of cochlea Also known as part of the nerves. vestibular cochlea Or the auditory nerve, which is a sensory nerve responsible for hearing. It travels from the cochlea, a spiral-shaped structure in the inner ear, to the brainstem as part of the eighth cranial nerve. The other part of cranial nerve VIII is called the vestibular nerve and helps with balance.
Cochlear nerve problems can be caused by inflammation, infection, injury, or a tumor (acoustic neuroma). In rare cases, some people are born without a cochlear nerve or have a shortened cochlear nerve. Approximately 20% of childhood hearing loss is associated with cochlear nerve defects.
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anatomy
The cochlear nerve is a purely sensory nerve (has no motor or motor functions) and is one of two parts of the vestibulocochlear nerve, also known as the eighth cranial nerve (VIII). The cochlear nerve is responsible for hearing. The vestibular nerve is responsible for balance, movement, and position.
structure
To understand the structure of the cochlear nerve, it is best to start with the anatomy of the ear.
The ear has three main parts.
External ear: Includes the pinna (the fleshy, visible part of the ear) and the external auditory canal. Middle ear: Includes the three ear bones (called the ossicles), the eardrum (also called the tympanic membrane), and the pinna. Eustachian tube
Inner ear: includes the cochlea, cochlear nerve, and vestibular organs.
The inner ear is located in the hollow part of the temporal bone (located at the side and bottom of the skull). The cochlea is a spiral organ containing fluid (perilymph and endolymph) located in the inner ear.
The cochlea houses the cell bodies of the cochlear nerves within an area called the spiral ganglion. Process the sound in the following way:
Nerve cells (neurons) in the spiral ganglion project sound signals to small hair cells, also located in the cochlea. Hair cells convert sound signals into nerve impulses, which are transmitted to the brainstem by the cochlear nerve trunk. The impulse eventually reaches the brain. Brain for interpretation.
The average number of auditory nerve fibers varies between 500 and 1400 per millimeter (mm), depending on their location within the cochlea. In a healthy cochlea, there are a total of 30,000 fibers.
Can you hear without the cochlear nerve?
Cochlear implants can be used to help with hearing by stimulating the auditory nerve endings, but only if the cochlear nerve is still functioning and the hearing loss is due to other causes. A surgery called an auditory brainstem implant (ABI) can be used in people with a malfunctioning cochlear nerve, but with varying degrees of success.
position
The cochlear nerve trunk runs from the base of the cochlea through the internal auditory canal to the brainstem. Within the internal auditory canal, the cochlear nerve trunk joins with the vestibular nerve to form cranial nerve VIII.
When the cochlear nerve enters the brainstem, it innervates, or supplies nerve signals to, the cochlear nucleus, located at the pontomedullary junction (where the pons of the brainstem meets the medulla oblongata).
The cochlear nerve exits the skull at the temporal bone, and information from the cochlear nucleus is carried to the brain’s primary auditory (auditory) cortex for sound analysis.
function
The cochlear nerve is a sensory nerve that allows us to hear. This complex and precise job begins and ends with the following steps:
of auricle Sound waves are collected inside the ear and travel through the ear canal to the eardrum. The waves cause the eardrum to vibrate. Vibrations from the eardrum cause the bones of the ear (malleus, incus, and stapes) to begin to move. This movement stimulates cochlear neurons (in the spiral ganglion) to form synaptic connections with hair cells (as well). Hair cells convert sound vibrations into electrochemical (neural) signals. The nerve signals are then relayed through the cochlear nerve and into the brainstem. The signals are carried from the brainstem to the brain’s auditory cortex, where they are interpreted and “heard.”
Related conditions
Cochlear nerve damage can occur for a variety of reasons. The cochlear nerve can be affected by inflammation due to autoimmune diseases, trauma, congenital malformations, tumors, infections, and vascular damage.
Depending on your specific condition, you may experience the following symptoms:
Vertigo, feeling like the world is spinning around you
nystagmusor rapid uncontrolled eye movements
tinnitusa ringing or buzzing sound in the ear Sensorineural (often age-related) hearing loss
Conditions that can affect the cochlear nerve include:
vestibular labyrinthitis
vestibular labyrinthitis It involves swelling of the vestibulocochlear nerve (both vestibular and cochlear nerves).
