Cranial nerves
Cranial nerves are the nerves that emerge directly from the brain. 10 of the 12 cranial nerves originate in the brainstem. The main responsibility of the cranial nerves is to relay information between the brain and parts of the body. This basically happens from the head and the neck regions. The 12 pairs of cranial nerves are responsible for human daily performance in a comfortable and efficient way. They also take part in the information of our senses to the brain.
Check out this small guide that shares about the cranial nerves, their anatomy, their classification and their faction in our bodies. The 12 pairs of cranial nerves pass through some small holes at the base of the human skull.
The main responsibility of the nerves is to carry the information and connect the brain to the different parts of the body such as sensory organs, muscles, organs among other body parts. Throughout all this time, the human brain does not rest and there is a continuous communication with almost all the brain nerves through the spinal cord.
Do you notice while you step your feet on a soft object? You are able to do this through the signal transmitted through the leg nerves going all the way to the spinal cord, then to the brain. Since what you are stepping on is soft or friendly to your body, then the brain gives the order of continuous stepping of that pleasant object.
This order will descend back and reach the feet just like the way it went up to the brain. Cranial nerves are unique because they emerge directly from the brain without passing via the spinal cord. This is due to their location which is the lower part of the brain. They go through the holes at the base of the skull for them to reach their destination. These nerves are also directed to other areas of the body such as the neck and the thoracic area as well.
That is how the cranial nerves are seen as part of the nervous system. Basically, they are part of the peripheral nervous system. The same nervous system is the one that relates the brain to the cranial and cervical structures. All this is done in an afferent direction, sensory, sensorial, motor and vegetative in an efferent direction. There are 12 cranial nerves on each side of the left and right hemisphere. Each of these cranial nerves is all in paired mode. The function and the emergence of the cranial nerves are what determine their order of numbering.
List of cranial nerves
The cranial nerves have an association with roman numerals and the numbers range from 1 to 12. The cranial nerves emerge as above the brain stem, there is a pair I and II. From the midbrain are pair III and IV from the varolius bridge are the cranial nerves V, VI, VII and VIII. From the medulla oblongata, there are the cranial pairs IX, X, XI, and XII.
The functions of the 12 cranial nerves
It is very important to note that every cranial nerve has its specific functions. They are listed and arranged according to the corresponding roman numbers assigned to the cranial nerve. Find out what function each cranial pair has on your body below:
I – Olfactory Nerve
This is the first cranial nerve in the list. It is actually the sensory nerve in charge of transmitting olfactory stimuli from the nose to the brain and it is also in charge of the smell. Another unique feature about it is that it’s the shortest cranial nerve and its actual origin is given by the cells of the olfactory bulb.
The aromatic molecules you inhale dissolve in a moist lining at the roof of your nasal cavity. This place is called the olfactory epithelium. The olfactory bulb is an oval-shaped structure containing specialized groups of nerve cells.
II – Optic Nerve
It is the second cranial pair among the 12 pairs of cranial nerves. Its main responsibility is to conduct the visual stimuli from the eye to the brain thus making it in charge of vision. It is made of axous from the ganglion cells of the retina and it emerges in the diencephalon. The information taken to the photoreceptors to the brain is later integrated and interpreted.
The light that enters your eyes comes into contact with special receptors in the retina called nods and cons. Rods are highly sensitive to the light and are found in large numbers. Cons on the other hands are found on similar numbers. They mostly get involved in color vision and they have lower light sensitivity compared to rods.
The information that is received from rods and cons is transmitted in the retina to the optic nerve. The optic nerves in your skull meet to form something called the chiasm and the nerve fibers from half of each retina form two optic tracts. The nerve impulses reach your visual cortex via each optic track and that is how the information is processed. The visual cortex is located at the back part of your brain.
III – Oculomotor Nerve
Oculomotor is a cranial nerve also referred to as the common ocular motor nerve. The third on the list of the 12 pairs of cranial nerves are responsible for controlling the eye movement and the size of the pupil as it responds to the light. Its origin is the midbrain.
IV – Trochlear Nerve
This is one nerve with two functions known as motor and somatic functions. These two functions are connected to the superior oblique muscle of the eye. This is why the eyeballs move and rotate accordingly. This fourth pair of the cranial nerves originates in the mesencephalon and the Oculomotor nerve. It is responsible for downward and inward eye movement. Just like your Oculomotor nerve, it moves forward and when it reaches the eye sockets, it stimulates the superior oblique muscle.
