**1. Introduction**

Cell signalling is arguably the most important area of modern biology. The subject encompasses the control of cellular events, especially in response to extracellular factors. It has been suggested that the human body is one of the most complex machines ever produced (Dawkins, 1989) and the regulation of the activities within it are also equally complex.

Interest in cell signalling does not simply stem from an academic viewpoint either. Certainly there is a vast resource of research which is focuses on the investigation of signalling pathways and the control which they bestow on a cell. However, there are tangible reasons to take an interest here too. The vast majority of new pharmaceutical compounds under development are aimed at the modulation of proteins involved in cell signalling events (Filmore, 2004). Such proteins may be G protein-coupled receptors (GPCRs) or perhaps kinases which are downstream of such receptors. Many anti-cancer studies are now focused on the development of compounds which modulate Mitogen Activated Protein Kinases (MAPKs) for example. Therefore, an understanding the working of the components of a signal transduction opens up avenues for the future modulation of such activities with the development of new therapies and pharmaceutical agents.

The study of cell signalling can seem very daunting. Vast diagrams full of acronyms can put off the most ardent reader, but there are many basic principles which underpin the subject. In cell signalling compounds are made and initiate a response, and this is true whether the molecule originates outside the cell or is created inside. The signal transduction pathway carries a "message", with such a message originating in one place, either outside of the cell, or from another part of the same cell, but having a response elsewhere. The keys to cell signalling are that the message needs to be conveyed in a specific manner, so that it is not scrambled and misconstrued and that the cell must be able in most cases to revert back to a state or activity in which it was engaged before the message arrived, that is, the signal transduction pathway needs to be stopped when the message is no longer needed to be conveyed.

Even though the principles are simple, it is still hard to understand the complexities of cell signalling. Often signalling events are over-simplified, and components are aligned in neat rows. However, a more holistic view shows that signalling is extremely complicated and hard to understand. There are many books and chapters which explain cell signalling (Hancock, 2003; Hancock, 2010; Krauss, 2008) but these are all based on the description of the science, with the molecular details often putting off the reader who may be new to the field. Therefore, often an analogy to explain such a complex subject would be very useful, and may offer a more attractive way to teach the subject and to engage those who seek a better understanding of the area of study. In this chapter music is used as an analogy to try to shed light on some of the events in cell signalling. It has already been suggested that the use of such an analogy will be useful to those trying to get to grips with the subject (Hancock, 2005; 2009) and this chapter will expand and elaborate on those ideas. It is suggested that this can be used by those studying and teaching cell signalling.
