Ringa Ringa Roses

Most of us remember this:
Ringa ringa roses,
Pocket full of posies
Husha busha!
We all fall down!

There are two kinds of people;

• The first kind hold hands and go round and round singing this
• The second (and the cooler) kind, just spin around in their places till… they all fall down!

Spinning is a regular part of certain activities, like dancing and also playing (for both children and adults). But why does it cause dizziness? Today’s question:

Why Does Spinning Make You Dizzy?

The answer, in short (for the intelligent and yet foolish physicists with no idea of the beauty of biology) is “The principle of Inertia”: nature resists change. An object at rest, will stay at rest until something forces it to budge, and if it’s moving, it will keep moving until ground to halt.

Now, for the more informed of people, here is a biological explanation. In the labyrinthine structure of the inner ear, there are three “semicircular canals” arranged at right angles to one another, so that each sense the movement of your head along a different axis. All three collaborate to orient you in 3D space. The canals are filled with a fluid that sloshes around as you move. Your ears sense motion by detecting the way tiny strands of hair lining the canals wave back and forth in this moving liquid, like water plants swaying in a river current.

The strands, called hair cells, are suspended in a gelatinous substance called cupula, layered below a fluid called endolymph. When you jerk your head, the endolymph sloshed in one direction or the other through each canal, dragging the slower cupula with it and bending the embedded hair cells to and fro. The information about which way the hair cells are swaying at any given moment gets relayed to the brain via roughly 20,000 nerve fibres, and is interpreted by the brain as movement.

Now, when you spin in a circle, inertia causes the endolymph to slosh in a direction opposite to your head’s movement. It resists the movement of your head, dragging the cupula backwards with it and thus causing the sensory hairs suspended inside the cupula to bend against the direction in which you’re spinning. However, within moments, the endolymph (and thus the more gelatinous cupula) adjust to the movement of your head, and start going with the flow. This causes the hair cells to straighten, and your brain no longer receives the message that you’re spinning. Your perception has become normalized to the rotation of your head, giving you the sense that you are still, and the world around you is rotating.

Then, suddenly, you stop!

You have halted the rotation of you semicircular canals. But because of inertia, the endolymph keeps spinning, resisting change yet again. As the fluid continues to move, it once again deflects the cupula - this time in the direction in which you were spinning moments before - and as the oozing cupula bends those hair cells, a signal of movement is transmitted to the brain. You sense that you are moving but you’re not. That’s dizziness.

Whoa! That was a lot to take in. Although most of my posts cater to the general public, this one might be mind-twisting for some of you. Take your time and go through it. Visualize stuff. This is the start of knowledge (trust me, it gets better, till you end up buried in thousands of technical academic papers for completing your PhD ).

P.S. Physics people, the first para of the answer was a joke. But seriously, stop undermining other disciplines! To understand the beauty of biology from the eyes of a physicist, read What is Life? by Erwin Schrodinger.