Sound waves are traveling vibrations of air that consist of alternating regions of high pressure (caused by compression) and low pressure (caused by rarefaction) of the air molecules.
Regions of compressed air and regions of rarefied air
These disturbed air molecules have the ability to disturb adjacent air molecules setting up new regions of compression and rarefaction as they go. This wave/ripple is then carried until the energy is lost and it dissipates (the sound disappears).
Sound waves are sinusoidal waves and they have two main characteristics:
We are able to perceive different types of sounds; sound patterns that are repeated over time are perceived as musical (or make sense) whereas aperiodic sounds that are non repeating code for noise.
The ear is partitioned into 3 distinct anatomical regions, the external ear, the middle ear, and the inner ear.
The external ear is the skin covered part of the ear that we are familiar with, which is made-up of a funnel shaped pinna and a canal known as the external acoustic meatus. The main function of the external ear is to direct sound waves into the ear canal (hence the shape of the pinna). The external acoustic meatus, is hairy and produces a wax-like secretion, known as cerumen. Cerumen combines with dead cells to form wax which helps to inhibit microbial growth and to trap dust.
The middle ear is made up of:
The tympanic membrane is in contact with the auditory ossicles which is subsequently in contact with the oval window. The function of the tympanic membrane and the auditory ossicles is to amplify sound waves that are received from the external ear (they transmit almost 200 fold the pressure that they receive from the external ear into the into the inner ear).
Two mechanical processes occur within the middle ear to achieve this large pressure gain. The first and major boost is achieved by focusing the force impinging on the relatively large-diameter tympanic membrane onto the much smaller-diameter oval window (the site where the bones of the middle ear contact the inner ear). A second and related process relies on the mechanical advantage gained by the lever action of the three small, interconnected ossicles (basically how they are shaped). The inner ear is made-up of two parts, the vestibular part (responsible for equilibrium and balance) and the cochlea part (responsible for hearing).
