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The cranial nerves belong to the peripheral nervous system. There are 12 pairs of them. Each of them performs different functions, e.g. some perceive facial sensations, and others control the activities of the oculomotor muscles. What are cranial nerves, what can damage them and how do cranial nerve disorders manifest themselves?

The cranial nerves(Englishcranial nerves ) are a component of the peripheral nervous system. They were first mentioned at the beginning of our era, when Galen described the existence of seven pairs of these structures in humans. Many, many years later, only in 1664, the British anatomist Thomas Willis drew attention to the fact that in humans there are, however, 9 pairs of cranial nerves. Full knowledge about this part of the peripheral nervous system was not really acquired until the next century, when in 1778, an anatomist of German origin, Samuel Soemmering, described and named 12 pairs of cranial nerves.

Contents:

  1. Cranial nerves: olfactory nerve
  2. Cranial nerves: optic nerve
  3. Cranial nerves: oculomotor nerve
  4. Cranial nerves: block nerve
  5. Cranial nerves: trigeminal nerve
  6. Cranial nerves: abduction nerve
  7. Cranial nerves: facial nerve
  8. Cranial nerves: vestibulocochlear nerve
  9. Cranial nerves: glossopharyngeal nerve
  10. Cranial nerves: vagus nerve
  11. Cranial nerves: accessory nerve
  12. Cranial nerves: sublingual nerve
  13. Cranial nerves: causes and symptoms of damage
  14. Cranial nerves: research

The cranial nerves can play the role of both sensory and sensorimotor nerves. They differ from each other in terms of the tasks they perform, where they originate from and how they proceed later.

Cranial nerves: olfactory nerve

The first cranial nerve is the olfactory nerve (Englisholfactory nerve ). As the name suggests, it is responsible for the sense of smell. The olfactory nerve cells are located in the olfactory epithelium. Nerve fibers from the olfactory nerve pierce the ethmoid plate of the ethmoid bone and eventually travel to the olfactory bulb. The olfactory nerve is a purely sensory nerve.

Cranial nerves: optic nerve

Optic nerve optic nerve ) is the second cranial nerve. The bodies of the nerve cells of the optic nerve in this case are located in the ganglion layer of the retina. The axons of cells belonging to the optic nerve run in the optic canal towards the base of the brain. There they connect to the nerve from the opposite side, and this is where the optic crossing occurs. Some of the fibers cross, some do not, and they form visual strands that ultimately lead to the subcortical visual centers. Like the olfactory nerve, the optic nerve is a sensory nerve and its function is to perceive visual stimuli - it is thanks to it that we are able to see.

Cranial nerves: oculomotor nerve

The third cranial nerve is the oculomotor nerve (Englishoculomotor nerve ). The cell bodies of this nerve are located in two nuclei, which are the oculomotor nucleus and the Westphal-Edinger nucleus. This nerve originates in the midbrain and enters the eyeball through the superior orbital fissure. It has two important functions. Responsible for the pupil's reaction to light and controls the activity of, inter alia, the parts of the muscles that control the movement of the eyeballs. It innervates the levator of the upper eyelid, the sphincter muscle of the pupil and the ciliary muscle, and in addition it supplies the majority of the external muscles of the eyeball in motion (all except the lateral and oblique upper muscles). In general, the oculomotor nerve is considered to have a mixed sensorimotor function.

Cranial nerves: block nerve

The trochlear nerveis the fourth cranial nerve. It controls the function of the upper oblique muscle of the eyeball. Nuclei of nerve cells are located in the trochlear nucleus, and the axons derived from it go to the orbit through the superior orbital fissure. The block nerve is a sensorimotor nerve.

Cranial nerves: trigeminal nerve

The trigeminal nerveis the fifth cranial nerve. This nerve has several nuclei: the trigeminal ganglion, the motor nucleus of the trigeminal nerve, and the mesencephalic nucleus of the trigeminal nerve. It is a sensorimotor nerve and has three branches. The first one is the optic nerve, which is responsible for the perception of sensory sensations in the upper part of the head - forehead, upper eyelids and the upper surface of the scalp. The second branch of the trigeminal nerve is the maxillary nerve, which is responsible for the perception of sensory experiences in the middle part of the face - the cheeks, upper lip and nasal cavity. The third branch of the trigeminal nerve is the mandibular nerve, which deals with the reception of sensory stimuli from the area of ​​the ears, chin and lower lip.and managing the activity of the mandibular muscles.

Cranial nerves: abduction nerve

The sixth cranial nerve is theabducens nerve . The bodies of his nerve cells are located in the abduction nucleus, and this nerve itself innervates the lateral rectus muscle of the eye. Like the block and oculomotor nerves, the abduction nerve reaches the eyeball area through the superior orbital fissure. It is a mixed sensorimotor nerve.

