ear

the sense organ used for detection of sound and maintenance of balance. It comprises three parts: the external or outer, the middle and the inner ear, the first two acting to collect sound waves and transmit them to the inner ear, where the hearing and balance mechanisms are situated. The outer ear (auricle or pinna) is a cartilage and skin structure that is not actually essential to hearing in humans. The middle ear is an air - filled cavity that is linked to the PHARYNX via the EUSTACHIAN TUBE . Within the middle ear are the ear(or auditory) ossicles, three bones called the incus malleus and stapes (anvil, hammer and stirrup respectively). Two small muscles control the bones and the associated nerve (the chorda tympani). The ossicles bridge the middle ear, connecting the eardrum with the inner ear and, in so doing, convert sound (air waves) into mechanical movements that then impinge on the fluid of the inner ear. The inner ear lies within the temporal bone of the skull and contains the apparatus for hearing and balance. The COCHLEA is responsible for hearing, and balance is maintained by the semicircular canals. These are made up of three loops positioned mutually at right angles, and in each is the fluid endolymph. When the head is moved, the fluid moves accordingly, and sensory cells produce impulses that are transmitted to the brain.