Table of Contents

My Body in Space – Stepping Out

Sheet 1: The whirligig

Note

The following exercise should be performed on a voluntary basis only since dizziness and possible nausea may result. The educator or other responsible adult must be on hand to supervise and provide against any complications.

Contextual information for the educator:

Our brain gathers information about its environment through our eyes, muscles and tendons regardless of the orientation of our bodies. A set of sensors track the movement of the liquid in the canals of the inner ear. On Earth, even when our muscles are at rest, they are still subject to the effects of gravity. However, the energy required to perform movements is not always the same. Archimedes' principle states that a fluid buoys up a completely immersed solid by an amount equal to the weight of the fluid it displaces. Therefore, in water, moving our arms requires more energy than in the open air because of water resistance. Of course, air too causes some resistance. We need only think of the force we feel on our arm when we stick it out the window in a moving vehicle.

What happens to the body when it is in a state of weightlessness?

After an astronaut leaves Earth for the void of space, his or her brain continues to interpret their surroundings using the same visual cues as on Earth. These conflicting signals will impede the astronaut's ability to adapt to the new weightless environment. He or she is disoriented because their inner ear sensors and muscles are unable to orient themselves in weightlessness. The astronaut's brain relies solely on visual information.

Let's identify the sensors of the inner ear and determine their location. The sensors receive information depending on the position of the otoliths that move around inside the canals. Let's take a look at the configuration of the inner ear, which contains the organ of equilibrium.

The inner ear complex is made up of three semi-circular canals, each perpendicular to one another. These are filled with otoliths-crystals of sodium carbonate that move by gravitational force along the walls of the sensory cells. As a result, we perceive movement in all three dimensions. The inclination of the body moves the crystals and stimulates the sensory cells. As a result, a nerve impulse is sent to the brain, which computes the inclination. When our head turns, the otoliths move under their own weight and generate a nerve message.

In a weightless environment such as onboard the International Space Station, the nerve impulses are quite different from their Earth-bound state. The otoliths no longer stimulate the cells of the semi-circular canals as they do on Earth and so the astronaut's sense of balance is disturbed. Disturbances in equilibrium cause a feeling of falling or being upside down. This may result, in the short term, in a disorder called space sickness, which takes the form of dizziness and vomiting in the first days of exposure to weightlessness.

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