CRANIAL NERVES: REAL AND APPARENT ORIGIN, FUNCTIONS, ANATOMY - NEUROPSYCHOLOGY - 2025

The cranial nerves are twelve pairs of nerves that directly connect the brain and brainstem with different parts of the body such as muscles, organs and senses, transmitting essential information to carry out all kinds of vital functions in the human body.

Also known as cranial nerves, they are distributed through openings at the base of the skull in the head, chest, abdomen and neck. The part where they leave or enter the brain is known as apparent origin, but they all have a "real origin", different depending on the function they fulfill.

What differentiates the twelve cranial nerves from the rest of the nerves that leave the brain is that they do not join them through the spinal cord. On the contrary, they connect directly with the organs and muscles in whose operation they are involved, which are mainly located in the head.

There are many classifications for them, but the most used are those that divide them according to their function. In this sense, we usually speak of three types: sensitive, motor or mixed. They can also be classified according to whether they are afferent (they carry information to the brain) or efferent (they transmit it from the brain to the organs).

Each of the cranial nerves can be named with a number, or with a scientific name.

Below you will find a list of the technical names of the twelve cranial nerves, as well as a brief description of the functions they fulfill in the human body. You will also learn more about their real and apparent origin, and the parts of the anatomy in which they are found.

1- Olfactory Nerve (I)

The olfactory nerve, as its name suggests, has its real origin in the organs responsible for the sense of smell. Its mission is to transmit the information collected by them to the brain, where it is interpreted to generate an adequate response.

Real and apparent origin

The real origin of the olfactory nerve is located in a part of the olfactory mucosa known as the yellow spot; specifically, in the bipolar cells of the same, from where the components of the olfactory nerve come out. This area is at the top of the nostrils.

On the contrary, its apparent origin is the inner part of the olfactory bulb. This area of ​​the body is located on a part known as the ethmoid, above the cribriform plate.

Travel

The nerve fibers that arise from the bipolar cells of the yellow spot disperse in various directions, and then re-concentrate in the so-called olfactory branches. These are a set of nerves (whose number varies between 12 and 20), which reach the lower part of the olfactory bulb after crossing the cribriform plate of the ethmoid.

Near the olfactory nerve there is also another pair of nerves, which although it does not belong to the twelve cranial nerves, is also important. These are the so-called "terminal nerves."

2- Optic Nerve (II)

This afferent nerve has its real origin in the eyes. Its objective is to transmit all the visual information from these to the brain, specifically to the areas responsible for visual processing.

Real and apparent origin

The optic nerve arises from ganglion cells present in the retina of the eye. The axons of these cells (responsible for capturing light) form the origin of this cranial pair when they meet and go towards the brain.

On the other hand, its apparent origin is in the optic chiasm, specifically in the anterior angle.

Travel

The optic nerve is about 4 centimeters long, on its way from the eye to the visual areas of the brain. Traditionally it is divided into four parts: the intraocular segment, the intraorbital, the intracanacular, and the intracranial.

All these segments of the optic nerve pass through different areas of the skull (such as the cribrifying area of ​​the eyes or the optic foramen at the base of the skull) on their way to transmit visual information to the brain.

3- Oculomotor Nerve or Common Ocular Motor (III)

The third cranial nerve is the first of the efferents, that is, the first of those that transmit information from the brain to the body.

In this case, it is responsible for controlling the movements of the eye muscles, such as the eyelids, the pupillary sphincter, or some of those that serve to change their position.

Real and apparent origin

The oculomotor nerve is a little different from the previous two, in the sense that its fibers arise from two different nuclei. Thus, part of them originate in the somatomotor nucleus (located in the cerebral peduncles), and the rest originate from the motor parasympathetic nucleus (also known as Edinger-Westphal nucleus).

On the other hand, its apparent origin is located in the depression of the common ocular motor, which is found on the inside of the cerebral peduncles.

Travel

After leaving the brain stem, this nerve is directed outward in an upward direction. It passes close to the posterior cerebral artery, and the superior cerebellar artery, before rising above the pathetic nerve. In its final part, it is divided into two terminal branches:

- The superior terminal branch controls the superior rectus muscle of the eye, and the elevation of the upper eyelid.

- The inferior, on the other hand, controls the internal rectum, the inferior, and the minor oblique.

4- Trochlear or Pathetic Nerve (IV)

Also related to the control of the movement of the eyes, this cranial nerve is in charge of managing the muscles that rotate them downwards or towards the nose. For example, the superior oblique muscle of the eye.

