Anatomy & Organs

Cranial nerves – structure, function & diseases

Brain nerves

Cranial nerves arise directly from the brain. Most of these are in the brainstem. 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 cranial nerves run through both halves of the body and have a specific function. Each nerve is given a number based on the Roman numeral system. Eleven of the twelve nerves share the common feature that they originate from the brain or don’t leave it at all. The accessory nerve (XI) is an exception. 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 the supply of the body. Deviations occur in the first two cranial nerves, the olfactory nerve (I) and the optic nerve(II). They are direct protuberances of the cerebrum .Cranial nerves also have the property that they are paired. They can contain somatomotor and vegetative fibers and thus cover a different range of tasks. Somatomotor fibers allow for conscious voluntary movement. In contrast, vegetative fibers are needed for unconscious automatic responses.

Anatomy & Structure

Anatomically, a cranial nerve consists of a bundle of nerve fibers . This is encased by connective tissue and protected from the forces of the environment. The aim of the nerves is to transmit impulses over long distances. Information is transmitted from nerve cell to nerve cell along a nerve fiber .A nerve cell in turn consists of a dendrite , which 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 lying on it . If a sufficient intensity is reached, the information transmission 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 arrived at their destination or they branch off into peripheral nerves. Collectively, the cranial nerves form an important part of the central nervous system .

Function & Tasks

Each cranial nerve has its own task.

The first, known as the olfactory nerve (I), for example, has the function of conveying possible olfactory sensations via the nose . Accordingly, it is also referred to as the olfactory nerve. Thanks to the optic nerve (II), seeing with the eyes is possible. The optic nerve transmits the recorded images to the brain. The function of the optic nerve is complemented by the oculomotor nerve (III), the trochlear nerve (IV) and the abducens nerve (VI). The three nerves are responsible for performing eye movements and controlling eye muscles . It also plays an important roleTrigeminal nerve (V). Its main task is to transmit stimuli from the head area to the brain. It is also responsible for controlling the chewing muscles. It consists of three strong nerve branches and is therefore referred to as the triplet nerve. The facial nerve (VII) coordinates facial expressions . In addition, it enables the perception of flavors . We owe our sense of hearing and balance to the vestibulocochlear nerve (VIII). It runs between the inner ear and the brain. Muscles of the pharynx are attached via the glossopharyngeal nerve(IX) controlled. It is also responsible for the swallowing reflex. The vagus nerve (X) regulates the heart rate and supplies the larynx . It also supports the secretion of gastric acid . The neck and neck muscles are controlled by the accessory nerve (XI). Finally, much of the tongue musculature is accessed via the hypoglossal nerve (XII). Sticking out the tongue and swallowing are among the most important tasks.

Diseases

Diseases of the cranial nerves can be traced back to various failures and impairments of the nervous system. Depending on the affected cranial nerve, various symptoms are conceivable. A failure of the olfactory nerve (I), for example, is accompanied by a weakening of the sense of smell. This is called anosmia . Anosmia can occur with a skull base fracture .A disturbance 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 referred to in technical terms as quadrant anopia.

Restriction of eye movements occurs when the oculomotor nerve (III) becomes obstructed. Then the pupils dilate and the eyes become paralyzed. If the nervus trochlearis (IV) or the nervus abducens (VI) fails, patients also complain about a decrease in visual acuity and the perception of double vision . Sensory disturbances in the head are a problem in particular 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. Deficiencies 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.

Damage to the accessory nerve (XI) can occur after ENT interventions. The result is that the head is tilted. Speech disorders and swallowing difficulties occur when the functionality of the hypoglossal nerve (XII) is impaired. It is then often no longer possible to stick out the tongue.

Website | + posts

Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.