The ear can be divided into three areas, and these are the external ear (also known as the pinna), the middle ear and the internal ear. These areas of the ear function as follows:
- The external portion of the ear is partially responsible for allowing a child to determine the location for sound, whether it is behind, above, below or ahead of their position.
- The pinna is also responsible for funneling and concentrating sound waves as they pass into the middle ear.
- The middle ear contains the auditory canal, which ends near the eardrum, which is also referred to as the tympanic membrane.
Structure of the ear
On the opposite side of the eardrum are three small bones which are referred to as ossicles. The three bones which comprise the ossicles are called the malleus, incus and the stapes. The ossicles are attached to the cochlea, which is a structure filled with fluid in the internal ear.
The cochlea is one of the most important parts of the ear, as this is where the transmitted vibrations sent through the eardrum are transformed into electrical signals which are sent through the auditory nerve into the brain. The internal ear, which is encapsulated by bone, contains a number of canals which are designed to provide equilibrium for hearing.
The ossicles within a child’s ear can become stiff and muted through a contraction within the stapedius muscle. This gives them a degree of protection against loud noises which are sustained, but provides less protection against sudden, sharp noises. This reflex within the ears of children is much more efficient than in older people, which is one of the reasons why the elderly have less tolerance for loud music, as well as a greater chance for developing hearing loss.
The basilar membrane and organ of Corti
The hearing perception of the ear is concentrated in an area referred to as the basilar membrane. This membrane is found within the cochlea, which is itself a tube with a tapered shape. The basilar membrane splits the tube along its length into double canals which are filled with fluid. The two canals are tapered near their ends, and the ossicles send vibrations for the cochlea which are then connected to the oval window. The waves are then transmitted to the basilar membrane where they are detected by as much as twenty thousand hair cells called cilia which reach up from a canal called the organ of Corti.
The organ of Corti is responsible for transforming the hair cells which are stimulated into the nerve impulses. Because the cochlea utilizes a tapered design, this means that the waveforms which are sent to the basilar membrane increase in amplitude at various points based on their frequency. Increased frequencies will peak at shorter distances than frequencies which are lower.
Because the cochlea has a shape which is tapered, the distance between the pitches will use the same distance as the perception of pitch. The reason for this is because higher frequencies are capable of masking or even hiding lower frequencies.