What are the Cranial Nerves?
The cranial nerves are 12 pairs of nerves which begin in the base of the brain and carry information from the brain, through small holes in the skull, to organs and other areas such as the face, neck and chest. As such they control many major functions that are vital to human survival such as swallowing, sight, smell and balance. The cranial nerves are numbered in order of their position from the front to the back of the brain and so they are always listed in the same order:
1. Olfactory. The Olfactory nerves relay sense information from the nostrils and are vital for our sense of smell.
2. Optic. The Optic nerves carry visual information to and from the eyes.
3. Oculomotor. The Oculomotor nerves are also connected to the eyes. They are responsible for pupil constriction and keeping our eyes open.
4. Trochlear. Also vital for proper eye function, the Trochlear nerves are responsible for downward eye movement.
5. Trigeminal. The Trigeminal nerves connect to the lower face and neck. They are vital for sensation in these areas and also important for jaw movement.
6. Abducens. The Abducens are responsible for side to side eye movement.
7. Facial. As you can probably predict, the Facial nerves control muscles in the face, affecting facial movement and expression. They also relay information about taste on the front 2/3 of the tongue.
8. Vestibulocochlear. The Vestibulocochlear nerves transmit information about hearing and balance to and from the inner ear.
9. Glossopharyngeal. The Glossopharyngeal nerves are responsible for swallowing and also for the sense of taste on the parts of the tongue that the Facial nerve does not reach.
10. Vagus. The only nerve pair to extend beyond the neck, the Vagus nerves have many branches which stretch down into the chest. As such they are responsible for regulating many of our automatic bodily functions including: swallowing, speaking, sweating and regulating the heart and lungs.
11. Spinal. Also sometimes called the Accessory nerves, these nerves control muscles in the shoulders and neck which are responsible for flexion and rotation of the head.
12. Hypoglossal. Finally, the Hypoglossal nerves control tongue movements in order to make speech and swallowing possible.
They are described as pairs of nerves because there are two of each nerve type. The brain has two halves (hemispheres) and each hemisphere is responsible for controlling the opposite half of the body. As such there are two olfactory nerves, one for the sense of smell from the left nostril and one for the right; two optic nerves, one for visual information from the left eye and one for the right, and so on.
Each pair of cranial nerves can be classified according to their role as sensory nerves (relaying information about the five senses), motor nerves (controlling movements) or both. Some of these groupings are quite obvious. For instance, Olfactory, Optic and Vestibulocochlear nerves relay information about our senses of smell, sight and hearing, respectively.
It is therefore easy to guess that these are sensory nerves. With their roles in muscle control the Oculomotor, Trochlear, Abducens, Spinal and Hypoglossal nerves are all classed as motor nerves. The remaining nerves (Trigeminal, Facial, Glossopharyngeal and Vagus) can be classed as both sensory and motor because of the many tasks they perform in both areas.
Like the spinal nerves, the cranial nerves are not well protected and can be easily damaged, with catastrophic results. Physical injuries such as a knock to the head, tumours and drug use can all cause damage. As we have seen, the functions they perform are varied but all incredibly important. For instance, damage to an Optic nerve (nerve pair number 2) could result in a complete loss of vision for the eye it connects to. And that is just one of the 12; some conditions could damage multiple nerves at once.
Cranial Nerve Mnemonics
Due to the disastrous nature of cranial nerve disorders and injuries, memorising the cranial nerves is fundamental for those in the medical profession, and could be critical for patients. However, the complicated names, which have Greek and Latin origins, make memorisation difficult, as well as the fact that they should be remembered in their specific order, to make patient assessments run as smoothly as possible.
This is where mnemonics come in. A mnemonic is a system designed to help remember something, such as a song, rhyme or acronym. An example of an acronym to help remember medical information is FAST. This stands for Face Arms Speech Time and signals the signs of stroke.
There is also a lot of evidence supporting the use of songs and nursery rhymes to help memorisation of complex information. For instance Vanvoorhis (2002) found that singing jingles about statistical concepts leads to better performance in statistics exams, compared to reading definitions of statistical concepts aloud.
However, mnemonics are not just used for medical or technical information. Most children are taught to use mnemonic devices from an early age. For instance to help remember the order of the planets: Mercury, Venus, Earth Mars, Jupiter, Saturn, Uranus and Neptune, children may be taught a sentence like My Very Educated Mother Just Served Us Noodles.
This is an example of a sentence mnemonic. The idea is that the sentence is much easier to remember than a seemingly random list of planet names. Once you have (easily, in theory) memorised the sentence, you can use the first letter of each word to remind yourself of the order of the planets.
