Smooth muscle is present throughout the entire tracheobronchial tree. Bronchial smooth muscle tone is regulated by the vagus nerve, which, when stimulated, causes constriction (bronchospasm), and by the sympathetic nervous system, which produces dilation (bronchodilation).
The answer is <em>stratosphere.</em>
Digestion begins in the mouth. Saliva contains enzymes which begin to break down food. The mouth also uses the teeth and jaw to mechanically break down food.
There must be an abundance of food space and water or a lack of predators
