These nerves emerge from underneath the brain and transmit information between the brain and other parts of the body mostly in the head and neck region. Some of them relay information from the sensory organs to the brain, some control muscle movements and others connect to the internal organs like heart, lungs, etc. or glands.
There are totally 12 pairs of cranial nerves that are numbered and named according to their location ranging from the front to the back of the brain. Cranial nerves traverse through different paths within and outside the skull. The internal paths are called as intracranial and the external is called as Extra-Cranial.
The nerves exit the skull through small openings called foramina. There are generally paired and are present on both the left and right side of the body. Information can be passed on the same side or from one side to another to generate a particular function of the body.
Types of Cranial Nerves
They are typically named based on their structure or function they perform.
- Olfactory – It contributes to the sense of smell. It relays information from the nasal epithelium to the brain’s olfactory center.
- Optic – Sensory nerve that contributes to our vision. It supplies information to the retina by means of ganglion cells
- Oculomoter Nerve – It manages the movements of the eyelids, rotates eyeballs and dilation of the pupil when exposed to light. Basically, it monitors the muscles of the eye.
- Trochlear – It handles the muscle movements of the eye and the function of turning the eye.
- Trigeminal – It is the largest cranial nerve with various functions. It handles the sensory functions of nose, eyes, tongue and teeth and is further narrowed down to three categories of branches namely ophthalmic, maxillary, mandibular nerves. All together, they also provide stimulation to the skin of the face and control the process of muscles when chewing.
- Abducent – This is again part of the eye functioning by controlling certain movements of the eye and enables to turn the eye laterally.
- Facial – It controls our facial expressions and resides on the stem of the brain. Supplies sensory information of the touch sensation on the face and controls the tongue as well.
- Vestibulocochlear – It resides near the inner ear and comprises of the vestibular nerve that maintains the balance of the head and cochlear functions enabling to hear the sound from our ear.
- Glossopharyngeal – It is a sensory nerve that takes care of the throat or pharynx and certain functions of the tongue and palate. It relays information about temperature, pressure, etc. and aids swallowing of food.
- Vagus – It carries out both sensory and motor functions. It controls the muscle movements of the pharynx, trachea, esophagus and parts of heart and palate. It also controls the sensory ability of taste function of the tongue.
- Spinal Accessory Nerve – Going by its names, it takes care of information communicated about the spinal cord and other surrounding muscles. It controls the muscle movement of the shoulder and neck around it.
- Hypoglossal Nerve – It monitors the movement of the tongue and takes care of the muscles of the tongue.
Cranial Nerve Disorders
As seen the cranial nerves contributes to the sensory or motor innervations that include the function of vision, hearing, taste, smell, balance, touch and temperature. A deficiency of any of the above cranial nerves leads to disorders or adverse conditions of the particular function that is related to the nerve.
The disorder can include injury, inflammation, tumor, infections, toxins and improper blood supply. Some of the prominent disorders that can occur are following:
- Optic Nerve Disorders – It can cause problems in the vision and can cause blindness at times
- Hemifacial Spasm – It causes a twitching movement on one side of the face that is often incurable. It usually starts with the eye and then eventually progresses to the cheek and mouth. There is no pain involved and an involuntary movement with no specific oral medicines to treat it.
- Trigeminal Neuralgia – It is characterized by a shooting pain in the face and is caused due to the pressing of the nerve on the lower part of the brain. The pressing of the nerve can have multiple originations including brain tumor or multiple sclerosis for which an MRI scan is advised to determine the cause. It can be treated with oral medications.
- Glossopharyngeal Neuralgia – Similar to the above disorder, pain occurs in the throat or tonsil region due to swallowing or involuntarily.
- Meniere’s disease – It is a hearing disorder that involves fluctuations in hearing, pressure in the ear or dizziness. Medicines prescribed for this condition can be taken to alleviate the dizziness or hearing problem
- Vertigo – The full form of this disorder is Benign Paroxysmal Positional Vertigo. It is not a very serious problem and thus the name benign. It happens all of a sudden with a change in the position of the head causing a whirling or dizzy sensation. When tilting your head, looking up or down the patients may experience this and can also happen due to age factor.
- Stroke – A clot in the blood vessel can lead to damages to certain cranial nerves and cause specific symptoms of paralysis of certain functions
- Inflammation – It can deter the function of the particular cranial nerves due to certain infections. For example, a condition called Bell’s palsy occurs due to the inflammation of the facial nerve