Trachea into left and right main bronchi. The trachea begins level with the sixth cervical vertebra and the carina is found at the level of the fifth thoracic vertebra (T5), opposite the sternal angle and can be positioned up to two vertebrae lower or higher, depending on breathing. The trachea is surrounded by rings of hyaline cartilage; these rings are incomplete and C-shaped. The cricoid cartilage is attached to the first tracheal ring at top of the trachea and acts as the bottom of the larynx. There are fifteen to twenty rings in total, separated by narrow intervals. These reinforce the
Effect of spaceflight on the human body of motion sickness for the first three days of travel due to the conflict between what the body expects and what the body actually perceives. Over time however the brain adapts and although these illusions can still occur, most astronauts begin to see "down" as where the feet are. People returning to Earth after extended weightless periods have to readjust to the force of gravity and may have problems standing up, focusing their gaze, walking and turning. This is just an initial problem, as they recover these abilities quickly. NASA jokingly measures SAS using the "Garn scale", named for United