Why do we feel a spinning sensation after un-mounting from a merry-go-round?
K. SRINIVASAN
Chennai
All living creatures which have capacity of locomotion, monitor their body orientation and balance with respect to the effect of gravity. Creatures are able to adjust their orientation with respect to self generated movements, as well as forces that are exerted upon them from the outside world. These functions are carried out by the vestibular system. It engages a number of reflex pathways that are responsible for making compensatory movements and adjustments in body position.
The vestibular system in humans resides in the inner ears. The membranous labyrinth of the inner ear consists of three semicircular ducts (horizontal, anterior and posterior), two otolith organs (saccule and utricle), and the cochlea.
The three pairs are oriented roughly 90 degrees to each other for maximum ability to detect angular rotation of the head. When the head turns, fluid in one or more semicircular ducts pushes against the cupula and bends the cilia of the hair cells. Fluid in the corresponding semicircular duct on the opposite side of the head moves in the opposite direction. When we are a riding merry-go-round, our body experiences a centrifugal force due to its circular rotation.
The centrifugal force is sensed by our vestibular system. If the centrifugal force continues for some time, the vestibular system adjusts in such a way that it does not feel the force any more.
However as soon as we dismount from the merry-go-round, the centrifugal force also disappears.
The disappearance of the centrifugal force is sensed as an opposite force applied on the body. This gives us a spinning sensation for some time. Our body again adjusts to the new situation and with that the sensation of the spinning force also disappears after a few minutes.
S.P.S. JAIN
Former Member, Engineering, Indian Railways Greater Noida, Uttar Pradesh
