The sense of balance is used to orient in three-dimensional space, to determine the position of the body in space, including the limbs, and to coordinate complex movements. The sense of balance is primarily fed by direct feedback from the paired vestibular organs in the inner ear; in addition, feedback from thousands of proprioceptors in muscles, tendons, and ligaments influence the sense of balance. Visual feedback also has a strong influence and can even “override” vestibular stimuli in the short term.
What is the sense of balance?
The sense of balance primarily feeds on direct feedback from the paired vestibular organs in the inner ear. Strictly speaking, the sense of balance involves a complex, composite sensory perception based not only on feedback from a single sensory or sensory organ, but on sensory messages interconnected by the brain from the vestibular organs, the proprioceptors abundant in all muscles, ligaments, and tendons, and the eyes. Auditory sensations and the sense of touch of the skin can also play a role and contribute. First and foremost, however, are the paired vestibular or balance organs in the inner ear. They are composed of three perpendicular arcades and two otolith organs each. The vestibular organs are sensitive to rotational and linear accelerations, which they convert into nerve impulses and transmit via the vestibular nerve to the brain, which processes the messages along with other inputs. Each arcuate duct is specialized for one of the three possible rotational accelerations about the vertical, transverse, or longitudinal axis, while only the two otolith organs sacculus and utriculus are available for the possible three linear acceleration directions forward/backward, sideways left/right, and upward/downward. The gravitational force corresponds to a linear acceleration that is always directed toward the center of the earth and plays an important role in body orientation.
Function and task
Evolutionarily, the sense of balance has the task of enabling and facilitating complex movement sequences for humans, such as walking upright, jumping, running and shimmying in branches, as well as balancing, even in the dark if necessary, i.e., completely without sight. The complex movement sequences are for the most part not innate, but are acquired through practice. A toddler, for example, needs quite a long time to master upright walking safely. Acquiring through learning has the advantage that other complex movement patterns such as riding a two-wheeler or even a unicycle, driving a car and piloting an airplane can also be learned. The learned movement patterns are stored in the multisensory movement memory and can then be recalled at will and even performed unconsciously – almost automatically. After a certain amount of practice, people no longer have to concentrate on cycling, but can talk and relax along the way. While walking upright in complete darkness or with eyes closed is possible, there is no longer good control over the direction in which we walk. Usually a few seconds are enough for a deviation from the straight line to be maintained. The deviation usually results in us slowly turning in circles. Vestibular feedbacks have the great advantage that they are very fast, much faster than visual impressions via the central visual field, and are therefore very well suited as inputs for coordinating and controlling complex movement sequences. However, they have the major disadvantage that they briefly emit false impulses after being acted upon by a stronger acceleration or deceleration, because the endolymph in the arcades or in the otolith organs is still in motion due to inertia. This is the effect experienced by figure skaters or dancers after abruptly stopping a pirouette. The momentary disorientation with lingering sensation of turning can be remedied by fixation of the environment within fractions of a second because the brain uses the visual impression to suppress the “false” angular momentum of the vestibular sense. Conversely, the brain can also provide missing vestibular stimuli, for example, when the eye shows a situation in which acceleration should occur but none is present.Therefore, experienced pilots may well feel acceleration (vection illusion) in a flight simulator with a good visual system without motion during acceleration to takeoff.
Illness and discomfort
The most common problem with the sense of balance is kinetosis, also known as travel, sea or simulator sickness, which is only a temporary phenomenon and manifests itself in a mild form as malaise or in more severe forms by violent nausea and vomiting. Most likely, kinetosis is due to sensor conflicts between the individual sensors, i.e. between vision, vestibular impressions and proprioceptive messages. This includes, for example, that the eyes signal certain situations that are normally coupled with vestibular stimuli, but these are completely absent as in a motionless driving or flight simulator. This may well happen to an experienced visual pilot without simulator experience when flying in a motionless simulator. Vestibular disorders are usually paired with spinning dizziness and nausea, which can progress to vomiting. The most common form of vestibular spinning vertigo is benign paroxysmal positional vertigo, which can be triggered by Meniere’s disease, for example. It is an increased accumulation of fluid in the membranous labyrinth, the seat of the vestibular organs. Permanent vertigo with nausea can be caused by neuritis vestibularis, an inflammation of the vestibular nerve. Symptoms are often accompanied by nystagmus, an involuntary eye movement in a kind of jagged pattern that usually occurs with sustained spinning (e.g., pirouette). Overall, the reasons for the occurrence of vertigo attacks and other balance disorders are very diverse. In many cases, cardiovascular diseases such as high blood pressure (hypertension) and low blood pressure (hypotension) already trigger disturbances in the sense of balance.
