The cranial nerves are also called cranial nerves. There is a tendency to be identified with Roman numerals according to the order in which they are, although they are also identified from quite specific names referring to their functionalities or location.

In the following article, we will delve into what and what are the cranial nerves as well as the disorders and diseases that can occur associated with these nerves.

What are cranial nerves?

In Calle and Casado’s research titled Cranial Nerve Exploration,” these are defined as the components of the Peripheral Nervous System (PNS) that emerge from the brainstem. There are some authors who exclude olfactory and optic because they are considered extensions of thebrain.

Cranial nerves exert significant functions in our organism and are often mistakenly thought of as a cranial division.

Types of cranial nerves

The 12 pairs of cranial nerves existing in our Peripheral Nervous System are organized based on their origin and functionality. In this way, they are grouped into structures to understand them and thus know in greater depth the meaning of our brain.

According to its origin

According to their origin or position, cranial nerves are organized from Roman numerals, which identify each pair in question with its location in the brainstem. I mean:

  • Cranial nerve I and pair II are located above the brainstem.
  • Pair III and IV from themidbrain.
  • V, VI, VII and VIII from the brainstem bridge.
  • And cranial nerves IX, X, XI and XII are from the medulla oblongata.

According to your function

This organization focuses on the functionality of cranial nerves. And they are associated with them, although they are also identified globally with the Roman numerals in order to identify which pair is being talked about.

  • Par I, II and VIII are those that fulfill sensitive functions.
  • Par III, IV and VI are associated with ocular and eyelid mobility.
  • Cranal nerve XI and XII is the activation of the muscles in the neck and tongue.
  • Cranial nerve X, V, VII, and IX are considered mixed function.

Classification and function of the cranial nerves

Likewise, from the general description that we have just obtained, the cranial nerves are classified by specific functions. Below we will describe each of them more precisely, to allow us to understand more accurately the origin of its importance and essentiality in the performance of our daily lives.

Olfactory Nerve

This nerve in the investigation entitled ” Exploration of the cranial nerves “ , it is exposed that this nerve is a specialized extension of the brain, which collects the olfactory sensitivity of the nasal receptors and conducts it through its components to achieve the integration of information olfactory.

To assess the functionality of this nerve, it is initially verified that both nostrils are open, occluding each one interchangeably and asking the patient to breathe through the other.

After that, the process is repeated but with the eyes closed so that it identifies a common odor, avoiding that they are irritating to the nostrils.

Optic nerve

It is the nerve that conducts visual impulses from the retina, where it converts electrical signals through the optic nerves and their different segments. It is in charge of controlling vision.

For evaluation, the patient is kept in a well-lit room and on a chart.

It is important to mention that if the individual wears glasses normally, they must have them during the test. One of the eyes should then be covered and read the small letters on the chart and then do the same with the other eye.

Nerve Motor

They are responsible for the movements of four of the six extraocular muscles. It also controls pupillary reactions and elevation of the upper eyelid.

It is located in the anterior portion of the gray matter and provides information through its components. It can also be recognized as the oculomotor cranial nerve.

pathetic nerve

It is the IV nerve and originates in the midbrain, following a course below the cerebellum and perforating the dura matertag. It is difficult to visualize due to its small size and can be divided into four parts:

  • Core segment
  • Cisternal segment
  • Cavernous sinus segment
  • extraforaminal segment

Trigeminal Nerve

It is the thickest cranial nerve and collects all facial sensitivity, also including both nasal and oral mucosa, as well as being the nerve that is in charge of the chewing process.

It is made up of three branches: ophthalmic, maxillary, and mandibular. It is also responsible for the corneal reflex along with the facial nerve, since it has both motor and sensory axons.

Oculomotor Nerve

It is the IV pair and comes from a group of neurons located medially in the lower part of the pons. It controls the lateral deviation of the eye and may also be known as the abducens nerve.

In Merchak et al’s research on Cranial Nerves , they mention that the abducens nerve divides into fibers that provide innervation to the lateral rectus muscle of the eye, which allows abduction of the eye when it is stimulated.

