it detects these movements and sends signals to the brain to indicate what position we are in or if we have momentarily lost balance. In this structure, we have a fluid which, as it moves, activates cells, called ciliary or hairy cells in the ear, which act as sensors. These cells send the signal to the brain, an organ that will activate the muscles needed to correct posture and maintain balance.

      Parts of this nerve

      Below, we’ll take a closer look at both sections:

      1. Cochlear nerves

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

      At the start of this section, it is found in the sensory receptors of the organ Corti, Travel through the inner ear to the brain, where the auditory stimulus is processed.

      Auditory information first passes through the thalamus and then reaches the auditory cortex in the temporal lobe.

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

      The information is sent to pseudounipolar neurons located in the spiral ganglion, Located in the center of the cochlea. The axons of these pseudounipolar neurons are those that 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.

      The two sections of the complete nerve they move to the posterior cranial fossa, entering the brain through the pontocerebellar angle, With the facial nerve (NC VII).

      In the brainstem, cochlear nerve fibers synchronize with the posterior and anterior cochlear nuclei. Axons of the anterior nucleus form the trapezoidal body.

      Many of these fibers break down and end up in the upper complex of the olive.. The axons of the neurons that arrive there, along with those of the posterior cochlear nucleus, form the lateral lemniscus, which travels to the inferior and medial geniculate bodies of the colic.

      Axons of the medial geniculate nucleus form the acoustic radiation of the brain, Which crosses the internal capsule and ends in the superior temporal gyrus and the transverse temporal gyrus (Brodmann zones 41 and 42). Here they make synapses with cortical neurons.

      2. Vestibular nerves

      The vestibular nerve (vestibular nerve) is the other division of the vestibulocochlear nerve. It receives the stimulation picked up by the sensory receptors located on the membrane of the auditory labyrinth.

      The vestibular nerve he is responsible for the sense of balance, Spatial 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 make synapses along the way, and also end up in the nuclei. cerebellar.

      The vestibular nerve originates from the receptors of the inner ear macules, especially the utricle and the sacrum, In addition to the receptors of the semicircular canals of the membranous labyrinth.

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

      Axons that emerge from neurons as a vestibular ganglion the vestibular nerve, which joins its companion, the cochlear nerve, In the internal meatus of the ear, forming the vestibulocochlear nerve.

      Vestibular nerve fibers reach the vestibular area of ​​the brain, where they synapse with the vestibular nuclei. The axons of the neurons in these nuclei travel in several directions:

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

      Vestibulocochlear nerve injury

      Damage to this nerve can lead to impaired hearing and balance, Which mainly manifest as hearing loss, dizziness, lightheadedness, false sense of movement and loss of balance. The damage to this nerve is usually due to tumors, such as acoustic neuromas, which interfere with its function.

      To assess damage to this nerve, the fingers are placed on both ears and are caused to explode., Ask the patient if he hears the sounds bilaterally and if they are even in intensity.

      It should be noted that it is not always easy to detect diseases that may affect the vestibulocochlear nerve, although symptoms such as those mentioned above will be visible, especially those that involve hearing loss and the ability to the balance. Hearing loss is usually a symptom of aging, although being exposed to high intensity noise or using medication, the side effect can be deafness, are also potential causes of nerve damage.

      If the fibers that make up the cochlear nerve are destroyed, the person begins to have difficulty understanding how they are feeling. This difficulty goes further when you are in noisy environments, in conversations where there are more than two people talking at the same time and in case of background noise.

      Another of the symptoms that indicate that the vestibular nerve is affected is the onset of tinnitus, which is the subjective perception of sounds that are not really there. 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 actually made up sounds.

      Although the intensity of tinnitus varies from person to person, it can have a major impact on the quality of life of those who suffer from it, especially if it occurs 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 damage to the auditory nerve, it is very difficult to eliminate it completely.As it is necessary to repair damaged cells of the nervous system and this involves very delicate surgery. One of the best options to deal with them, besides the surgical route, is to teach the patient to live with them.

      It is for this reason that, in view of all this, it is necessary to stress the importance of prevention and good hearing hygiene.

      To avoid having bothersome phenomena such as tinnitus or varying 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 impaired hearing. concerts and nightclubs, such as not getting too close to the speakers. . If you are working in a noisy environment, such as a job site with drills, headphones should be used. protection.

      Bibliographical references:

      • Knipper M, Van Dijk P, Nunes I, Rüttiger L, Zimmermann U (2013). Advances in the neurobiology of hearing disorders: recent developments based on 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 the key to generating hyperacusis or tinnitus? J Neurophysiol. 111 (3): 552-64. doi: 10.1152 / jn.00184.2013.

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