Cranial nerves: facial nerve

The facial nerve ( facial nerve ) is the seventh cranial nerve that begins in the superior salivary ganglia, facial ganglia, and the knee ganglion. This nerve is also a mixed, sensorimotor nerve and it innervates various glands (submandibular and sublingual glands, but also the lacrimal gland). The facial nerve is also responsible for the perception of sensory impressions from the area of ​​the auricle and for the perception of taste stimuli from the front 2/3 of the tongue. The seventh cranial nerve also supplies most of the facial muscles.

Cranial nerves: vestibulocochlear nerve

The eighth cranial nerve is the vestibulocochlear nerve (Englishvestibulocochlear nerve ). The bodies of his nerve cells are located in the vestibular and spiral ganglia. It is another cranial nerve with a mixed sensorimotor function. It is responsible for the sense of balance and for receiving the impulses that ultimately enable us to hear.

Cranial nerves: glossopharyngeal nerve

The glossopharyngeal nerveis the ninth cranial nerve. It begins in several structures: the inferior salivary nucleus, the ambiguous nucleus and two glossopharyngeal ganglia: the upper and the lower. The glossopharyngeal nerve is a sensorimotor nerve and it innervates the parotid gland and the glossopharyngeal muscle. In addition, it is responsible for the perception of sensory experiences from the back 1/3 of the tongue and around the outer ear.

Cranial nerves: vagus nerve

The tenth cranial nerve is the vagus nerve ( vagus nerve ). It has an exceptionally many different functions. Its fibers extend from the skull to the parts of the digestive tract located far away from it. The nerve cell bodies of the vagus nerve are located in the dorsal and ambiguous nuclei, and in the ganglia of the upper and lower vagus nerves. It is responsible for the innervation of the pharyngeal and laryngeal muscles, and the vagus nerve also supplies the structures of the gastrointestinal tract with sympathetic innervation. Along with the glossopharyngeal nerve, the vagus nerve also takes care of sensory sensations from the outer ear. How can you alreadyIt's easy to guess that the vagus nerve - like most other cranial nerves - contains both sensory and motor nerve fibers.

Cranial nerves: accessory nerve

The accessory nerve (Eng.accessory nerve ) is the eleventh cranial nerve. It is peculiar in a way because its nerve cell bodies are located both in the ambiguous nucleus and in the anterior horns of the first six spinal cord segments. The accessory nerve is a mixed nerve and it receives sensory stimuli and provides motor supplies to the sternocleidomastoid and trapezius muscles.

Cranial nerves: sublingual nerve

The last, twelfth cranial nerve is the sublingual nerve ( hypoglossal nerve ). It begins in the sublingual nucleus and it innervates the own muscles of the tongue and one more muscle - the chin-lingual muscle.

Cranial nerves: causes and symptoms of damage

There are relatively many potential causes of cranial nerve damage. Disorders of the activity of these structures can be caused both by the disruption of their continuity, as well as compression of the nerve fiber or damage to the testes, in which the bodies of nerve cells of one of the cranial nerves are located.

The diseases in which the course of the cranial nerves may be damaged include:

  • stroke (both ischemic and haemorrhagic),
  • multiple sclerosis,
  • head injuries,
  • iatrogenic damage (e.g. made during some neurosurgical operation),
  • inflammation,
  • tumors of the central nervous system.

Symptoms of cranial nerve damage depend on the exact nerve involved in the pathological process. For example, damage to the optic nerve may result in visual disturbances (including blindness), damage to the trigeminal nerve may lead to the deviation of the mandible, and the facial nerve may lead to loss of facial expressions or loss of taste from the front part of the tongue.

Cranial nerves: research

The examination of the cranial nerves is one of the elements of the neurological examination. During it, the activity of individual cranial nerves is assessed in turn:

  • the olfactory nerve is examined by asking the patient to name different smells,
  • the optic nerve is assessed by checking whether the patient can see at all and what his field of view is,
  • nerves: oculomotor, block and abduction nerves can be examined during the assessment of eye movements,
  • examination of the trigeminal nerve is based on the assessment of mandibular mobility and sensationparticular areas of the face,
  • the facial nerve is assessed by assessing the taste sensation in the front part of the tongue and asking the subject to frown,
  • the vestibulocochlear nerve is examined by assessing hearing,
  • the glossopharyngeal nerve is examined by assessing the position of the uvula in the throat,
  • dysfunction of the vagus nerve may be evidenced by speech articulation disorders,
  • the accessory nerve is examined by asking the patient to shrug,
  • and the sublingual nerve function is assessed after the patient is asked to perform various movements with his tongue.
About the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.

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Neurology