Cranial nerves: anatomy, location and function

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The cranial nerves are an important collection of nerves that travel directly to the brain, not through the spinal cord like most other nerves. They are called cranial nerves because they originate from and are found within the skull or skull. The cranial nerves have several critical functions in everyday life and are therefore an important focus of attention for healthcare professionals, as well as for patients with cranial nerve dysfunctions.

Unless you are a healthcare professional, it is generally not necessary to know all the details about each nerve individually. However, understanding the cranial nerves can help you locate the source of the specific problems you are experiencing. This can help you get more information and get the right medical care.

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Anatomy of the cranial nerve

All the cranial nerves are located in the lower part of the brain within the skull. They come in pairs, one on each side of the brain, and are numbered with Roman numerals I through XII. They are often referred to as CN I, CN II, etc. The first two cranial nerves, the olfactory nerve and the optic nerve, leave the brain, while the other ten nerves originate from the brain stem. The nerves then travel from their source to various parts of the body in the head, face, mouth, and in some cases around the periphery of the body.

Some specialists recognize an extracranial nerve called the terminal nerve or null cranial nerve. This nerve is a small, often microscopic nerve plexus around the olfactory nerve. It was originally thought to support the function of smell, but it is now known that the terminal nerve does not enter the olfactory bulb and does not participate in the sense of smell. Rather, it is believed that this nerve may be a rudimentary anatomical structure and may play a role in regulating sexual function.

Function

The cranial nerves transmit various information to and from the body. Some nerves are motor and move muscles. The rest are sensory nerves; they carry information from the body to the brain. Certain cranial nerves are a combination of motor and sensory nerves.

Each pair of cranial nerves has a specific purpose in your body and functions as a motor nerve, a sensory nerve, or both. Nerves can be affected by a variety of conditions, and certain signs and symptoms can appear in your body as a result of a cranial nerve injury or problem.

Olfactory nerve (NC I)

The olfactory nerve is in charge of transmitting everything we feel to the brain. This nerve runs from the brain to the olfactory bulb, where smells are analyzed. Violations of this nerve can cause anosmia, an inability to pick up odors . It also greatly affects our sense of taste .

Optic nerve (NC II)

The optic nerve transmits electrical signals from the retina to the brain, which converts these signals into an image of what we see in the world around us. Optic nerve disorders, such as optic neuritis , can lead to visual impairment, double vision, and blindness .

Oculomotor nerve (CN III)

The common ocular motor nerve has two main functions. First, the common ocular motor nerve transmits signals that allow the eyes to move in all directions that are not controlled by other cranial nerves. Second, the common ocular motor nerve carries parasympathetic fibers to the iris , causing the iris to narrow in bright light. Damage to the common ocular motor nerve can not only cause double vision (diplopia), it can also cause a 'swollen pupil', a pupil that cannot be narrowed. Due to its location, the common ocular motor nerve is susceptible to damage from increased intracranial pressure, and a dilated pupil can be a sign of a serious neurological disorder .

Trochlear nerve (CN IV)

The blocked nerve controls the muscle that moves the eyeball down and out. Damage to this nerve can cause diplopia, which can be improved by tilting the head away from the affected eye .

Trigeminal nerve (CN V)

The trigeminal nerve is primarily a sensory nerve, that is, it transfers sensations from the face to the brain. Also, the trigeminal nerve controls some of the facial muscles that are important for chewing. One of the most serious complications of the trigeminal nerve is trigeminal neuralgia , an extreme form of facial pain. It can be caused by a virus or mechanical irritation due to rubbing of a bundle of blood vessels near the nerve .

Nerve abducens (CN VI)

This nerve controls the muscle that moves the eyes away from the nose. Damage to the abducens nerve causes double vision, in which one image is directly adjacent to the other. Sometimes the abducens nerve can be affected on both sides in cases of increased intracranial pressure, for example with pseudotumor of the brain .

Facial nerve (CN VII)

The facial nerve is complex. Not only does it control most of the muscles in the face; This nerve also transmits taste signals from the front of the tongue, transmits parasympathetic fibers that cause the eyes to water and salivate in the mouth, and is responsible for small sensations around the ear. It also helps regulate hearing by controlling the impulsive muscle. This is why facial nerve inflammation, such as Bell's palsy , can lead to more problems than just facial weakness, although weakness is often the most obvious symptom .

Vestibulocochlear nerve (CN VIII)

This nerve has two main components: the cochlear component transmits acoustic information to the brain so that we can hear, and the vestibular part sends signals about balance and movement. Vestibulocochlear nerve problems can cause hearing loss or dizziness , and often both. A common problem associated with the eighth nerve is acoustic neuroma . This benign tumor can press on the nerve and cause hearing loss or dizziness .

Glossopharyngeal nerve (NC IX)

The lingopharyngeal nerve performs many random tasks. This nerve is responsible for taste sensations in the back of the tongue, sensations in a small part of the ear, as well as parts of the tongue and throat, innervation of a muscle important for swallowing (shilopharyngeus), and salivation of the parotid gland. It also receives important information about blood pressure from chemoreceptors and baroreceptors in the body from the carotid artery. Lingopharyngeal nerve irritation can lead to lingopharyngeal neuralgia, a condition in which swallowing is very painful .

Vagus nerve (CN X)

This nerve governs the pharynx (for swallowing) and larynx (for speaking), as well as sensations from the pharynx, a portion of the meninges, and a small portion of the ear. Like the glossopharyngeal nerve, the vagus nerve senses taste (from the throat) and also picks up specific signals from chemotherapy and baroreceptors near the heart (in the aortic arch). In addition, the vagus nerve transmits parasympathetic fibers to the heart, the signals of which can slow down the heartbeat. Due to its connection to the heart , vagus nerve disorders can be very dangerous. On the other hand, vagus nerve stimulation has been shown to be potentially beneficial in a wide range of diseases, including epilepsy .

Accessory spinal nerve (CN XI)

The spinal accessory nerve is less complex than its immediate predecessors. It has only one main function: to induce contraction of the sternocleidomastoid muscle and the trapezius muscle to help move the head or shoulder. Diseases of this nerve affect the ability of these muscles to use them . A simple test of accessory nerve function is just a shrug. If you cannot lift a shoulder, the accessory nerve may be damaged.

Hyoid nerve (CN XII)

The hypoglossal nerve is the motor nerve that controls all movements of the tongue. Difficulty speaking (dysarthria) or moving food in the mouth are possible consequences of hypoglossal nerve damage .

Treatment of cranial nerve injuries.

If you have a problem or suspect a problem with your cranial nerve, you should see your doctor immediately. Because there are nerves within the skull, treatment often involves focusing on protecting your brain, helping to correct nerve damage. Some treatments for cranial nerve disorders include surgery. Of course, this is risky and should be used as a last resort. Certain cranial nerve problems, such as tumors, can be successfully treated with radiation. A focused beam of radiation can help shrink or eliminate a tumor that affects the cranial nerve.

Bottom line: If you have any symptoms with movement or sensation around your head and face, you should seek immediate medical attention. By getting an early diagnosis and starting the proper treatment, you will increase your chances of a full recovery from your cranial nerve problem.

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