Protective Reflexes

Acoustic Middle Ear Reflex (AMER)

When a loud sound enters the ear, the tensor tympani muscle tightens the eardrum and by using the tendon located between the malleus and incus it shifts the stapes backwards away from the oval window. This action reduces the force transmitted to the inner ear protecting the Organ of Corti and the auditory nerve from damage. However, this process gets less effective with age³.

Figure 1.13: Acoustic Middle Ear Reflex¹²

Figure 1.14: An example of the temporary threshold shift after broadband noise exposure (115dBA, 20 min) ¹³

A  threshold shift is defined as a reduction in a person’s ability to hear meaning that they need a louder sound intensity to be able to hear. Temporary Threshold Shift normally occurs after exposure to a loud sound, as the name suggests it is a temporary condition that may take up to 16 hours to recover. It can be described as “fatigue of the hair cells in the Organ of Corti” leading to the bending over of the hair cells with subsequent inflammation in the base of the hair cells preventing the loud sound from reaching and damaging the auditory nerve. This condition may be accompanied by Tinnitus⁴.