The loud rumbling sound (sometimes like thunder) that’s produced in the ear when you close your eyes too tightly is due to the contraction of a muscle called the tensor tympani muscle. It is a muscle located within the ear and it functions to dampen certain sounds.
Some of you may have observed that when you shut your eyes really tight, there’s a rumbling sound produced in the ear. It’s a low frequency sound that can only be felt by the individual in question. Note that the sound is not heard by anyone else.
What is that sound? Where does it come from?
Tensor Tympani Muscle
The tensor tympani is a muscle inside the ear, located in the bony canal above the osseous portion of the auditory tube. It’s attached to the upper part of the handle of the malleus and pulls the tympanic membrane inwards when it vibrates.
As you can see in the figure above, the tensor tympani muscle arises from the superior surface of the cartilaginous portion of the auditory tube, and the adjacent part of the greater wing of the sphenoid and petrous part of the temporal bone (refer to the diagram below). It passes backwards through the canal and culminates in a slim tendon that enters the tympanic cavity.
There are two muscles in the tympanic cavity, the tensor tympani and the stapedius, wherein the former is the larger one.
Functions of the Tensor Tympani Muscle
The tensor tympani muscle dampens certain sounds, such as those produced when chewing. The two muscles present in the tympanic cavity reflexively dampen ossicle movement to suppress forceful low-frequency sounds.
Just imagine how irritating it would be if you could constantly hear the sounds produced inside your mouth while chewing.
Although you still hear those sounds, they’re greatly dampened by the tensor tympani muscle present inside your ears.
What happens when you shut your eyes too tightly?
When you squint or shut your eyes too tightly, the tensor tympani muscle contracts and tightens the eardrum through a tendon, which shifts the stirrup backwards from the oval window to the inner ear. This results in a reduction of the magnitude of force transmitted to the inner ear and protects it from loud sounds.
It’s interesting to note that when you contract muscles, vibrations and low-frequency sounds are produced. This is just like when you flex your arm, as you can actually see the muscles moving/vibrating.
Similarly, when you shut your eyes too tightly, the same thing happens inside your ear. Slow-twitch fibers produce sounds in the frequency range of 10-30 Hertz, while fast-twitch fibers produce 30-70 Hertz sound frequencies (Source). Note that the generally accepted audible range for humans is 20 to 20,000 Hertz, although this audible range may vary depending upon individuals and various environmental factors.
The sound of muscle contractions can be heard directly by flexing a muscle (e.g., a firmly clenched fist) and pressing it against the ear. Similarly, the sound of a contraction of the tensor tympani muscle can be heard by shutting one’s eyes tightly, or enjoying a deep yawn (as jaw muscles are highly tensed when one yawns deeply).
However, it is important to note that not everyone can produce this rumbling, thunder-like sound in their ears voluntarily by contracting the tensor tympani muscle; only a small percentage of people can actually do that. Therefore, don’t keep shutting your eyes tightly in the hopes of hearing thunder rumbling in your ears!