This interrupted case study follows "Elaina Lee" and her family through a series of medical mishaps. Elaina suffers a reaction to an overdose of an herbal remedy prescribed to her while studying abroad in Africa. Upon returning home, she feels unwell and has a mild seizure. Her brother, who stays with her overnight in the hospital, awakens to find that he cannot move his legs. The common thread between these two patients is an abnormal level of potassium in the extracellular fluid (hypokalemia and hyperkalemia). Students are given signs, symptoms, and medical data. The goal is to construct links between extracellular potassium concentration, resting membrane potential, and action potential activity while also considering the effect of various hormones on Na/K-ATPase pump activity. Originally developed for a one-semester animal physiology course taken by sophomore and junior science majors, this case study could also be used in general biology if the Nernst equation, used to calculate the equilibrium potential for potassium, is covered in this course.