In 2007, researchers at the University of CaliforniaâDavis determined that our Solar System was fully formed at 4.568 billion years ago. They did this by determining the age of stony materials from the asteroid belt.
When to see a doctor. See your doctor immediately if you experience the signs and symptoms of migraine with aura, such as temporary vision loss or floating spots or zigzag lines in your field of vision. Your doctor will need to rule out more-serious conditions, such as a stroke or retinal tear.
In other words, contraction of radial smooth muscle causes dilation of the pupil. This explains the autonomic actions: 1  Increased release of acetylcholine by the parasympathetic nervous system causes contraction of circular smooth muscle. 2  This makes the pupil (the dark hole) smaller.he pupil is contricted or dilated by the contraction of smooth muscle in the iris. There are two types. One type is arranged in the circle near the pupil. When a circle of muscle contracts, the circle becomes smaller. Thus contraction of the circular muscle causes constriction of the pupil.