 Hi, welcome to Physiology Open. Sound is the perception of variations in air pressure produced by anything which vibrates. The variations in air pressure are transmitted via external air to the tympanic membrane. Then to middle air which has three ossicles and then to inner air. So the air pressure vibrations basically vibrate the tympanic membrane which then moves the inverse and outwards at the same frequency as that of the air pressure wave. Now these vibrations of tympanic membrane vibrate the middle ear bones that is malleus, incus and steppes. Malleus is attached to tympanic membrane and steppes is attached to the oval window. So when steppes vibrates it causes vibrations in inner ear fluid. See the external ear and middle ear are filled with air while the inner ear is filled with fluid. Inner ear has cells which need to be present in a homeostatic environment so it needs to be fluid filled. But you might be wondering what is the need of this complicated movement of air pressure wave from external ear to middle to inner ear. Why not directly reach the inner ear from the environment? See when sound pressure wave travel from one medium to another denser medium or a high impedance medium these waves tend to be reflected back. This reduces the energy or amplitude of vibrations reaching the high impedance medium. So if sound pressure waves were to directly hit the receptors present in fluid filled inner ear the sound energy will be too less because most of it would have been reflected. So instead there is a mechanism which actually amplifies the signal before it reaches the inner ear. Such that the expected loss of signal which is going to happen due to the impedance is balanced by its amplification. That's why it is known as impedance matching. The loss happening due to impedance is matched with the amplification. So how does it occur? Fundamentally we have to increase the pressure changes in air. Now if you remember pressure is equal to force upon area. So pressure increase can occur either by increasing the force or decreasing the area. So this occurs by three mechanisms. Area advantage, curved membrane and liver action. All of which are happening in this area of the ear which includes the otim panic membrane and the full middle ear. This one works by decreasing the area where air vibration strikes while the other two work by increasing the force with which they strike. Area advantage occurs because of the difference in area of timpanic membrane and steppes. The area of timpanic membrane is 20 times more than the area of the steppes. Hence the vibrations are being concentrated over a smaller area from a very large area. So this will increase the air pressure level 20 times as it reaches inner ear. Now let's see how the other two factors increase the force. The timpanic membrane is curved to from its rim at both ends to its attachment with the malice. When timpanic membrane vibrates this point of ear drum doesn't move as far as these portions. So with the same sound energy hitting the different areas here it is manifested as increased distance of movement while here in the center it is manifested as increased force. So this is the curved membrane effect and finally when timpanic membrane vibrates it causes vibration of the ear ossicles as we have already discussed. But since malice is longer than incus it displaces incus with a greater force. Remember again that displacement distance is lesser but force of displacement is increased just like curved membrane effect. So impedance matching occurs by three mechanisms and all these three mechanisms together increase the pressure output by 46 times. But this amplification may be harmful if it also occurs for very loud sounds. So that means it should not occur for such sounds. Middle ear contains two muscles tensor timpani and steppidius muscle. Very loud sounds initiate a reflex contraction of these muscles and on contraction tensor timpani pulls malice inwards and steppidius pulls steppice outwards making the ossicles rigid and preventing their vibration. So this decreases the transmission of sound energy thus preventing a rear from damaging sounds. But acute loud sounds do damage ears isn't it? Why? Can you think about this question and put your answers in the comment section? We can have a little chat about it then. Anyways contraction of these muscles is also simultaneously activated when we start speaking. That's why our own voice is perceived less loud. So this is how impedance matching is helpful also and is inhibited for loud sounds and for our own voice. So do let me know your feedback and suggestions on the video and if you liked it do like and share the video and don't forget to subscribe to the channel Physiology Open. Thank you.