[Solved] The majority of the world's population resides in rural (nonurban)areas. Amygdala: A section of the brain that is responsible for detecting fear and preparing for emergency events. Medulla: the base of the brainstem; controls heartbeat and breathing. Erotic Plasticity: Refers to the degree to which an individual's sex drive can be changed by societal or situational factors. Refractory Periods: The period immediately following an action potential during which a neuron is incapable of activating a second action potential, ensuring that signals are sent in only one direction.