Since the beginning of life on earth, gravity has been ubiquitous. To counteract against this force pulling one down, species were compelled to develop a system. The plant species solved this problem as they had roots anchoring them to solid ground. With evolution, mobile species were faced with the complex issue of not only sensing gravity and orient themselves to an infinite space at a given point of time but also to sense and resolve a change in centre of gravity that was integral to movement. A simple way to perform this act was to devise a system that would incorporate a counterweight with calcium crystals. Even the lowliest form of life on the seabed will have some of these crystals that are derived from the seabed. As life evolved further in the sea and graduated to land, the function of this system became more elaborate and complex and thus evolved the vestibular system. The earliest closed vestibular system occurred in primitive fish and predated mammalian cochlear development by a million years. This is not unsurprising as orientation in space is a primitive reflex for survival rather than hearing. It can be appreciated that the vestibular system will thus consist of two distinct type of sensors – a group of sensors to sense and resolve gravity and a group of sensors to sense and resolve the change of centre of gravity, i.e. movement.

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The human vestibular organ is located in the deep parts of the skull in the temporal bone in the region known as the labyrinth and just behind the hearing sense organ cochlea. It consists of 5 distinct organs – the 2 gravitational sensors or otolith organs the saccule and the utricle with their calcium crystals called otoliths and the 3 motion sensors the semicircular canals that depending on the orientation of movement are the anterior/superior (front/up) semicircular canal, the lateral (side) semicircular canal and the posterior (behind) semicircular canal.

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Their function is through the movement of the tiny cells resembling hair (hence called hair cells) located in their intrinsic membranes called the sensory epithelia.  It is a tiny organ and mention of the sizes of its components will give an idea. The utricle and the saccule on an average are 2.7mm in length and the former is 2.2 mm and the latter is about 1.2 mm in breadth. The posterior semicircular canal is the longest at 18mm whilst the others are about 15 mm with a diameter of 1-6mm. This tiny organ resolves 60% of human balance whilst the visual system and the proprioceptive system account for 20% each. All the three sensors send their information to the brain who integrates and analyses the information and generates the final balance perception.

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The function of the human vestibular system is not limited to only resolving balance and orientation in space but also critically stabilising gaze, navigation, peripheral muscle tone, cognition and autonomic control. This is achieved by a series of reflexes that originate in the vestibular system and affect the peripheral sites like the eyes, the neck and the spine. In a child, a properly functioning vestibular system is required for normal motor development, postural stability and importantly cognitive and overall development. It is crucial for children to participate in childhood playground activities. Therefore, a deficit in such vestibular function will affect all these domains disrupting quality of lives in children.

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Perceptual balance disorders can arise due to many conditions in the vestibular system, in the brain, in the eyes, in the heart and in the musculoskeletal system or even psychogenic disorders. The adult population differs from the paediatric population in presentation, causes, natural history and treatment of vestibular conditions. This is because a child’s brain and vestibular system are in the developmental stage and behave differently than adults until reaching maturity.

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Objective quantification of vestibular response in different frequencies of movement can be performed now with immense development in vestibular diagnostics. This means that vestibular tests can be eminently performed in children of most age groups. This requires skills and expertise and a solid grounding in paediatrics. Sine the vestibular-neurology and ophthalmology interface is overlapping, knowledge is desirable in these fields too in addition to knowledge in many paediatric medical disciplines like cardiology, rheumatology, endocrinology, oncology and developmental paediatrics.