The balance portion of the inner ear is made up of three semicircular, fluid filled canals which join a larger, globular structure called the vestibule. Similar to the cochlea, the semicircular canals are tubular structures filled with endolymph and surrounded by perilymph. The hardest bone in the body, the labyrinthine bone, surrounds the entire structure. Each semicircular canal is oriented at right angles to the others, comprising superior, horizontal, and posterior (behind) canals. The right and left semicircular canals are mirror images of each other, so that every direction of angular head motion is represented by both ears, oppositely. At the junction of each semicircular canal and the vestibule is a special receptor for rotational movements of the head, referred to as the crista. The crista contains hair cells embedded in a gelatinous matrix, with accompanying nerve fibers.


As the head turns in a particular direction, the fluid within the semicircular canal turns in the opposite direction, thus bending the hair cells and inducing a change in nerve activity. That signal is sent through the vestibular (balance) nerve to the brain where it is interpreted, and adjustments are made in eye movements and postural control. This ensures that the eyes remain on a given target, and that the arms and legs remain in a good position for maintaining stable posture. Within the vestibule are hair cells that respond to changes in head and body movements in the horizontal and vertical planes. These “otolithic” hair cells are covered with a layer of calcium carbonate, making them top heavy and therefore motion sensitive for both linear accelerations and gravitational forces.
Nerve fibers from the crista and the otolithic organs form two large balance nerves, the superior and inferior vestibular nerves. They travel from the inner ear to the brainstem parallel to the cochlear and facial nerves. Within the brainstem they form an extensive neural network involving nerves to the eyes, ears, the cerebellum, and positional receptors “proprioceptors” located in the arms, legs, and neck. The brain interprets this information, and makes modifications in eye, head, and body position to maintain visual (eye) fixation on a target and erect posture. Unfortunately, there are also connections to the thalamic region of the brain, which is responsible for the nausea and vomiting which accompanies most disturbances within the vestibular system. A sensation of vertigo or disequilibrium may accompany any imbalance or dysfunction within this neural network. Symptoms of imbalance or “dizziness” may be experienced by injury to the eye, ear, brain, and proprioceptors from the extremities. Therefore, it is often difficult to determine the exact site of injury based on symptoms alone, and further diagnostic testing is useful.

Balance and Coordination

Balance is the ability to maintain an upright position. Coordination is the capacity to move through a complex set of movements while maintaining balance. Balance and coordination depend on the interaction of multiple systems working together. The primary systems involved with balance and coordination include the vestibular (inner ear), visual (movements of the eyes), and proprioception (commonly referred to as your touch and feel sense). The central nervous system, primarily the brain stem and cerebellum, provides the central processing for the three sensory input systems into one coordinated event, allowing for one output of responses, balanced and coordinated.

As seen above, the three primary balance systems: vestibular, visual, and proprioception individually send signals to each other as well as the brain about head and body movements relative to gravity and rotational movements.

In most individuals, the brain selects the most accurate signals from a combination of the three balance systems; which in theory should be the same information and signals. As the brain interrupts these three input senses, it generates one specific message that is sent back to the muscles of the limbs, torso, neck and eyes to keep us stable and upright. The more signals the brain receives and sends (in milliseconds), the better our balance. If one of the systems is damaged or affected in any way, the other systems must compensate to keep us balanced. Temporary loss of one of these systems can create instability. For example, changes in signals from a damaged inner ear vestibular system (e.g. a concussion) can result in a sensation of dizziness. Similarly, a visual problem that causes blurring or double vision may cause a sensation of unsteadiness or disequilibrium. Also, variations in proprioception seen after an injury, such as sprained or torn ligaments, change your body’s awareness in three dimensional space.
As stated, the signals that the brain receives or sends can be disturbed by changes or fluctuations in these systems, making it difficult to balance or stay coordinated during even daily activities. This is why is may be necessary to get a complete evaluation with specific testing for your vestibular, visual, and proprioception systems to determine the exact cause of your common symptoms and to determine an objective treatment course.


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