Hearing

     The ear provides humans with a remarkable range of hearing.  The ear may be divided up into three regions, the inner ear, the middle ear, and the outer ear.  The only two regions of the ear that are solely responsible for hearing are, the outer ear and the middle ear.  The inner ear regulates equilibrium, balance, as well as hearing. 

     The outer ear is solely composed of the ear canal, the external auditory canal, and the pinna.  The pinna is the structure composed of cartilage, the rests on opposite sides of the head.  The purpose of the pinna is to funnel sound waves into the external auditory chamber.  The external auditory chamber is a small, narrow chamber that is carved into the temporal bone of the skull.  Within this chamber are glands that regulate the secretion of cerium, commonly known as earwax.  When sound enters the external auditory chamber it is reflected to the tympanic membrane, commonly known as the eardrum.  When sound hits the eardrum it causes it to vibrate. 

     The middle ear, also known as the tympanic cavity, is a small air filled cavity within the temporal bone.  The middle ear houses the auditory tube.  The auditory tube runs from the ear, to the throat, where it connects, being lined with mucous.  The auditory tube regulates the pressure of the ear, and has adapted itself to accommodate any changes in the pressure of the ear.  The middle ear houses three of the smallest bones in the body, the hammer, the anvil, and the stirrup.  When the eardrum vibrates it transfers this vibration to the hammer, the anvil, the stirrup, and finally presses against the oval window inside the inner ear.

     The inner ear, also known as the osseous labyrinth.  The inner ear may also be divided into three regions, the cochlea, the vestibule, and the semicircular canals.  These regions are responsible for transforming the vibrations to nerve impulses that can be sent to the brain.  The inner ear also holds the perilymph.  Inside the perilymph is the membranous labyrinth.  These structures contain a number of sacs follow the shape of the bony labyrinth.  These two structures are responsible for equilibrium, or balance.  In the sacs of the perilymph rest receptors known as maculae.  The maculae are responsible for balance.  When the sacs of the ear are turned to a new position, the maculae turn.  When the maculae turn, the gel in the inner ear is pulled, resulting in an impulse to the vestibular nerve, which notifies the brain of the change of position.