serotonin and norepinephrine levels in the the brain are altered by drugs like prozac and zoloft. these are known as

for the points

that scientist would be robert hooke

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