The driving age should be raised up to 18 because teens can be a little careless. Driving at the age of 18 is a more mature age for teens because they can have more responsibility. Teens should not be driving at the age of 16 because they could be texting and driving or drinking and driving with some friends.
During contraction, the smooth-muscle cell's intermediate filaments help to draw the cell up, like closing a drawstring purse. Calcium ions regulate contraction in smooth muscle, but they do it in a slightly different way than in skeletal muscle: Calcium ions come from outside of the cell. Calcium ions bind to an enzyme complex on myosin, called calmodulin-myosin light chain kinase.
Some examples of smooth muscles are the ones in our digestive system, that relax and tighten to control the movement of food through our body. Another example is the muscles in our bladder that (when relaxed) allow storage of urine and (when contracted) push the urine out of our body.