Balance is an ability to maintain body in control with minimal body sway (line of gravity within their base of support), in which all acting forces are cancelled by each other resulting in a stable balanced system. The CNS receives feedback about the body orientation from three main sensory systems (somatosensory, vestibular and visual systems) and integrates this sensory feedback and subsequently generates a corrective, stabilizing body by selectively activating muscles.
Main somatosensory systems pathways and proprioceptive information from spino-cerebellar pathways, processed unconsciously in the cerebellum, are required to control postural balance. Proprioceptive information has the shortest time delays, with monosynaptic pathways that can process information as quickly as 40 – 50 ms and hence the major contributor for postural control in normal conditions.
The ability to maintain balance is a result of multidimensional co-operation of brain and CNS.
The vestibular system generates compensatory responses, control and movement to via:
- Postural responses (Vestibulo Spinal Reflex) – keep the body upright and prevent falls when the body is unexpectedly knocked off balance.
- Ocular-motor responses (Vestibulo Ocular Reflex) – allows the eyes to remain steadily focused while the head is in motion.
- Visceral responses (Vestibulo Colic Reflex) – help keep the head and neck centered, steady, and upright on the shoulders.
To achieve this the vestibular system measures head rotation and head acceleration through semicircular canals and otolith organs (utricule and sacule). Visual System to postural control is partially redundant as the visual information has the longer time delays as long as 150 – 200 ms. The influence of moving visual fields on postural stability depends on the characteristics of the visual environment, and of the support surface, including the size of the base of support, its rigidity or compliance.