How does gravity’s force first act on the human body?
The human body is adapted to life on Earth. One factor that the human body has adapted to is gravity. We don’t realize it, but we use these senses everyday in keeping balance and having a sense of direction. However, most of these senses react differently in space and confuse the brain. In space, the force of gravity is actually still present, but slightly diminished. When in orbit, everything is in free-fall, which creates the feeling of weightlessness. This lesser gravity is called microgravity.
Our brains use visual cues, the proprioceptive apparatus, and the vestibular apparatus. The proprioceptive apparatus is made up of the mechanical receptors in the muscles, tendons and joints and some pressure receptors on the skin, mostly on the bottom of the feet. The vestibular apparatus is made up of two important parts; the semicircular canals and the otolith organs. In space, these senses confuse the brain, rendering only the eyes as useful. One astronaut said that he felt that he had flipped 180 degrees immediately as the main engines cut off. These illusions can continue for even a couple of days after entering space.
-- The inner ear is affected during space travel because of the effects of microgravity.
The confusion of these senses as well as the motor activity needed to keep the head upright causes motion sickness. The symptoms are similar to motion sickness on earth. This only lasts for the first three days space flight, but a similar feeling comes at the end of long flights.
-- When astronauts are in space they don't have any sense of direction.
Although weightlessness seems to be a lot of fun, some of the physical side effects might not be. One study involved women lying in bed for 50 days in a row at with their feet at a six degree angle from their heads. This simulated the effects that weightlessness has on the human body. Fluids fill the upper portion of your body, causing the face to swell. When floating, there is less strain on weight-bearing muscles. This causes a loss of up to three percent muscle mass a week in certain areas of the leg. Bone mass in the lower body can drop two percent a month.
In space, people are in constant free fall towards earth. However, the difference from skydiving is that the forward velocity of the spacecraft keeps it in orbit. This is why people in space don’t feel like they are falling.
Written By: Alvin