Cranial pairs: 12 nerves coming out of the brain

Cranial pairs are a collection of nerves that protrude directly from the brain, Unlike the rest of the nerves of the nervous system.

In this article we will see what they are and what characterizes them, what is their location and exactly what functions they have in the human body.

What are cranial pairs?

In general, it can be said that the human brain communicates with almost all the nerves in the brain via the spinal cord.

So, for example, the information that comes to us about what we touch with our hands is collected by nerves that pass through the arm to reach the spinal cord, and from there to the brain, where it will be emitted. The object. This efferent order will also leave the brain via the spinal cord, and will reach the corresponding arm via the nerve fibers which exit from it.

However, this is not a rule that is always followed, as some nerves exit directly from the brain and do not originate in the spinal cord. These are the cranial pairs, or cranial nerves, Which originate from the lower part of the brain and reach their target areas through small holes distributed over the base of the skull. From these orifices, the cranial pairs communicate with the peripheral areas.

Also, although it may sound strange, not all of these cranial nerves are intended to reach the areas and organs in the head. Some extend to the neck and even the abdomen area.

How are cranial pairs classified and distributed?

The cranial pairs they are so called because they are counted in pairs, having both on the right side and on the left side of the brain. Thus, there are twelve cranial nerves pointing to the right hemisphere and twelve more pointing to the left, symmetrically.

Each pair is numbered with a Roman numeral depending on whether the position from which they come out of the brain is more or less close to the frontal area. In reality, cranial nerves can be grouped and categorized according to two criteria: The place from which they start and their function.

Cranial pairs classified according to their position

  • Starting from the areas above the brainstem are the pairs I and II.
  • Starting from the midbrain (the upper part of the brainstem), there are the cranial pairs III and IV.
  • Starting from the Varolio bridge (or trunk-brain bridge), there are cranial nerves V, VI, VII and VIII.
  • Starting from the medulla oblongata (in the lower part of the brainstem) are the nerves IX, X, XI and XII.

Cranial pairs classified according to their function

  • sensitive: Pairs I, II and VIII.
  • Linked to eye movements (And its parts) and eyelids: cranial pairs III, IV and VI.
  • Linked to the activation of the neck and tongue muscles: Cranial pairs XI and XII.
  • Mixed cranial nerves: Pairs V, VII, IX and X.
  • parasympathetic fibers: Nerves III, VII, IX and X.

What are the cranial pairs?

Let’s find out below which are the cranial pairs one by one, and their main functions.

1. Olfactory nerve (cranial pair I)

As indicated by his name, this cranial nerve is specifically dedicated to the transmission of nervous information about what is detected by the sense of smell, And so is an afferent fiber. It is the shortest of the cranial pairs because its destination is very close to the area of ​​the brain where it originated.

2. Optic nerve (cranial pair II)

It is also part of the afferent fibers, and is responsible for transmitting visual information collected by the eye to the brain. It comes from the diencephalon.

3. Oculomotor nerves (cranial pair III)

Also known as the common ocular motor nerve, this cranial nerve commands commands to most of the muscles involved in eye movement, And causes dilation or contraction of the pupil.

4. Trochlear or pathetic nerve (IV cranial pair)

Like the oculomotor nerve, this cranial pair deals with eye movement. Specifically, it sends signals to the upper oblique muscle of the eye. The place where this pair of nerves originates from is the midbrain.

5. Trigeminal nerves (cranial pair V)

It is one of the mixed cranial pairs, because it has both motor and sensory functions. In its motor nerve facet, it controls the muscles responsible for performing chewing movements, while as a cranial sensory nerve, it collects tactile, proprioceptive and painful information in various areas of the face and mouth.

6. Abductor nerve (cranial pair VI)

This is another of the cranial pairs responsible for moving the eyes. More precisely, it is responsible for producing abduction, that is, the eye moves to the side opposite to where the nose is located.

7. Facial nerve (cranial pair VII)

It is one of the mixed cranial pairs. It is both responsible for sending commands to the facial muscles dedicated to creating facial expressions (Thus allowing to socialize and communicate properly) as in the lacrimal and salivary glands. It also collects taste data of the language.

8.vestibulocochlear nerve (nerve equal to 8)

It is one of the sensory cranial pairs, and collects information in the hearing area. More precisely, it receives data relating to what is already felt in the position in which we are in relation to the center of gravity, which allows us to maintain balance.

9. Glosopharyngeal nerves (IV cranial pair)

It is both a sensitive and a motor nerve and, as the name suggests, it influences both the tongue and the pharynx (the channel that connects the mouth with the stomach). It receives information from the taste buds of the tongue, but also controls both the parotid gland (salivary gland) and the muscles of the neck which facilitate the action of swallowing.

10. Vagus nerve (cranial pair X)

It’s a cranial hair provides commands to most pharyngeal and laryngeal musclesIt sends the nerve fibers from the sympathetic system to the viscera which are found in the area of ​​our abdomen and receives taste information from the epiglottis. Like the glossopharyngeal nerve, it is involved in the action of swallowing, so it is very relevant given the importance of this vital function.

11. Accessory nerves (cranial pair XI)

To this cranial pair too it is known as the spinal nerve.

It is one of the pure cranial pairs, and activates the trapezius and sternoclidomastoid muscles, Which are involved in the movement of the head and shoulders, so that their signals are noticed in part of the upper chest region. Specifically, it allows the head to be tilted to one side and can be tilted back.

12. Hypoglossal nerve (cranial pair XII)

Like the vagus nerve and the glossopharynx, activates the muscles of the tongue and participates in the swallowing action. Thus, it works alongside the IX and X cranial pairs to allow correct swallowing, which is fundamental for the good condition of the body.

Bibliographical references:

  • Cardinali, DP (2000). Manual of neurophysiology. Madrid: Editions Diaz de Santos.
  • CHRISMAN, C., Morales, M. (2003). Handbook of practical neurology. Multimedia.
  • Davis, MC, Griessenauer, CJ, Bosmia, AN; Tubbs, RS, Shoja, MM “The Naming of the Cranial Nerves: A Historical Review.” Clinical anatomy. 27 (1): pages 14 to 19.
  • Müller, F and O’Rahilly R (2004). “Olfactory Structures in Staged Human Embryos.” Ellsrgans of cellular tissues (print) 178 (2): pp. 93-116.
  • Purves, D. (2011). Neurosciences. Sunderland: Sinauer.
  • Snell, RS (2003). Clinical neuroanatomy. Mexico: Pan American.

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