Symptoms include sudden and severe dizziness, hearing loss, ringing in the ears, and balance problems. The cause of this condition may be related to viral infections such as herpesvirus, influenza, measles, mumps, and hepatitis.
multiple sclerosis
Approximately 1 in 100 people diagnosed with the autoimmune disease multiple sclerosis (MS) experience hearing loss as a result of MS lesions (sites of inflammation) in the cochlear nerve or elsewhere in the auditory pathway. Masu. MS can mean you are at higher risk for hearing loss, but hearing loss can also be a sign of previously undiagnosed MS.
In MS, a person’s own immune system mistakenly attacks the insulating covering, causing inflammation (myelin) Damage to nerve fibers in the brain, spinal cord, and/or eyes. When the cochlear nerve is affected, patients may experience sudden hearing loss and dizziness.
acoustic neuroma
Slow-growing tumors of Schwann cells that insulate the vestibulocochlear nerve can cause progressive hearing loss, tinnitus, and dizziness.
This non-cancerous tumor (called a vestibular tumor) schwannoma Acoustic neuroma) usually occur in one cochlear nerve. If the tumor occurs on both sides, it may be a sign of a genetic disorder called neurofibromatosis type 2.
Anterior inferior artery small stroke
Microstrokes affect the vestibulocochlear nerve (when the nerve’s blood supply is cut off) and can cause sudden unilateral hearing loss and dizziness. Posterior circulation strokes can cause symptoms similar to those of vestibular neuritis with nausea.
Depending on the severity of the stroke, other symptoms may also occur, such as loss of coordination, difficulty walking, and weakness or numbness on one side of the face.
trauma
Labyrinth concussions and other trauma to the temporal bones (e.g., a blow to the side of the head) can damage the cochlear nerve in the inner ear and cause hearing loss. Keep in mind that damage can also occur from acoustic trauma, chronic or loud noise exposure.
congenital malformation
Congenital malformations of the cochlear nerve (agenesis (no nerve) or hypoplasia (small nerve)) are a rare cause of sensorineural hearing loss.
Certain genetic mutations (changes) can also narrow the neural tube within the cochlea, leading to hearing loss and other structural problems.
process
Treatment depends on the specific cause affecting the cochlear nerve. Hearing tests, imaging tests, and other diagnostic tests may be required. Treatments include:
Vestibular labyrinthitis: Symptoms can be controlled with medications, such as Antivert (meclizine) for dizziness and Zofran (ondansetron) for nausea. Steroids may be given to treat hearing loss, and antiviral drugs such as Zovirax (aciclovir) may be given if the cause is suspected, such as shingles. If your symptoms persist for more than a few weeks, you may need a balance rehabilitation program. MS-related inflammation: Effects on the cochlear nerve often require patients to take corticosteroids. Long-term treatment of MS requires disease-modifying therapies, such as injectable interferon and injectable drugs like Ocrevus (ocrelizumab). Acoustic neuroma: There are three treatment options: observation, radiation therapy, or surgery. The goal of radiation therapy is to slow the growth of the tumor while surgery removes it completely. Stroke: Stroke requires immediate treatment, including thrombolysis with tissue-type plasminogen activator. Brain swelling should be monitored. If your stroke is caused by a blood clot (called an ischemic stroke), you may need anticoagulants.
Cochlear nerve trauma: In cases of severe trauma or hypoplasia or hypoplasia of the cochlear nerve, cochlear implants may restore hearing by transmitting sound signals from the patient’s inner ear to the brain. Results vary.
summary
The cochlear nerve, part of cranial nerve VIII, is a sensory nerve responsible for hearing. Nerve damage or destruction can cause symptoms such as hearing loss, tinnitus, dizziness, and nausea.
Symptoms and treatment vary depending on what is affecting the cochlea. These causes may include infections, underlying diagnoses such as multiple sclerosis, congenital or genetic conditions, and injuries. Treatment options include medications, surgery, and cochlear implants.