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When you yawn, two tiny middle-ear muscles — the tensor tympani and the stapedius — contract reflexively. They stiffen the eardrum and the chain of ossicle bones, so less sound vibration is passed through to the inner ear. The result is the brief moment of muffled, underwater-style hearing you experience mid-yawn. (The Eustachian tube actually opens during a yawn too, but that equalises ear pressure rather than causing the deafness.)
Yawning is one activity that everyone engages in. Although at times it can be rather embarrassing (during a lecture or an important corporate meeting), the act of yawning is one of the most adored activities we humans have. It induces a pleasant feeling of calmness, and let’s admit it, sleepiness.
However, yawning is quite strange. Not only is it contagious, but it also makes you partially deaf for a moment. Why does that happen?
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Reception Of Sound By The Ear
It’s a well-known fact that everything appears dulled for the duration of a yawn; the sounds you hear dramatically drop to nearly silent. The reason for this rather weird phenomenon lies in the activities taking place in the ear during a yawn.
Anatomy Of The Ear
Let’s first see how sound is received and subsequently transmitted to the brain for processing. The ear has three main parts: the outer ear (which includes the ear canal and the eardrum, or tympanic membrane), the middle ear, and the inner ear. When sound waves reach the ear, the changes in air pressure cause the eardrum to vibrate. Those vibrations are passed along by three tiny bones (the ossicles) sitting in the middle ear — the malleus (hammer), incus (anvil), and stapes (stirrup). These small bones work in perfect harmony to transmit the sound to the cochlea in the inner ear, from where it is sent to the brain for interpretation.
Eustachian Tube
Ever heard of the Eustachian tube? It connects the middle ear to the back of the nasal cavity. Several physical acts, like yawning, chewing and swallowing, open the Eustachian tube and allow air to enter or escape the middle ear. In essence, the Eustachian tube helps maintain normalized air pressure in the ear.
How Yawning Affects Hearing
You might guess that yawning works by creating a pressure difference across the eardrum, but it’s actually the opposite. Opening the Eustachian tube during a yawn lets air move in or out of the middle ear and equalises the pressure (which is exactly why pilots and scuba divers use yawns and swallows to clear their ears). The real reason your hearing dips during a yawn is mechanical — a pair of tiny muscles in the middle ear briefly tighten and dampen the whole system. Here’s how that works.
Tensor Tympani Muscle
When you yawn, both the tensor tympani muscle and the stapedius muscle contract. Together, these two are sometimes called the “intra-aural muscles,” and they normally function as a built-in volume control — stiffening the ossicle chain to dampen loud sounds and protect the inner ear.
The function of these two muscles is quite similar to that of the iris; have you noticed how you tend to close your eyes when you suddenly come out form a dark room to a well-lit room? It’s the iris that regulates the amount of light entering the retina. In the same fashion, the tightening of the tensor tympani and stapedius muscles makes the ossicular chain become less able to pass all vibrations of the eardrum to the inner ear. This is why that brief ‘partial deafness’ occurs when you yawn.
Now you know a scientific reason why yawning can be really problematic; especially if you’re listening to an important piece of information that won’t be repeated. Even though it feels great, sometimes it’s better to fight the yawn!
