My main motivation for writing this book stemmed mainly from my teaching experience in neurophysiology. For more than 30 years as a professor it became clear that students of the first semesters of Medicine, Nursing, Physiotherapy, Dentistry, Psychology and others had substantially forgotten elementary concepts that should have been learned in high school. Concepts such as atom, molecule or Coulomb's law seem stored in the neuronal "trunk” of memories but the key that opens this source of information had been lost. For students who decide to pursue a career in any of these fields, this is elementary knowledge and the lack of it thereof poses a serious problem. The nervous system is made up neurons very much like the elementary units or bricks needed for a building. However, the functioning of such units is based on electric currents and movement of chemical substances. This indicates that to really understand how neurons work, it is necessary to understand what Ohm’s law is, how an electric current behaves in an aqueous medium, what the physical principles of the diffusion of solutes are, etc. Then, the purpose of this book is to guide students (and the professor, who is generally not a physiologist) towards a real understanding of how the "bricks" of the nervous system work, that is, how nerve cells are polarized, activated or inhibited, how they conduct their electrical signals, how they communicate with each other, and what interactions can occur in neuronal arrangements. The clear understanding of a concept from the start helps to understand subsequent concepts in a scaffolding manner as presented in this book. This is a book aimed essentially at undergraduate students. However, I believe that it can also be of great help for graduate students in clinical areas or beginners in any other biomedical research discipline. Special emphasis has been placed on using simple language, albeit with due academic rigor. Unfortunately, the neurophysiology books that are currently in libraries lack the explanation of these elementary phenomena in detail. Without a doubt, having a book with the characteristics mentioned before and that is also educational, compact, affordable, and available in digital format is particularly convenient for students and teachers at biomedical schools and faculties around the world.