Real and apparent origin

Its real origin is also in the cerebral peduncle, just below one of the common ocular motor nerve. The fibers intersect with those coming from the opposite side just before emerging to the surface.

The apparent origin of the trochlear nerve, on the other hand, is located in the posterior part of the cerebral peduncles, in an area known as the Vieussens valve.

Travel

The pathetic nerve surrounds the cerebral peduncles on the sides and goes towards the area known as the cavernous sinus. When it passes through its outer wall, it is placed between the ophthalmic nerve and the common ocular motor. After passing through the outside of Zinn's ring, it ends up in the greater oblique muscle of the eyes, which it controls.

5- Trigeminal Nerve (V)

The fifth nerve has a dual function. On the one hand, it transmits information from the sensory organs located on the face to the brain for its subsequent interpretation and elaboration of a response.

On the other hand, the trigeminal nerve is also responsible for controlling the two main muscles related to chewing: the temporal and the masseter.

Real and apparent origin

This nerve, because it has a mixed function, also has two real origins. On the one hand, there is the sensitive one, whose fibers arise in the Gasser ganglion.

On the other hand, it has a motor origin, which comes from the main or masticator nucleus (in the annular protuberance), and the accessory nucleus (which is found in the midbrain, in the cerebral peduncles).

The apparent origin of pair five, on the other hand, arises from the annular protrusion on its anteroinferior aspect. It does so through two roots: an external and thick one in charge of the sensitive function, and an internal and thin one that has to do with the motor.

Travel

The two roots of this nerve go together towards the upper edge of the boulder, crossing it through the notch of Gruber. Later, the sensitive branch forms a triangular plexus that empties into the Ganglion of Gasser.

The motor root, on the other hand, slides under the sensitive root. Later it passes under another ganglion known as Glaeer's, to finally join the lower maxillary branch.

6- Abductor Nerve or External Ocular Motor (VI)

The abductor nerve (also known as the Abducens) is the last nerve related to the control of the muscles used to move the eyes. In this case, it connects with the lateral rectus muscle, responsible for rotating the eyeballs in the opposite direction to the nose.

Real and apparent origin

The abductor nerve has its real origin in the pons nucleus, which is located below the fourth ventricle, and which generates the so-called eminence teres. This nucleus is surrounded by the motor root of the facial nerve.

The apparent origin, on the other hand, is located in the bulboprotuberancial sulcus, surrounding the blind hole.

Travel

From its apparent origin, this nerve enters the cavernous sinus and runs through it to the internal carotid. It then passes through the ring of Zinn until it enters the orbit through the sphenoid cleft.

This pair does not have any collateral branches, but all of its fibers end in the external rectus muscle of the eye.

7- Facial Nerve (VII)

Another of the nerves with a mixed function, it is responsible for controlling the muscles involved in the creation of different facial expressions, and it also makes the salivary and lacrimal glands work.

On the other hand, it is also involved in the sense of taste, since it collects information from the previous two thirds of the language.

Real and apparent origin

The real origin is found in two different nuclei: the sensitive - sensory (originated in the geniculate ganglion), and the vegetative (located in two nuclei located behind the motor, in the so-called protuberance). In turn, the latter is divided into the lacrimomuconasal, and the superior salivary.

The apparent origin is in the bulbous bulbo sulcus, outside of pair six and in front of eight.

Travel

The two branches of the facial nerve exit the pons, crossing the cerebellopontine angle together with the eighth pair. Both are introduced into the internal auditory canal, at the bottom of which pair seven penetrates the fallopian aqueduct.

This is one of the most complex pairs, being generally divided into three segments: labyrinthine, tympanic and mastoid. At its end, a distinction is normally made between the temporofacial branch and the cervicofacial branch.

8- Statoacoustic or Vestibuloclear Nerve

Image source: slideshare.net

He is involved in collecting information from the sensory organs present within the auditory system: the ear and kinesthesia. This second sense is part of the group of inmates, and allows us to perceive information about factors such as gravity, movement or balance of our body.

Real and apparent origin

The actual origin of pair eight is in the Scarpa ganglion. Its dendrites connect with organs such as the utricle and the saccule, while the axons go to the brainstem, meeting their end in the vestibular nuclear complex.

The apparent origin is in the bulboprotuverancial sulcus, located outside the facial nerve in addition to the intermediate of Wrisberg.

