The ear is sensory organ that detects sounds. The range of hearing is differentiates from species to another. Dogs are able to use their keen sense of hearing to hear minute disturbances within its atmosphere. A bat, whose auditory ability exceeds greatly in comparison to a dog, uses their ears to fly in the dark and avoid obstacles that it unable to perceive via vision. In general, the human ear is structured accordingly so that we can be aware of our surroundings acoustically. The ear is classified into three basic structures. That is, the outer ear, middle ear, and inner ear assemble the essential sub-organ components to hearing. The outer ear is the exterior component of the ear which coax sounds waves into the ear. It is composed of the auricle, the ear canal, and the tympanic membrane known today as the eardrum. In animals, the auricle possesses skeletal muscles that move to ear a distinct sounds. For humans, to focus on a particular sound requires a mental honing of neurological circuits of the central nervous systems. Then, the sounds travel through the ear canal and meet the tympanic membrane. (www.wikipedia.com)
After tympanic membrane, the middle ear structures appear. ...
In humans and other land animals, the middle ear is normally filled with air. Unlike the open ear canal, however, the air of the middle ear is not in direct contact with the atmosphere outside the body. The Eustachian tube connects from the chamber of the middle ear to the back of the pharynx. (saladin, pg. 598) The middle ear is very much like a specialized paranasal sinus, called the tympanic cavity; it, like the paranasal sinuses, is a hollow mucosa-lined cavity in the skull that is ventilated through the nose. The mastoid portion of the human temporal bone, which can be felt as a bump in the skull behind the ausicle, also contains air, which is ventilated through the middle ear.
The inner ear is formed by the vestibule, semi-circular canals, and cochlear. The fluid in the cochlear absorbs vibrations from the stirrup and transfers it to the vestibule. Vestibular hair cells are stimulated by movement of fluid in the semicircular canals and the utricle and saccule. Firing of vestibular hair cells stimulates the Vestibular portion of the eighth cranial nerve. Hair cells are also the receptor cells involved in balance, although the hair cells of the auditory and vestibular systems of the ear are not identical. (saladin, pg. 600) The eighth cranial nerve comes from the brain stem to enter the inner ear. When sound strikes the ear drum, the movement is transferred to the footplate of the stapes, which presses into one of the fluid-filled ducts of the cochlea. The fluid inside this duct is moved, flowing against the receptor cells of the organ of Corti. These stimulate the spiral ganglion, which sends information through the auditory portion of the eighth cranial nerve to the brain. (Saladin,