12 Cranial Nerves – Cranial nerves or also called Cranial Nerves in Latin are 12 pairs of nerves that exist in humans and stick out directly from the human brain. The 12 cranial nerves are different from the prominent spinal nerves in the human spine. Pairs of cranial nerves are marked by numbers according to the position of the nerves from front to back.
The 12 cranial nerves are part of the peripheral nervous system arrangement which are attached to the central nervous system or SPP. These nerves are primarily connected to the structures of the human head and neck, such as the nose, eyes, ears, mouth and tongue. So that the 12 cranial nerves can regulate the abilities of the five human senses such as hearing, sight, smell and also expression.
To find out more about the 12 cranial nerves, see the explanation to the end in this article!
Definition of 12 Cranial Nerves
According to a study published in 2019 in the journal Insight into Imaging, the human body is known to have 12 cranial nerves that function to control motor and sensory functions in the head and neck.
The anatomy of the 12 cranial nerves is quite complex and their dysfunction can be caused by tumors, infections or traumatic injuries. To get a complete imaging picture of the 12 cranial nerves, Sinaumed’s can use Magnetic Resonance Imaging or MRI and Computed Tomography or CT procedures.
The human brain consists of 12 cranial nerves that have names according to their function and structure. These nerves will help a person to taste, hear, smell, see and other abilities.
Even these 12 cranial nerves can also help a person to make facial expressions such as winking, moving the tongue or smiling.
What Are the 12 Cranial Nerves?
Each part of the 12 cranial nerves has a roman numeral from I to XII. the numbering of the 12 cranial nerves has been adjusted according to the location of these nerves which are from the front to the back of the brain.
The function of each nerve is to regulate sensory function as well as motor function. Sensory nerves have a relationship with the senses, for example the sense of hearing, the sense of smell and touch.
Then the motor nerves function to control movement and function of muscles and glands. The following are the types of cranial nerves and the function of each nerve.
1. Olfactory nerves
The first part of the cranial nerve is the olfactory nerve. The olfactory nerve can send sensory information to the brain related to odors entering through the nose.
When a person inhales aromatic molecules, the odor enters the olfactory epithelium. This can stimulate receptors that generate nerve impulses in the olfactory department. Then, signals will be sent to the brain related to memory and smell recognition.
2. Optic nerve
The second cranial nerve associated with vision is the optic nerve. Light will enter the eye and come into contact with the receptor. Information received by these receptors will be transmitted from the retina to the optic nerve.
Then, impulses from the optic nerve will reach the visual cortex which is capable of processing information related to vision. The visual cortex is located at the back of the brain.
3. Oculomotor nerve
The third nerve from the cranial nerves is the oculomotor nerve which can help control the movement of the eye muscles. This third nerve is at the front of the midbrain and part of the brainstem.
The oculomotor nerve has two distinct motor functions, such as muscle function and pupillary response. The following is an explanation of its functions.
- The muscle function of the oculomotor nerve can provide motor function to four of the six muscles around the eye. This muscle will help the eye to be able to move and focus on the object it sees.
- Pupillary response is the part that can help to control the size of the pupil that responds to light.
4. Trochlear nerve
The fourth of the 12 cranial nerves is the nerve that controls the superior oblique muscle, whose function is to move the eye. The trochlear nerve is the same as the oculomotor nerve, but the trochlear nerve originates from the back of the brain.
With the fourth nerve, the strength of the oblique muscle will make the eye able to see in the desired direction.
5. Trigeminal nerve
The fifth nerve of the cranial nerve is the largest nerve compared to the other nerves. The trigeminal nerve has sensory functions as well as motor functions. The motor function of the trigeminal nerve is to help chew and clench teeth.
This nerve has three arrangements, which are as follows.
- Ophthalmic which functions to give sensation to various parts of the eye, including the mucosa in the nose, eyes including the cornea, eyelids to the forehead.
- The upper jaw is the part that functions to communicate sensory information to the central part of the face, for example the upper cheeks, upper teeth, lower eyelids and nasal cavities.
- The mandible is the part that can provide sensation to the lower third of the face, lower teeth and tongue.
The most common and prone disorder of the trigeminal nerve is trigeminal neuralgia. This problem can cause intense pain and facial tics on the face. Facial tics are sudden movements that occur repeatedly and occur on the face, neck or head.
6. Abducens nerve
The sixth nerve is the part of the cranial nerves that controls the lateral rectus muscle. The lateral rectus is part of the extraocular muscles or the main muscles that move the eyeball.
This muscle is involved in outward movement of the eye, such as when the eye moves sideways.
The abducens nerve begins in the pons of the brainstem, then enters an area called Dorello’s canal, then passes through the cavernous sinus to finally the lateral rectus muscle in the bony orbit.
7. Facial nerve
The facial nerve is part of 12 cranial nerves consisting of 4 nuclei with different functions, which are as follows.
- Muscle movements that function to produce facial expressions.
- Movement of the lacrimal, submandibular and submaxillary glands.
- Sensation in the outer ear
- Sensations related to taste.
One of the most common disorders of the facial nerve is Bell’s palsy. This disorder can cause paralysis on one side of the face and even loss of sensation.
8. Vestibulocochlear nerve
The eighth cranial nerve is related to one’s hearing and balance.
There are two components of the function of this eighth nerve, namely as follows.
- Can help the body to feel changes in the position of the head related to gravity in order to maintain balance.
- The cochlear nerve in this eighth nerve can help hearing. The hair cells in the ear will vibrate in response to sound and determine the frequency as well as the amount of sound.