V – Trigeminal Nerve
It is the largest cranial nerve with a mixture of sensitive, sensory and motor nerves. It is the fifth of the 12 pairs of cranial nerves and its function is to carry sensitive information to the face to convey information of chewing process. The sensory fibers also convey sensations of touch, pain, and temperature. This is done from the head’s front including the mouth and the ménages. Thus, it is responsible for facial expression. The sensory root of the trigeminal nerve is the one that branches into the following three divisions:
a) Ophthalmic: The ophthalmic division is in charge of sending sensory information from the upper of the face. This includes your forehead, scalp and upper eyelids.
b) Maxillary: This one is responsible for communication with sensory information from the middle part of the face. This includes your cheeks, upper lid, and nasal cavity.
c) Mandibular: Mandibular division contains both the sensory and motor function. It is responsible for sending sensory information from the ears, lower lip, and chin. It is also in charge of controlling the movement of the muscles within your jaw and ear.
VI – Abducent Nerve
It is also referred to as the external ocular motor cranial nerve. It is a cranial motor pair and its responsibility is to transmit the motor stimuli to the external rectus muscles of the eye. This allows the eye to move to the opposite side from the nose. It is the sixth of the 12 pairs of cranial nerves.
It starts in the pons region of the human brainstem and eventually enters the eye socket. This is where it controls the lateral rectus muscle. It is involved in outward eye movement. For instance, if you are looking at the side, you are able to do that because you are using this muscle.
VII – Facial Nerve
This is also a mixed cranial pair and it consists of several nerve fibers which perform different functions. These functions include ordering the muscles of the face to create facial expressions in some muscles in the jaws and send signals to the salivary and lacrimal glands. It also collects taste information through the tongue. It also supplies glands in the head or neck area and a good example would be the salivary glands and tear-producing glands. It also helps to communicate sensations from the outer part of your ear.
It is the seventh of the 12 pairs of cranial nerves and originates in the pons area of the brainstem. Here, it has a motor and sensory root and the two nerve fuse together to form the facial nerve. The facial nerve provides sensory information by branching further into smaller nerve fibers within and outside the skull.
VIII – Vestibulo-Cochlear
It is also known as auditory and vestibular nerve. It is a sensory cranial nerve that forms the vestibulocochlear. It is responsibility is to balance and orient in space and auditory function. It is the eighth of the 12 pairs of cranial nerves and it consists of two parts known as:
a) Cochlear portion: there are specialized cells within your ear to detect vibrations from soundly based off the sound’s loudness and pitch. The nerve impulse generated is transmitted to the cochlear nerve.
b) Vestibular portion: there is another set of special cells here that can track linear and rotational movements of your head. The information transmitted to the vestibular nerve and used to adjust body balance and equilibrium is found here.
The origination of cochlear and vestibular portions of the vestibulocochlear nerve is the separate areas of the brain. The cochlear portion begins in the inferior cerebellar peduncle, an area in the human brain. The vestibular portion, on the other hand, begins in the pons and medulla and they both combine to form the vestibulocochlear nerve.
IX – Gloss-Pharyngeal Nerve
This is one nerve whose whole influence lies on the tongue and pharynx. This is because it collects information from the taste buds and sensory information from the pharynx. It also leads orders to the salivary gland and various neck muscles. These muscles help in swallowing. This is the ninth of the 12 pairs of cranial nerves and it helps in monitoring the blood pressure.
It is responsible for sending information from sinuses, back of the throat, some parts of the inner ear and back part of your tongue. It provides a sense of taste for the back part of the tongue, stimulates the voluntary movement of a muscle in the back of the throat known as the stylopharyngeus.
X – Vagus Nerve
This emerging nerve from the medulla oblongata is also known as pneumogastric and it has the longest pathway since it extends from the head to the abdomen. It supplies nerves to the pharynx, esophagus, larynx, trachea, bronchi, heart, stomach and liver. This nerve is also responsible for influencing the action of swallowing, sending and transmitting signals to the autonomous system. This helps to regulate the activation and control of body stress levels. It can also send a direct signal to the sympathetic system.
It is also in charge of communication sensation information from the ear canal and parts of the throat. It also sends sensory information from organs in the chest and trunk. A good example is a heart and the intestines. It also allows motor control of muscles in the throat and it is involved in the stimulation of the muscles of organs in the chest and trunk. It is responsible for providing a sense of taste near the root of the tongue. It is the tenth of the 12 pairs of cranial nerves.
XI – Accessory Nerve
It is named as the spinal nerve. It is a motor nerve and may be understood as one of the most ‘pure’ nerves. Its importance is to govern nerves movement of the head and shoulders. It does this by supplying the sternocleidomastoid and trapezius muscles in the anterior and posterior regions of the neck. This is also the nerve that is involved in governing movements of the head and shoulders. It does this by supplying the sternocleidomastoid and trapezius muscles in the anterior and posterior regions of the neck. It is also responsible for the head movement allowing you to throw your head back.
It is divided into two parts. The first part is the spinal portion that originates in the upper part of the spinal cord. The other part is cranial parts in the medulla oblongata. This is the second last of the 12 pairs of cranial nerves.
XII-Hypoglossal Nerve
This is the twelfth of the 12 pairs or cranial nerves. It is a motor nerve and is involved in the tongue muscles control, swallowing and speech just like the vagus and the gloss pharyngeal.
