The trigeminal nerve: warning system and air flow monitor

The trigeminal nerve is one of the cranial nerves. It is responsible for providing sensory feedback to the face and the inside of the nose. Sensations like burning (chili), cooling (menthol, mint), warmth (ginger), and also tickling sensations that lead to sneezing. 

Together with smell, or olfaction and gustation (true taste–salty, sweet, sour, bitter, and umami), the trigeminal nerve provides us with information about the food we eat. A meal of foods that are spicy and highly seasoned with peppers, chilis, ginger, or mint, provides an impactful experience of flavour, even when the sense of smell is reduced. Understanding how the trigeminal nerve influences our meals is helpful for anyone with impaired smell who wishes to improve their mealtimes. 

The trigeminal nerve is not only helpful with interpreting what’s on your plate, but also alerts you to things that might be harmful, like strong chemicals. If you catch a whiff of ammonia or bleach (please don’t sniff either of these! They are dangerous to your olfactory nerves!) you’ll get a powerful unpleasant sensation. This can also happen if you’ve drunk a fizzy drink too quickly and burp up the CO2 through your nose. 

Dr Basile Landis, head of the Rhinology department at Geneva University in Switzerland, said this to me in a previous interview: 

The sensory system that detects threats is the trigeminal system which is governed by the trigeminal nerve. It’s the system of touch for the inside of the nose. For instance, if the air is causing burning, stinging, prickling, like after sniffing pepper, that is potentially harmful and you should not inhale. The nose detects that.

Another function of the trigeminal nose is to provide perception of air flow. Take a breath now through your nose. You’ll feel the air going in through your nostrils. If you had some dental work to your upper teeth near your nose, the numbing injection might affect the way you feel the air passage in your nose. If that happened, you might feel that your nose is congested and blocked, because the trigeminal nerve is temporarily numbed–you wouldn’t be able to feel the air going in and out. 

Landis commented:

Normally, inhaled air creates resistance with the mucosa and this creates a touch

feeling. When you inhale, although you don’t think about this consciously, the brain

creates a feedback loop which tells how much air you are experiencing--free airflow

makes us feel comfortable. Using a menthol inhaler artificially stimulates the

trigeminal nerve and gives you the impression that more air is passing over the airways in your nose and this gives you the feeling of comfort. But this is only an

impression. Menthol inhalers do not “free up” your upper airways.

The trigeminal nerve also serves the eyes. According to Landis: 

The eyes also use the trigeminal nerve. When you cut onions, you may have teary eyes and start sneezing or have a runny nose, for instance. That’s because onions contain an aggressive

volatile compound. And this system also generates reflexes. For instance if you

breathe in pepper, you will cough or sneeze.

So the next time you sneeze, cut onions, or eat a hot chili, think about your trigeminal nerve! It supports many perceptions that go hand in hand with smell. 

image courtesy of my.clevelandclinic.org (c) 2023