So we can learn that the 5th planet from the sun must be Jupiter because the 5th word in the sentence (Just) begins with a J.
Evidence from Saber and Johnson (2008) suggests that using a mnemonic device like this is much more effective than simply trying to remember information by repeating it to yourself. In their experiment, students remembered information not just in the short term, but also for months after they learned it.
This shows that mnemonic devices are not just useful for helping us to consolidate the information into our brains, but once consolidated the memory trace is stronger, leading to longer retention.
Following this idea, generations of doctors have passed mnemonic devices down to their students to help them study all sorts of medical information, including the cranial nerves. In this particular case a simple acronym does not really work. The first letter of each nerve name spells “OOOTTAFAGVSH” which is not exactly catchy. It may be tempting to adjust it slightly in order to make it a catchier acronym. However, this would not be advisable.
In order for a mnemonic to be effective, it must have a very clear relationship to the information being learned. Otherwise it could be very easy to create easy to remember mnemonics, but it would be difficult to remember what they mean! For this reason mnemonic sentences are frequently used for the cranial nerves instead. One very old (decades, at least) example goes as follows:
On Old Olympus Towering Top, A Finn And German Viewed Some Hops
Some Say More Money But My Brother Says Big Books Matter Most
The first sentence can be used to remember the names and order of the nerves while the second sentence can be used to remember whether each nerve is a sensory nerve, motor nerve or both. So using the first sentence we can see that the 6th nerve begins with A, which can help us to recall that it is the Abducens. We can also tell from the second sentence that this is a motor nerve.
Mocco and colleagues (2017) state that in order for a mnemonic to be useful, it should itself be easy to remember. If it is not then the learner may be struggling to remember the mnemonic almost as much as they would struggle to remember the list of information. With that in mind, a sentence about an Olympus Tower and Some Hops may have been easy to remember all those decades ago, but it doesn’t seem so relevant in this day and age.
If students have to put so much effort into remembering a sentence that helps them to remember a list, they may as well have just tried remembering the list! For this reason other medical students over the years have created more updated and (hopefully) easier to remember mnemonic sentences. For instance, for the nerve order:
- Oh, Oh, Oh, Tipsy Tracey And Frisky Vicky Got Very Seriously Hammered
- On Occasion Of Tea Three Adult Friends Vomited Gin Vodka Sambuca, Hysterical!
- Old Oprah Occasionally Trots Triumphantly About, Farting Velveeta Globs, Valiantly Spreading Hysteria
For the classification of sensory, motor or both:
- Some Say Marry Money But My Brother Says Big Boobs Matter Most
- Silly Superman Made Mortal Brothers Make Bets Since Both Boys Made Money
Putting the casual sexism of some of them to one side (and there are definitely some much more sexist ones out there), these sentences are without a doubt much easier for most people to remember. Something they all have in common is an attempt to be funny. There is plenty of evidence that information, pictures, videos and so forth which make people laugh will be more memorable (for instance Carlson, 2011 and Schmidt and Williams, 2001).
It is not entirely clear why but it could be because humour makes us pay more attention. Therefore humour can be an important component in any mnemonic device. Thinking specifically about mnemonics for medical practitioners, Skomorowsky has an interesting point.
This is that humour is integral to those in the medical profession, to guard them against the seriousness of the medical conditions they are learning about and coming face to face with on a daily basis.
As previously stated, a good mnemonic sentence is one that is itself easy to remember, preferably with some humour. If a student does not actually find the above examples very funny then they may struggle to memorise them. In which case, using a subject they already know well can be helpful. If it is something they are enthusiastic about then even better.
Fans of Harry Potter will enjoy this version:
On, On, On, They Travelled And Found Voldermort Guarding Very Secret Horcruxes
Severus Snape Meets Malfoy, But Mad Bellatrix Stays Behind Bushes Misusing Magic
These examples demonstrate that mnemonic devices do not need to be at all relevant to the information you are trying to remember. The most important things are in order for them to be effective are 1) that the mnemonic itself is easy to remember and 2) it is easy to link it to the information that needs to be remembered.
So now you know what the cranial nerves are for, as well as a few mnemonic sentences to help remember their correct order and their role. However, if none of those examples are helpful to you, you could always think of a topic that interests you or makes you laugh and try making one up yourself.
You can also apply these techniques to anything you need to memorise. It could be a funny sentence, a rhyme or you could even try making some sort of visual mnemonic. So long as it works for you, it does not matter what it is.