9. Glossopharyngeal nerve
The glossopharyngeal nerve is the fifth nerve which has a function related to the sense of taste and a person’s ability to swallow. Some of the motor as well as sensory functions of this nerve include the following.
- Transmits sensory information from the sinuses to the back of the throat, the inner ear and the back of the tongue.
- Gives taste to the back of the tongue.
- Stimulates the movement of a muscle at the back of the throat called the stylopharyngeus.
The ninth nerve is located in a part of the brainstem called the medulla oblongata. This section can also extend to the neck and throat area.
10. Vagus nerve
The tenth nerve section of the cranial nerves has sensory functions as well as motor functions, such as:
- Able to communicate sensational information from the ear canal as well as parts of the throat.
- Able to transmit sensory information from organs such as the chest and trunk, such as the heart and intestines.
- Allows to control the motor muscles in the throat.
- Stimulates the muscles of the organs in the chest and trunk, including those that move food through the digestive tract or peristalsis.
- Gives a close taste to the root of the tongue.
Of the 12 cranial nerves, the vagus nerve has the longest pathway. This nerve extends from the head in a part of the brainstem called the medulla to the abdomen.
11. Accessory nerve
Accessory nerves are part of the cranial nerves that control the muscles in the neck. This muscle is capable of flexing, rotating and extending the neck and shoulders.
The accessory nerve is divided into two parts, namely the spine and the skull. The two parts of the accessory nerve briefly touch before part of the spinal nerve moves to supply the muscles in the neck, meanwhile, the cranial part follows the vagus nerve.
12. Hypoglossal nerve
The last cranial nerve is the hypoglossal nerve which functions to move most of the tongue muscles. This section starts from the medulla oblongata then moves down to the jaw until it reaches the tongue.
If the hypoglasic nerve is disturbed, paralysis of the tongue can occur and most often occurs on one side.
That’s 12 types of cranial nerves. When read carefully, it can be seen that the cranial nerves are nerves that are located near the brain and are divided into 12 pairs of nerves. The 12 nerves pass through the cranium, so these nerves are called cranial nerves.
Cranial Nerve Function
The cranial nerves are named according to the order from top to bottom and the main function of the cranial nerves is to regulate all the functions of the organs in the head. From awareness, communication function, chewing function to swallowing function.
In general, the function of the cranial nerves can be divided into three types of functions, namely sensory, motor and autonomic. One of the functions of the cranial nerves is to allow a person to swallow as well as speak.
1. Swallow
When a person chews or drinks, the food and drink will pass posteriorly from the tongue, the muscles innervated by the Vagus or X nerve and the glasopharyngeal (IX) will push the food down and back towards the hypopharynx, then through the cricopharyngeal sphincter to the esophagus.
The nasopharynx is covered by palatal muscles which are innervated by the fine and trigeminal nerves. While the eustachian tube will open. The laryngeal orifice narrows with elevation of all the laryngeal bones by all the muscles attached to the bones from above and the opening of the cricopharyngeal sphincter. The tongue muscles which are innervated by the hypoglossal nerve (XII) also have an important role in this process. Most of the pharyngeal muscles are innervated unidirectionally via the vagus nerve.
2. Speak
The process of real speech goes through various processes so that a complete sentence is formed. There are three speech processes, here are the explanations.
a. Production of sound through a phonation
During phonation, the vocal cords create a narrow slit which allows air to pass directly through to produce sounds such as those of a flute or an organ pipe. The muscles that move the vocal cords are innervated by the recurrent laryngeal nerve which is part of the vagus nerve.
b. Making understandable sounds through an articulation
The pharyngeal muscles (X) of the tongue, facial excretory muscles, mandibular and palatal movements all have a role to make meaningless sounds more understandable.
c. pitches
Pitch is modulated by contracting the cricothyroid muscle and relaxing the vocal cords. All movements of the vocal cords are controlled by the nucleus ambiguus via the superior and recurrent laryngeal nerves. Lesions in this nucleus can lead to swallowing and speech abnormalities commonly referred to as bulbar and pseudobulbar palsy.
12 cranial nerves can be examined in several ways, for example the olfactory nerve can be examined by closing the patient’s eyes, then the patient is asked to distinguish between several odors. While the optic nerve can be examined through the snelend card and check the eyesight.
The oculomotor nerve can be examined by rolling the eyeball, moving the conjunctiva, pupil reflex and inspecting the eyelids. The trochlear nerve can be examined by rolling the eyeball, moving the conjunctiva.
The trigeminal nerve can be examined by moving the patient’s jaw throughout the jaw area or by closing the eyes or touching the forehead or cheek with cotton.
The abducens nerve can be examined by rolling the eyeball, pupil reflex and inspecting the eyelids. The facial nerve can be examined by smiling, raising eyebrows and so on. The verstibulocochlear nerve can be examined with the Weber or Rinne test.
The glossopharyngeal nerve can be differentiated by distinguishing sour and sweet tastes, the vagus nerve can be examined by touching the posterior pharynx, the accessory nerve is examined by moving the shoulder, finally the hypoglossal nerve can be tested by sticking out the tongue and moving the entire mouth area.
That’s a review of the 12 cranial nerves along with their functions and how to do the test. Sinaumed’s can find out more about nerves or other parts of the body by reading books available at sinaumedia.com . sinaumedia always provides useful and original books so that Sinaumed’s has #MoreWithReading information.
Author: Khansa