Cranial nerves

Cranial nerves are nerves emerging from the brain stem or entering into it. A person has 12 pairs of cranial nerves (nervi craniales). They are denoted by Roman numerals in accordance with the order of their location. Each nerve has its own name:

• I paranasensitive nerves (nn. Olfactorii)
• II paraplegic nerve (n. Opticus)
• III paraplegin-motor nerve (n. Oculomotorius)
• IV parabolic nerve (n. Trochlearis)
• V paraplegic nerve (n. Trigiinus)
• VI parasitive nerve (n. Abducens)
• VII pair - facial nerve (n. Facialis)
• VIII parapod-cochlear nerve (n. Vestibulocochlearis)
• IX para-glossopharyngeal nerve (n. Glossopharyngeus)
• X paralytic nerve (n. Vagus)
• XI pair - additional nerve (n accessorius)
• XII para-hyoid nerve (n. Hypoglossus)

Cranial nerves innervate all the organs of the head. On the neck, the area of their innervation extends to the esophagus and trachea. In addition, the vagus nerve innervates the intestines located in the thoracic and abdominal cavities (up to the transverse colon).

All cranial nerves do not have the correct segmental arrangement. In contrast to similar in origin and development of spinal nerves, the cranial nerves are divided into several groups, different in their development, structure and function.

The first group is the nerves of the senses. This group includes the olfactory (I pair), visual (II pair) and pre-vertebral (VIII pair) nerves. The olfactory and optic nerves develop as outgrowths of the anterior cerebral bladder. These nerves do not have peripheral sensory nodes.

The second group is the motorized cranial nerves: the oculomotor (III pair), the block (IV pair), the diverting (VI pair) and the sublingual (XII). By origin and function, they correspond to the anterior roots of the spinal nerves. The posterior roots of these nerves do not develop. The sublingual nerve innervates the muscles of the tongue.

The third group of cranial nerves (nerves of gill arches) is represented by the trigeminal (V pair), facial (VII pair), lingopharyngeal (IX pair), wandering (X pair) and accessory (XI pair) nerves. Primarily, each of these nerves innervates one of the fetal arches of the embryo, and subsequently its derivatives. The nerves of the gill arches are organized in accordance with the principles of metamerism, since gill arches are laid in the form of metameric formations, forming a series of successive similar structures. These nerves are deprived of the anterior and posterior roots, all their roots leave the brainstem on the ventral surface of the brain. Cranial nerves, unlike cerebrospinal nerves, do not form plexuses, they have connections only along the periphery, on the routes to the innervated organs.

Sensitive parts of the nerves of the branchial arches have nerve nodes (ganglia) in which the bodies of peripheral sensory neurons are located. Sensitive ganglion of the trigeminal and facial nerves are found in the cavity of the skull, the lingopharyngeal and vagus nerves - outside the skull.

Some cranial nerves (III, IV, VII, X pairs) contain vegetative parasympathetic fibers, which are the processes of the autonomic nuclei of these nerves located in the brain stem. These fibers terminate in the parasympathetic nodes that are at the periphery near the internal organs or in their thickness. In the cranial nerves there are sympathetic fibers that join them in the branches of the sympathetic trunk or from the circulatory sympathetic plexuses. Vegetative fibers can pass from one cranial nerve to another.

Cranial nerves are laid in the fetus very early (from the 5th to the 6th week). Myelination of nerve fibers occurs first of all in the vestibular nerve (at 4 months), in most of the remaining nerves - at the 7th month.