Like the human roads that facilitate movement from point to point initiating delivery, the nervous system consists of the central nervous system.
It is made of the brain and the spinal cord.
While the peripheral nervous system made of cranial, spinal and the peripheral nerves alongside their motor and sensory nerves.
There is a total of twelve pairs of cranial nerves emanating from the brain rather than the spinal cord.
Their core function is to relay information between the brain and another part of the body more so in areas around the head and the neck.
Some other cranial nerves regulate the activity of the muscles. Other cranial nerves form link to the heart and the lungs.
Types of cranial nerves
The nerves are named from the posterior end to the anterior end of the brain starting with the olfactory nerve to the twelfth cranial nerve, the hypoglossal.
They are also named depending on their function.
The olfactory cranial nerve
Top on the list is the olfactory cranial nerve. It has its origin on the olfactory mucosa.
It penetrates through the cribriform plate and makes its destination on the surface of the brain. It is the shortest of all and very special when it comes to the sense of smell.
Not only that, it has an advanced function of taste. Above all what makes it so special is that it is capable of regeneration when damaged.
It consists of olfactory receptor neurons that are responsible for transmitting smell as soon as they receive perception by the olfaction.
As we descend the list, the optic nerve at position two is responsible for relaying visual senses from the retina to the brain.
It originates from optic disk and runs through the optic chiasm, optic tract, lateral geniculate nucleus and rest at the superior colliculus at the vision center of the brain.
The optic nerve has over one million nerve fiber and is made up of ganglion cells.
As we close at number two and welcome the oculomotor at number three, it is important to note that although the optic nerve is part of the eye, it is primarily considered as part of the central nervous system.
The oculomotor is the third nerve cell of the cranial nerve cells.
Its origin is in the midbrain where it starts from the third nucleus located lateral to the cerebral aqueduct on the gray matter.
It passes through the tegmentum, red nucleus and emerges from the sulcus on the middle part of the cerebral peduncle.
The oculomotor consist of the general somatic afferent that stimulates the movement of the skeletal muscle of the superior medial and inferior rectus.
Besides, it has the general visceral efferent that gives preganglionic parasympathetic to the ciliary ganglion.
At number four we present the motor trochlear nerve.
Unique from the rest of the nerves, having the fewest number of axons, the greatest intracranial length and the only nerve that emerges from the rear part of the brain.
Above all, it is the only cranial nerve that stimulates a muscle on the opposite side from where it originates.
Just like the optic nerve, its primary function lies in the eyes. The role, this time, is not on the visual aspect of the eye but eye movement.
It stimulates the superior oblique thus turning the eye downward and lateral.
It move forward and enters the Dura matter between the free and attached cells of the tentorium cerebella.
It goes up to the cavernous sinus where it enters the orbit via the superior orbital fissure. It winds diagonally across the levator palpebrae and superior rectus muscle to stimulate the oblique muscle.
From the eye, we move to the mouth where we find the trigeminal nerve responsible for chewing and pain of the mouth and face.
At number five in the list, we find the largest and very involved nerve- the trigeminal.
It provides sensation to the face, mucous membranes and other parts of the head.
It emerges from the brain consisting of a significant sensory root and a smaller sensory root originating from the Pons.
It travels laterally to meet the semilunar ganglion in the Meckel cave.
The nerve has sensory organs that provide tactile and nociceptive afferents to the face and mouth.
The nerve also has the motor organs that help in mastication.
Responsible for turning the eye laterally, the abducens comes at number six.
It is a somatic afferent nerve that regulates the movement of a single muscle- the lateral rectus muscle of the eye.
From the brainstem, the nerve travels upward between the Pons and the clivus where it penetrates the Dura mater.
From here it enters the cavernous sinus where it goes through the internal carotid artery. It stops at the arbitral fissure where it stimulates the lateral rectus muscle of the eye causing the eye to move laterally.
The facial nerve is responsible of all of the facial expression we express through our face. The key to these feelings lies behind facial nerve.
It originates from the brainstem between the medulla and the Pons. It has the large motor root and the small sensory root. The two roots move through the internal acoustic meatus where they open in the temporal bone.
From here, the nerve exits the internal acoustic meatus and goes into the facial canal. Here the two roots fuse to create the facial nerve. Th nerve continues to form the geniculate ganglion that gives rise to the greater petrosal nerve.
The facial nerve then leaves the facial canal and turns to run through the anterior to the outer ear where it provides motor stimulation around the ear. The motor root then continues to the parotid gland that make five branches that are responsible for stimulating the muscles of the face depending on the environment outside the face.
To be able to oppose the force of gravity on earth and acquire balance that makes us run, walk upright, bend and sit, the vestibulocochlear at number eight claims the importance.
It is responsible for transmitting sound and equilibrium. It made mainly of the bipolar nerves that branch into the cochlea and the vestibular nerve.
The cochlear run all the way to the inner ear where it stimulates the inner hair cells that are responsible for activating afferent receptors to respond to pressure waves that reach the basilar membrane through sound.
The vestibular nerve goes through the vestibular system of the inner ear. The vestibular ganglion has the bipolar neurons that extend to form five sensory cells. Three of them are the cristae that have hair cells that activate the afferent receptors to respond to rotational acceleration.
The other two are the maculae that stimulate the afferent receptor to respond to acceleration.
At number nine on our list, we encounter the glossopharyngeal nerve that is responsible for taste and sensing carotid blood pressure.
It consists of the afferent sensory nerve and the efferent motor information. From the upper medulla, the nerve travels through the skull at the jugular foramen and rest in the mouth in the mucous glands.
Here it functions to receive sensory fiber from the tongue, carotid body, the tonsil and the middle ear.
The vagus is responsible for sensing the blood pressure of the aorta, slowing down heart rate and stimulating digestive organ tastes.
The vagus emerges from the medulla oblongata and runs through the jugular foremen and ends at the neck, chest, and abdomen where it stimulates the viscera.
Besides, the vagus has afferent nerves that relay information about the state of the body to the central nervous system.
The nerve provides the sternocleidomastoid and the trapezius muscles.
The two muscles are responsible for the movement of the head away from the side the sternocleidomastoid muscles contracts, elevation of the shoulder through the action of the trapezius and drawing the head back thus keeping the face upward by the trapezius muscle.
At number twelve the hypoglossal closes the list with its stunning function of controlling the tongue movement.
The nerve emerges from the hypoglossal nucleus in the medulla oblongata of the brain. It then travels through the posterior cranial fossa.
The nerve then exits the cranium through the hypoglossal canal.
From here the nerve receives a branch of the cervical plexus that generate fibres from C1 AND C2.it then crosses the internal and external carotid arteries and terminating in the anterior direction and enters the tongue.
Cranial Nerves Mnemonics –
Here are some useful mnemonics that will help you to easily remember the cranial nerves.