Facial nerve

In the investigation of the Department of Anatomy of the School of Medicine of the Catholic University of Chile on the Cranial Nerves , they define that this nerve is composed of motor and sensitive fibers that originate in three nuclear groups:

  • Main motor core
  • Parasympathetic nuclei: superior salivary and lacrimal
  • Sensitive core.

It has a complex and wide range of functions, since it mobilizes the muscles of the face and participates in the taste sensation of the tongue and some parts of the external ear, as well as regulating tear and salivary secretion.

Statoacoustic nerve

It is the eighth (VIII) of the twelve (XII) nerves. The general function of this nerve is to carry sensory information from the inner ear to theCnstag. Its fibers are then distributed to various regions of the inner ear.

Anatomically it is made up of two branches: the cochlear branch, which is in charge of hearing, and the vestibular branch, which is in charge of the sense of balance in the body.

The cochlear branch is the one that collects the sound and conducts it through the auditory canal. The vestibular branch, for its part, collects the movements for conjugated control of them, facilitating the posture.

Glossopharyngeal nerve

Thanks to this nerve, the gag reflex and the elevation of the soft palate are produced in our body. Prevents aspiration of solid or liquid material through the respiratory tract.

It is also composed of motor and sensory fibers. It is also responsible for the sense of taste in the posterior third of the tongue.

Pneumogastric Nerve

Also known as the vagus nerve, it has a series of components and connections that are very similar. It is a mixed nerve of motor and sensitive nature.

In addition to that, the pneumogastric nerve has that specific name because it innervates the organs of the digestive, circulatory, and respiratory systems, in addition to its functions in the head.

spinal nerve

It is also known as the accessory nerve, which consists of a cranial root and a spinal root. The cranial part is the smallest and receives connections from both cerebral hemispheres through corticonuclear fibers.

The spinal root is responsible for receiving connections from both cerebral hemispheres through corticonuclear fibers.

It is responsible for controlling the movements of the neck and shoulders, and to assess its correct functionality, the muscles are assessed to rule out atrophies and both sides of the trapezius muscles are compared.

hypoglossal nerve

The hypoglossal nerve controls the motor function of the tongue. It is located in the floor of the fourth ventricle and emerges from the skull through the hypoglossal canal.

For the evaluation and evaluation of this nerve, attention must be paid to the articulation of the patient’s words and atrophies or deviations are ruled out with an examination of the muscle.

Disorders and diseases associated with the cranial nerves

There are some triggers arranged in the cranial nerves, which can affect the health and functionality of the individual, which can be considered as disorders or diseases. They will be mentioned below.

cerebrovascular accident

Cerebrovascular accidents (ACV) occur in the area where the cranial nerves control facial movements, and it is for this very reason that in most cases this fluidity is affected or injured.

ACV are traumatisms, which lead to consequences of alterations in the cranial nerves. In fact, in the research titledCerebrovascular disease , emphasis is placed on the fact that the symptoms that cross over in this type of pathology affect these elements of our PNS.

Internuclear ophthalmoplegia

This pathology is described by the MSD Manual as a paralysis that prevents the signal from the VI cranial nerve from reaching the III nerve, resulting in a horizontal gaze with motor complications for the mobilization of the eyeball.

It is, in general terms, a condition between the connection of these cranial nerves.

Bell’s palsy

It is a disorder that affects the nerve that controls movement of the facial muscles. It is the VII cranial nerve and is usually idiopathic, that is, without apparent reason. It is benign and temporary. In many cases it can be the result of trauma, compression or tumor.

In the Bell’s PalsyResearch Study, they mention all the possible disorders to develop in conjunction with this pathology and that 90% of patients after treatment are able to fully recover.

Hemifacial Spasm

It is an involuntary contraction of one side of the face, which is considered a disorder due to nerve compression. They can start out intermittent and become more and more constant. Cranial nerves VII and VIII are involved.

Herpes zoster


It happens that in patients with diabetes mellitus, which is not dependent on insulin, mononeuropathies occur in the III, IV and V cranial nerve. It is one of the most common cranial disorders in individuals with these pathologies. In many cases ocular paralysis occurs, and blood flow is compromised.

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