The Ear: Structure and Function
The ear performs the critical task of converting the mechanical energy of sound and motion into electrical signals that travel to the brain.
The ear is divided into three regions: external, middle and inner.
The external ear includes the part we can see – the auricle – which acts as a collection point for sound waves, concentrating them through the ear canal, not unlike a small megaphone. At the end of the ear canal lies the eardrum, a thin membrane about the size of your pinky fingernail that vibrates when struck by sound waves.
The middle ear is an air space behind the eardrum, where sound waves are converted to mechanical energy through a linkage of the three smallest bones in the body, the ossicles – the hammer (malleus), anvil (incus) and stirrup (stapes). When sound waves strike the eardrum, the vibrations move through this linkage of bones where they are amplified and transferred to the fluid-filled inner ear.
The inner ear has two division, one for hearing (the cochlea) and one for balance (the vestibular labyrinth). In the cochlea, the sound-generated pressure waves traveling through the cochlear fluids stimulates hair cells that convert the mechanical movements to signals traveling in the auditory nerve to the brain. In each ear the vestibular labyrinth has three semicircular canals thta detect rotational motion and two otolith organs that detect linear motion. Head movements cause fluid shifts in the vestibular labyrinth that stimulate vestibular hair cells. The hair cells convert these movements to nerve signals in the two vestibular nerves. The cochlear and vestibular nerves, along with the facial nerve that moves the facial muscles, exit the inner ear via the inernal auditory canal and pass into the brainstem.
The anatomy of the ear is closely related to a number of other structures, including the joints of the jaw, salivary glands, the facial nerve – controlling the muscles of the face, the carotid artery, jugular vein and associated cranial nerves which pass from the inside of the skull to the neck.