The inner ear has a structure called the labyrinth, which is a combination of bone and soft tissue that controls balance. It is a maze-like structure, made up of three fluid-filled looped ducts that send signals to the brain when the head moves.
Inside each loop is a flexible structure called a cupula, which stretches across the duct like a drum head. In back of the cupula are sensory hair cells that have tiny extensions, called stereocilia, brushing against the cupula. When the head turns, the fluid inside each duct moves. The cupula bends and the stereocilia flex, sending messages to the brain about the direction of movement.
Between the loops and the cochlea are two fluid-filled pouches, the utricle and the saccule. Both organs also have sensory hairs and otoconia, which are grains of calcium carbonate. The fluid, hairs and grains tell the brain how the head movements relate to gravity. They can tell if the head is moving forward or sideways and if the person is sitting up, lying down or just leaning back.
The inner ear's labyrinth is the beginning of the vestibular system, which includes the eyes and the sensory portions of the musculoskeletal system. If any of these systems is malfunctioning, it creates balance issues which can lead to falls and injuries.