Neurobiology deals with the study of structure and functions of the nervous system. The brain is the most important organ of the nervous system, and it makes us human since it is the seat of our behaviour. Nerve cells (neurons) are the basic building blocks of the nervous system (or the brain) in the same way that elementary atomic particles and forces are the building blocks of physical matter. Neural function depends on the coordinated action of neurons. Therefore, the basic principles and mechanisms of neurophysiological functions from molecular, genomic to cellular-organismal levels form the central theme of the book. Mathematics has been used when considered essential; emphasis is given to the development of qualitative intuitive understanding of complex functions. For understanding the nervous system or the brain it is essential to learn how single cell and molecules in the nervous system function to produce electrical activity. Neuroelectric phenomena have thus been duly emphasized in the text. Pathological, pathophysiological aspects of neurobiological phenomena have also been fairly focused on.