There are a few topics that are known to give medical students nightmares. The structure and function of the cranial nerves is one of those topics. There are twelve cranial nerves. They are named this because they all begin in the brain itself. They have a wide variety of functions, mostly involving structures in and around the head.
There is nothing particularly interesting about the structure of the cranial nerves. They are regular nerves in just about every way. They begin in the brain and travel to the area of the body where they are used for sensory functions or movement (or both in some cases). The twelve cranial nerves each have a unique name, as well as a number.
Cranial Nerve I: Olfactory
The first cranial nerve is the olfactory nerve. This is the nerve that transmits smell information from your nose to the brain. The next time you smell the dog poop you are picking up in the park, you can thank the efficiency of the 1st cranial nerve for that lovely smell.
Cranial Nerve II: Optic
The second cranial nerve is the optic nerve. This nerve comes out of the brain and travels to your eye. It is involved only in the sensory aspect of vision. This is the nerve that allows you to see things. It doesn’t not move the eyes (that’s done by other cranial nerves).
Cranial Nerve III: Oculomotor
This nerve is responsible for controlling many (but not all) of the muscles around the eye. These muscles are used to move the eye in the eye socket. Without them, you wouldn’t be about to look around without moving your entire head. The specific muscles that are controlled by the 3rd cranial nerve include the inferior, medial, and superior rectus, inferior oblique, and the levator palpebrae superioris.
Cranial Nerve IV: Trochlear
This nerve has only one function. It controls a muscle in the eye called the superior oblique. Without this nerve, some of the movements of the eye are compromised.
Cranial Nerve V: Trigeminal
The 5th cranial nerve is a very important one. It has both sensory and motor functions in and around the face. It is responsible for all touch sensation on the face. In addition, it controls the muscles that are involved in chewing. There are three major branches of this nerve, known as V1, V2, and V3. Function can be lost in one or all of these branches.
Cranial Nerve VI: Abducens
We’re half way there! This nerve also controls only one muscle involved in eye movements. This muscle is the lateral rectus.
Cranial Nerve VII: Facial
This is a key nerve involved in controlling the muscles of the face. It controls all of the muscles involved in facial expression. It allow you to smile, frown, wince, and make funny faces at your baby. It also allows taste on the front 2/3 of the tongue, and stimulates several of the salivary glands. This is a key cranial nerve that you do not want to lose control over.
Cranial Nerve VIII: Vestibulochoclear
This is the nerve that allows you to hear. It innervates the inner ear, along with the organs that are involved in hearing and balance.
Cranial Nerve IX: Glossopharyngeal
This is another Jack of all Trades. This nerve handles part of the taste in the tongue. It also handles sensations from part of the pharynx and back of the mouth. It also provides sensory information from the parotid gland a some other important structures in the head and neck.
Cranial Nerve X: Vagus
This nerve provides muscle innervation to most of the pharynx and larynx. It works the vocal chords and the muscles around them. It aids the muscles that are involved in swallowing. The vagus nerve also serves as the major parasympathetic innervation for just about all of the internal organs above the large intestine. The details of what this really means are outside the scope of this article.
Cranial Nerve XI: Accessory
This is cranial nerve controls the muscles in and around the neck. it controls the trapezius. If you loose the function of this nerve, you cannot shrug and you lose much of the ability to move your head about.
Cranial Nerve XII: Hypoglossal
Yeah, the last one! This nerve provides muscle innervation to the tongue. You cannot move your tongue without it. Medical students call it the “kissing nerve”. But only for kissing that doesn’t use only the lips. It also aids in swallowing.
