Cranial nerves

Cranial nerves arise directly from the brain. Most of them are in the brain stem. The task of the cranial nerves is to form the center of the nervous system in the head, neck and trunk area.

What are cranial nerves?

Twelve run through both halves of the body Cranial nerves that perform a specific function. Each nerve is assigned a number according to the Roman number system. Eleven of the twelve nerves share the common feature that they arise from the brain or that they do not leave it in the first place. The exception is the Accessory nerve (XI). It arises from the spinal cord, but is still classified as a cranial nerve. In terms of expression, cranial nerves are comparable to peripheral nerves. Peripheral nerves are responsible for supplying the body. There are deviations in the first two cranial nerves Olfactory nerve (I) and at Optic nerve (II). They are immediate protrusions of the cerebrum.

Cranial nerves also have the property that they lie in pairs. They can contain somatomotor and vegetative fibers and thus cover a different area of ​​responsibility. Somatomotor fibers enable conscious voluntary movement. In contrast, vegetative fibers are required for unconscious automatic reactions.

Anatomy & structure

In terms of anatomy, a cranial nerve consists of a bundle of nerve fibers. This is enveloped by connective tissue and protected from the forces of the environment. The aim of the nerves is to transmit impulses over longer stretches of distance. Information is transmitted from nerve cell to nerve cell along a nerve fiber.

A nerve cell, in turn, consists of a dendrite that is supposed to absorb stimuli from the environment via a branch system. The recorded signals are passed on to the cell body and the axon hillock on it. If a sufficient intensity is reached, the information transfer can be continued.

For this purpose, the signals are transported as electrical impulses along the axon. Finally, the signal reaches a synapse. This is where the information is passed on to the next nerve cell. This process repeats itself until the end of the nerve fiber is reached. Then the cranial nerves have reached their destination or they branch off into peripheral nerves. In their entirety, the cranial nerves form an important part of the central nervous system.

Function & tasks

Each cranial nerve has its own task.

The first, referred to as Olfactory nerve (I), for example, has the function of conveying possible olfactory sensations through the nose. Accordingly, it is also referred to as the olfactory nerve. thanks to the Optic nerve (II) vision is possible with the eyes. The optic nerve forwards the recorded images to the brain. In its function, the optic nerve is controlled by the Oculomotor nerve (III), the Trochlear nerve (IV) and the Abducens nerve (VI) added. The three nerves are responsible for making eye movements and controlling eye muscles. That also plays an important role Trigeminal nerve (V). Its main task is to transmit stimuli from the head area to the brain. He is also responsible for controlling the masticatory muscles. It consists of three strong nerve branches and is therefore known as the triple nerve. The coordination of the facial expressions takes over Facial nerve (VII). In addition, it enables the perception of flavors. We owe the sense of hearing and balance to this Vestibulocochlear nerve (VIII). It runs between the inner ear and the brain. Muscles of the throat are over the Glossopharyngeal nerve (IX) controlled. He is also responsible for the swallowing reflex. Of the Vagus nerve (X) regulates the heart rate and supplies the larynx. In addition, it supports gastric acid secretion. The neck and neck muscles are connected to the Accessory nerve (XI) controlled. Finally, the Hypoglossal nerve (XII) a large part of the tongue muscles are accessed. The most important tasks include sticking out the tongue and swallowing.

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Diseases

Diseases of the cranial nerves can be attributed to various deficits and impairments of the nervous system. Depending on the affected cranial nerve, various symptoms are conceivable. A failure of the Olfactory nerve (I) is associated, for example, with a weakening of the olfactory sensation. This is known as anosmia. Anosmia can occur with a fractured skull base.

A disorder of the optic nerve (II) leads to a loss of the visual field. This can be caused by high pressure inside the skull. The visual field restriction is called quadrant anopia in technical terms.

A restriction in eye movements occurs when the oculomotor nerve (III) is obstructed. Then the pupils dilate and the eyes become paralyzed. If the trochlear nerve (IV) or abducens nerve (VI) fails, patients also complain of a decrease in visual acuity and the perception of double vision.Sensitivity disorders in the head are particularly a problem when the trigeminal nerve (V) is damaged.

This is accompanied by hearing difficulties called hypacusis. Paralysis of the face also occurs with a disorder of the facial nerve (VII). In addition, there is a weakening of the taste sensation. Failures in the vestibulocochlear nerve (VIII) lead to hearing loss, in the glossopharyngeal nerve (IX) they lead to swallowing disorders and in the vagus nerve (X) hoarseness is the result of a disorder.

After ENT interventions, the accessory nerve (XI) can be damaged. A tilt of the head is then the consequence. Speech disorders and swallowing difficulties occur when the functionality of the hypoglossal nerve (XII) is restricted. Often it is no longer possible to stick out the tongue.