Cranial nerves: the 12 nerves leaving the brain

What are the cranial nerves and what is their function in the central nervous system?

The cranial nerves are a set of nerves that come directly from the brain, unlike the other nerves of the nervous system.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 what exactly are their functions in the human body.

What are the cranial nerves?

Generally speaking, it can be said that the human brain communicates with almost all the nerves of the brain through the spinal cord.

Thus, for example, the information that reaches us about what we touch with our hands is picked up by nerves that travel through the arm until they reach the spinal cord, and from there to the brain, from where the order to continue examining the object will be issued. This efferent order will also leave the brain through the spinal cord, and will reach the corresponding arm through the nerve fibers that come out of it.

However, this is not a rule that is always fulfilled, since there are also some nerves that come directly from the brain, without being born in the spinal cord. These are the cranial nerves, or cranial nerves, which arise from the lower part of the spinal cord.They arise from the lower part of the brain and reach their destination areas through small holes at the base of the skull. From these holes, the cranial nerves communicate with peripheral areas.

In addition, although it may seem strange, not all of these cranial nerves have the function of reaching areas and organs located in the head. Some extend to the neck and even the abdominal area.

How are the cranial nerves classified and distributed?

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

Each pair is numbered with a Roman numeral according to whether the position from which they exit the brain is more or less close to the frontal area. In fact, the cranial nerves can be grouped and classified into categories according to two criteriaThe place from which they originate and their function.

Cranial nerves classified according to their position

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

Cranial nerves classified according to their function

• SensorySensory: pairs I, II and VIII.
• Related to the movements of the eyes (and their parts) and eyelids. (and their parts) and eyelids: cranial nerves III, IV and VI.
• Related to the activation of neck and tongue muscles: cranial nerves XI and XI.cranial nerves XI and XII.
• Mixed cranial nervesmixed cranial nerves: cranial nerves V, VII, IX and X.
• Parasympathetic fibersparasympathetic fibers: nerves III, VII, IX and X.

What are the cranial nerves?

We are going to know hereafter what are the cranial nerves one by one, and their main functions.

1. Olfactory nerve (cranial nerve I)

As its name indicates, this cranial nerve is specifically dedicated to transmit nervous information about what is detected through the sense of smell, and therefore it is a fiber of the olfactory nerve.and is therefore an afferent fiber. It is the shortest of the cranial nerves, since its destination is very close to the area of the brain from which it arises.

2. Optic nerve (cranial nerve II)

It is also part of the afferent fibers, and it is is in charge of transmitting to the brain the visual information that is collected from the eye.. It arises from the diencephalon.

3. Oculomotor nerve (cranial nerve III)

Also known as the common ocular motor nervethis cranial nerve sends commands to most of the muscles involved in eye movement, and causes the pupil to dilate.and causes the pupil to dilate or contract.

4. Trochlear nerve, or pathetic (cranial nerve IV)

Like the oculomotor nerve, this cranial nerve is involved in eye movement. is concerned with eye movement. Specifically, it sends signals to the superior oblique Muscle of the eye. The place from which this nerve pair arises is the midbrain.

5. Trigeminal nerve (cranial nerve V)

This is one of the mixed cranial nerves, because has both motor and sensory functions. As a motor nerve, it sends commands to muscles responsible for chewing movements, while as a sensory cranial nerve it collects tactile, proprioceptive and pain information from various areas of the face and mouth.

6. Abducens nerve (cranial nerve VI)

This is another of the cranial nerves responsible for causing the eye to move.. Specifically, it is responsible for producing abduction, that is, the eye moves to the side opposite to where the nose is.

7. Facial nerve (cranial nerve VII)

It is one of the mixed cranial nerves. It is in charge of sending orders to muscles of the face dedicated to create facial expressions (thus allowing to socialize and communicate correctly). (thus allowing us to socialize and communicate correctly) as well as to the lacrimal and salivary glands. It also collects taste data from the tongue.

8. Vestibulocochlear Nerve (cranial nerve VIII)

It is one of the sensory cranial nerves, and it collects information from the auditory area. Specifically, it receives data relating to what is heard and the position in which we are in relation to the center of gravity, which allows us to maintain our balance.

9. Glossopharyngeal nerve (cranial nerve IV)

It is both a sensory and motor nerve and, as its name indicates, it influences both the tongue and the pharynx (the duct that communicates the mouth with the stomach). It receives information from the taste buds of the tongue, but also sends commands to both the parotid (salivary) gland and neck muscles that facilitate swallowing.

10. Vagus nerve (cranial nerve X)

This cranial nerve carries commands to most of the pharyngeal and laryngeal muscles, sends nerve fibers from the laryngeal system to the pharynx and larynx.It sends nerve fibers of the sympathetic system to viscera found in the area of our abdomen and receives gustatory information coming 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 nerve (cranial nerve XI)

This cranial nerve is also known as the is also known as spinal nerve.

It is one of the pure cranial nerves, and it activates the trapezius activates the trapezius and sternocleidomastoid muscles, which are involved in the movement of the spine.It activates the trapezius and sternocleidomastoid muscles, which are involved in the movement of the head and shoulders, so that its signals are felt in part of the upper thorax. In particular, it allows the head to be tilted to one side and to tilt backwards.

12. Hypoglossal nerve (cranial nerve XII)

Like the vagus nerve and the glossopharyngeal nerve, activates muscles of the tongue and participates in the action of swallowing.. Thus, it works together with cranial nerves IX and X to allow swallowing to be performed correctly, which is essential for the good condition of the organism.

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