The temporal bone and the ear
The pinna or auricle is the most external portion of the ear. Itcommunicats via the external auditory canal to the middle ear. The middle ear contains the tympanic membrane, the middle ear bones, a muscle, and ligaments which are not shown in this diagram. The internal cochlea (auditory portion ) as well as the labyrinth (for balance and equilibrium) constitutes the entire inner ear .
Resonant Chamber
The bones of the middle ear form a suspension bridge-like structure between the tympanic membrane and the oval window of the cochlea. The pressure in middle ear cavity is controlled by a tube to the larynx reason why when the body goes into high altitude there is the need to release the pressure. Without the support of the middle ear muscle and ligaments, the bones will move freely and without control. The hammer and the anvil are anchored to the temporal bone by ligaments, and stirrup is attached by a muscle to the temporal bone. Contractions of the muscle and ligament causes rigidity and support to the entire bridge-like structure restricting movement in various directions.
Reduction & Amplification.
The tympanic membrane is 15 to 30 times larger than the oval window where the stirrup is connected to the cochlea itself. Such reduction concentrates force from the initial mechanical displacement of the middle ear in such a way that the tympanic membraneąs initial force is amplified in a similar manner as a womanąs weight is condensed on a heel of a shoe. In other words, if a person weighs 100 lbs. and sat on the floor the mark left would be unnoticed, however if the same weight is place on the heel of one shoe, the mark would be noticeable once the person moves.
Frequency Selectivity
Different sound makes the basilar membrane move with different amplitudes and at different locations. The thickness of the basilar membrane (BM) in the basal segment is 3X thicker than the apical segment. For this reason, sounds of high frequency move the basal segment very lightly. The basilar membrane is 5x wider in the apical segment than in the basal segment. This diagram illustrates that the thickness and width of the basilar membrane allows sound of different frequencies to travel from the base to the apex at different speeds.