For several reasons ranging from beautification of the face to the mythical believe that ‘tiroo’ cleanses the eyeballs and guards against any dirt that should have entered the eyes, applying ‘tiroo’ is popular among elderly men and women in the south-western part of Nigeria. The reaction of individual when applying it is similar among the user- the mouth is always open.
That face you make when inserting the rod containing the ‘tiroo’ into the eye is a bizarre human quirk right up there with sneezing in sunlight and contagious yawning. Why do you feel a compulsion to open your mouth when it comes to messing with your eyes? There is no definitive answer, but the leading theory is pretty compelling. Let us get down to it.
Getting this idea requires understanding the anatomy of your head (apologies to anatomists). The muscle mainly responsible for opening and closing your mouth is called the lateral or external pterygoid. It is controlled by the central sensation highway known as the trigeminal nerve. The muscle that lifts and lowers your upper eyelids, on the other hand, is controlled by the oculomotor nerve.
The trigeminal nerve and the oculomotor nerve originate really close together in the brainstem. Apology for all these anatomical jargons. Back to the topic of discussion, the point is those wires (nerves) can get crossed. When you activate the oculomotor nerve to keep your eyes open to avoid making a mess of the ‘tiroo’, you end up activating the trigeminal nerve and opening your jaw and the mouth is opened inadvertently.
Is it now impossible to close the mouth when applying it? No, it is not but that would necessitate deliberate going against the reflex action going on in the brainstem and the mechanism is disturbed.