13. What happens within the sarcomere to make a muscle contract? Draw and use the following: actin, myosin, crossbridge, calcium, troponin, and tropomyosin. How does that relate to the phrase "sliding
filament theory?"

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;

stimulus is a change in the environment that causes an organism to react. the response is the reaction to the stimulus. some examples of stimuli for zebras are drought, to many predators, and bad feeding grounds such as dead grass or plants. zebras respond to stimuli just like all other living organisms