How to Identify the Cranial Nerves

What is a Cranial Nerve?

While there are many details about the human body that factor into how humans function from day to day and how the systems in our body allow us to move, breathe, eat, fight off infection, etc., the human brain in itself is a unique masterpiece. It is, in my opinion, the singular organ that makes us who we are. Without our brain, there would be no intellectual functioning. While many pieces come together to create the brain processes, the use of cranial nerves (CNs) have major impacts on how we not only live but thrive throughout our days. 

The cranial nerves are located underneath the brain and connect them with varying parts of the head, neck and trunk. There are twelve of them in total and each serve a specific purpose which will typically fall under the category of sensory, motor, or in some cases, both. The sensory nerves are the Olfactory, Optic and Vestibulocochlear nerves. The motor nerves are the Oculomotor, Trochlear, Abducens, Accessory and Hypoglossal nerves. The nerves that affect both sensory and motor include the Trigeminal, Facial, Glossopharyngeal, and Vagus nerves.

Each of the CNs is numbered in roman numerals from I-XII (1-12). Their number and function are as follows:

• (I) Olfactory Nerve: This provides you with your sense of smell.
• (II) Optic Nerve: This provides you with your sense of vision.
• (III) Oculomotor Nerve: This has two functions:
  A) Motor function to four of the six muscles around the eye
  B) The response of the pupil as it interacts with light
• (IV) Trochlear Nerve: This controls the superior oblique muscle which controls and eye's downward, outward and inward movement.
• (V) Trigeminal Nerve: This is the largest of the cranial nerves and is split into 3 divisions:
  1) Ophthalmic- sensory information is relayed to the upper part of the face (forehead, scalp, upper eyelids)
  2) Maxillary- sensory information is relayed to the middle part of the face (cheeks, upper lip, nasal cavity)
  3) Mandibular- Both sensory and motor; sensory information is relayed to the ears, lower lip and chin; controls the movement of muscles within the jaw and ear
• (VI) Abducens Nerve: This controls the lateral rectus muscle which is another muscle used for outward eye movement.
• (VII) Facial Nerve: This is both sensory and motor and allows for:
  - muscle movement involved in facial expressions and some in jaw
  - providing taste for the tongue
  - supplying glands in the head and neck area (salivary and tear-producing)
  - sending sensations from the outer ear
• (VIII) Vestibulocochlear Nerve: Sensory functions for hearing and balance broken in 2 divisions:
  1) Cochlear- Detect vibrations from sound based on volume and pitch, which is then sent to cochlear nerve
  2) Vestibular- Able to track linear and rotational movements of the head which is sent to vestibular nerve to allow for equilibrium and balance.
• (IX) Glossopharyngeal Nerve: Both sensory motor functions allows for:
  - sending sensory info from sinuses, back of throat, parts of the inner ear and back of tongue
  - sense of taste for the back of the tongue
  - stimulates the voluntary movement of the stylopharyngeus (at the back of the throat)
• (X) Vagus Nerve: Both sensory and motor functions allow for:
  - conveying sensation info from the ear canal to parts of the throat
  - sending sensory info from organs in the chest and trunk (heart, intestines, etc.)
  - motor control of muscles in the throat
  - stimulation for muscles of the organs in the chest and trunk
  - a sense of taste near the root of the  tongue
• (XI) Accessory Nerve: This controls the muscles in your neck.
• (XII) Hypoglossal Nerve: This controls the movement of most muscles in the tongue.

** The colors of each nerve corresponds to its position on the image below**

Source: https://teachmeanatomy.info/head/cranial-nerves/summary/

How To Identify The Cranial Nerves on an Image

Because there are so many cranial nerves and they are all close together, it can seem really overwhelming when trying to memorize and identify which nerve is which on an image. However, the CNs are numbered in the order that they are placed in from the anterior part of the head (the top part of the image above) to the posterior part of the head (bottom part of the image above), with the exception of CN XII. So with that being said, if one can remember the order of the cranial nerves, that could increase your chance of being able to memorize their location.

In order to help me remember the numerical order, I created a mnemonic device:

 

• Only ..........(Olfactory)
• One ...........(Optic)
• Of ..............(Oculomotor)
• The ............(Trochlear)
• Two ...........(Trigeminal)
• Actors ........(Abducens)
• Filmed ........(Facial)
• Very ...........(Vestibulocochlear)
• Good ..........(Glossopharyngeal)
• Very ...........(Vagus)
• Accurate .....(Accessory)
• Hits .............(Hypoglossal)

While many of the letters are the same, this can at least provide a path for me to follow in order to figure out which same-first-lettered nerve belongs in which spot. 

It can also be helpful to think about the purpose that the nerve is serving in order to decipher its location, for some of the nerves. For example, CN I is the Olfactory Nerve which allows for a sense of smell. For this, I think about the nose being the facial feature that extends the furthest and associate that with being the most anterior on the face just like its corresponding nerve is the most anterior under the brain. Similarly, the CN V is the Trigeminal Nerve and I am able to remember this due to the fact that "tri" means three and so the Trigeminal has three branches coming off of it that are visible in images. Another CN nerve correlation is with the Vestibulocochlear Nerve which supports sound, so naturally it is located near where the ear canals are in the skull.

While there is no absolute hack for learning and remembering the locations of all the cranial nerves, these are some of the tips and tricks that have helped me familiarize myself with them. 

If you are looking for an additional resource, below I will include a link to a website that provides a 3D interactive diagram of the cranial nerves that can be looked over:

• Link to Website (Scroll down until you find the diagram towards the bottom of the page):
  
  3D Interactive CN Diagram
  
  

I hope this page has given readers some helpful aids on how to identify the 12 Cranial Nerves.