Travel

Starting from the internal auditory canal, the nerve travels to the lateral bulboprotuberancial groove, where it relates to the facial nerve after passing through the cerebellopontine angle.

9- Glossopharyngeal Nerve (IX)

The ninth cranial nerve collects information from the part of the tongue that is not connected to the facial nerve. In addition, it also controls the functioning of the parotid glands, which are responsible for producing saliva.

On the other hand, it also activates and contracts two muscles related to food intake, the styloglossus muscle and the stylopharyngeus muscle.

Real and apparent origin

The actual origin of the ninth pair can be divided into three parts: motor, sensory - sensory, and vegetative.

- The motor origin is in the nucleus ambiguus, which is located in the medulla oblongata.

- The sensory - sensory origin can be located in the Ehrenritter ganglion and in the Andersch ganglion.

- Finally, the vegetative origin is in the floor of the fourth ventricle.

The apparent origin, on the other hand, is located in the posterior collateral sulcus of the medulla oblongata.

Travel

The nerve exits the skull through the posterior foramen, just behind the pneumogastric and spinal nerves. It is separated from them by the jugular ligament.

Later it descends due to the retro-styling behavior of the maxillopharyngeal space, until it reaches its end at the base of the tongue.

10- Vagus or Pneumogastric Nerve (X)

It is responsible for contracting all the muscles related to the movements of the pharynx, which have to do with functions such as swallowing, phonation, breathing and hearing. It also controls most movements of the larynx, except those that are regulated by pair VIII.

Real and apparent origin

Again, the par ten has several origins: the somatomayor, the somatosensitive, and the vegetative.

- The somatomayor origin is in the middle part of the ambiguous nucleus.

- The somatosentitive origin, on the other hand, is found in the jugular ganglion and in the plexiform.

- Finally, the vegetative origin is located in the visceromotor nucleus and in the viscerosensitive.

The apparent origin of pair ten, on the other hand, is in the posterior collateral groove of the bulb, above the spinal nerve.

Travel

Pair ten exits the skull through the posterior recessed foramen, then down the retro-style compartment of the maxillopharyngeal space.

In him, there is a difference between the right and left pneumogastric. The right pneumogastric passes in front of the right subclavian artery but behind the right bronchus. On the other hand, the left one goes down in front of the arch of the aorta but behind the left bronchus.

In the lower part of the mediastinum, the two nerves meet the esophagus, each on one side. In this way, both pneumogastrics cross the diaphragm through the esophageal hiatus.

Finally, the left branch ends in the anterior part of the stomach. The right part divides into two branches, each ending in a lunate ganglion.

11- Accessory nerve (XI)

It is responsible for controlling the muscles related to the movements of the head and shoulders. The most important of them are the trapezius, and the sternocleidomastoid.

Real and apparent origin

Pair eleven has its real origin in two nuclei: the bulbar and the medullary. On the other hand, its apparent origin is found in the collateral sulcus of the medulla oblongata, and through the posterior collateral sulcus of the medulla.

Travel

Pair eleven exits the skull through the posterior torn hole, accompanying the glossopharyngeal and vagus. When it is outside the skull, it divides into an internal and an external branch, each ending in different places on the neck.

12- Hypoglossal Nerve (XII)

The last of the cranial nerves is responsible for activating the muscles related to almost all the movements of the tongue, especially those that have to do with the articulation of sounds and words, and with swallowing.

Real and apparent origin

The last cranial nerve has its real origin in the somatomotor nucleus located in the medulla oblongata. The apparent, on the other hand, is in ten or eleven floors located in the preolivar groove, also of the bulb.

Travel

Pair twelve exits the skull through the anterior condyle foramen, and then descends through the retro-stylous compartment of the maxillopharyngeal space. At the end of this journey, it reaches the edge of the tongue, where it ends.

References

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2. "Cranial nerves or cranial nerves: What are they and what functions do they perform in the brain" in: Cognifit. Retrieved on: May 29, 2018 from Cognifit: blog.cognifit.com.
3. "The 12 cranial nerves (name and position)" in: Knowing is Practical. Retrieved on: May 29, 2018 from Knowing is Practical: saberespractico.com.
4. "Cranial nerves" in: Salud 180. Retrieved on: May 29, 2018 from Salud 180: salud180.com.
5. "Cranial nerves" in: Wikipedia. Retrieved on: May 29, 2018 from Wikipedia: es.wikipedia.org.