A Better Understanding Of Cranial Nerve Diseases
What Are Cranial Nerves?
There are twelve cranial nerves that branch out from the brain to supply the structures in the face, head, neck, and abdominal organs. Disorders of the cranial nerves can manifest with different symptoms as each nerve can have various organs and muscles that it supplies. The twelve cranial nerves can have either sensory or motor innervations to the parts of the body.
Functions Of The Cranial Nerves
Cranial nerve number I is the olfactory nerve, and it is responsible for the sense of smell, while cranial nerve II is the optic nerve and it associated with the structures that produce sight and vision. Cranial nerves III, IV, and VI, are respectively called the oculomotor, trochlear, and abducens nerves. These nerves supply the muscles that move the eyeball. They help the person to see in different directions.
Cranial nerve V is the trigeminal nerve and it mainly deals with the sensory innervations to the face, and motor innervations to the muscles of the jaw. It helps move the jaws to breakdown food. Cranial nerve VII is the facial nerve and this is the nerve that supplies the innervations to the facial muscles. This allows us to frown, smile, or produce other facial expressions. It is also involved in the sense of hearing, taste, and producing saliva and tears.
Cranial nerve VIII is the vestibulo-cochlear nerve and it supplies innervations to parts of the ear. It is mainly responsible for hearing and balance. Cranial nerve IX is the glosso-pharyngeal nerve and it supplies taste sensation to the tongue, along with salivary gland secretion. The tenth cranial nerve (X) is the vagus nerve and this is responsible for innervating at least 90% of the organs in the thorax and abdomen. The accessory nerve is cranial nerve XI and it supplies the muscles that move the head and shoulders. Cranial nerve XII is the hypoglossal nerve and this is involved in innervating the tongue.
Testing For Cranial Nerve Diseases
If your doctor suspects you might have one of the various cranial nerve diseases, they will perform a series of sensory and motor tests to observe the functions of the structure the cranial nerve innervates. Therefore a person’s symptoms in cranial nerve diseases will depend on which cranial nerve is affected.
Examples of Cranial Nerve Tests
There are various cranial nerve tests to be administered. Examples of cranial nerve testing would be:
1.Testing cranial nerve I optic nerve by getting the person to read an eye chart.
2. Testing cranial nerve IV trochlear nerve by checking that the eyeball can move down and look inward.
3. Cranial nerve VIII function can be observed by using a tuning fork near the ear to test the hearing.
4. One of the ways cranial nerve X can be tested is by lightly placing a tongue depressor at the back of the throat to check the person’s gag reflex.
5. Lastly, cranial nerve XI can be tested by having the person carry out specific movements of the neck and shoulders.
References
Print Source: Cotran R, Kumar V, and Robbins, SL. 1999. Robbins Pathologic Basis of Disease, 6th Ed. W.B. Saunders Company, Philadelphia.
Web Source: Merck Manual Online. “Cranial Nerve Disorders.” 2007. Available: https://www.merck.com/mmhe/sec06/ch096/ch096a.html