The eardrum (tympanic membrane) is a delicate sheet of tissue in the middle ear that vibrates when sound waves hit it. The body possesses a mechanism to actively change the eardrum’s tension, often described as “flexing.” This movement is driven by a tiny muscle attached to the auditory apparatus. In some individuals, the ability to control this muscle combines involuntary reflexes with conscious action.
The Muscle That Controls Eardrum Tension
The specific anatomical structure controlling eardrum tension is the Tensor Tympani muscle, one of the two smallest muscles in the body, located within the middle ear cavity. This muscle originates from a bony canal and the cartilaginous part of the auditory tube. Its tendon inserts directly onto the manubrium (handle) of the malleus bone, the first of the three small bones in the middle ear. When the Tensor Tympani contracts, it pulls the malleus bone medially, drawing the center of the eardrum inward. This increases the tension of the tympanic membrane. The effect modifies how sound is transmitted to the inner ear, specifically reducing the transmission of lower-frequency sound waves. The companion muscle is the Stapedius, which acts on the stapes bone to stabilize the ossicular chain.
How People Voluntarily “Flex” Their Eardrums
For most people, the Tensor Tympani is controlled by an involuntary reflex arc, contracting without conscious thought. However, a small percentage of the population can gain voluntary control, allowing them to contract the muscle on demand. Estimates suggest roughly one in ten people can learn this deliberate action.
Individuals with this control describe the resulting sensation as a low-frequency rumbling or roaring sound heard internally, often associated with distant thunder. This internal noise is the audible vibration of the muscle fibers as they tense, or the sound of the resulting pressure change. The contraction changes the eardrum’s resonant frequency, which is perceived as a deep, muffled roar.
Many who voluntarily tense the muscle use a learned trigger, exploiting the muscle’s connection to the trigeminal nerve. Actions like clenching the jaw, squeezing the eyes shut, or yawning can inadvertently activate the reflex pathway. Over time, some individuals isolate the muscular action from the external trigger, producing the rumbling sound at will.
The Biological Purpose of This Reflex
The primary role of the Tensor Tympani and the Stapedius muscles is to work together in the involuntary middle ear reflex. This reflex is designed to protect the delicate structures of the inner ear, specifically the hair cells in the cochlea, from damage caused by loud noises. The contraction of these muscles dampens the transmission of vibrational energy before it reaches the inner ear fluids.
The reflex is typically triggered by sustained, intense sounds above a certain loudness threshold. This process offers protection against noises that last for a period of time, such as loud music or machinery.
The middle ear muscles also contract in anticipation of sounds generated by the body itself, such as before a person speaks or during chewing (mastication). This pre-emptive dampening prevents loud, internally generated sounds from overwhelming the auditory system. Although the reflex helps against ongoing loud noise, its reaction time of around 40 milliseconds is too slow to protect the ear from sudden, sharp noises like an explosion or a gunshot.