Before we can begin to discuss the various types of hormones, how they are formed, how they are secreted, how they act upon the body, and then how they can possibly influence behaviour, it is first necessary to provide a brief background to some basic psychobiological concepts. In this chapter I will describe the general layout of the nervous system, and explain how cells within the body (and especially within the central nervous system) communicate with one another.

Neuroanatomical directions

Neuroanatomists have devised a three-dimensional system of directional coordinates in order to navigate around the complex machinery of the brain. Instead of terms like ‘front’ and ‘back’ or ‘top’ and ‘bottom’, which are all relative, they instead employ the following terms that are always taken from the orientation of the spinal cord. There are three main axes: anterior – posterior, dorsal–ventral and medial–lateral. Thus, in most vertebrates that walk on four legs, the front (towards the nose) is called the ‘anterior’ while the back (towards the tail) is called the ‘posterior’, though when referring to the brain the terms ‘rostral’ (towards the front) and ‘caudal’ (towards the tail) are often used. Towards the surface of the back is referred to as ‘dorsal’ (think of a shark's dorsal fin) while the aspect towards the chest/stomach is referred to as ‘ventral’. Towards the sides is ‘lateral’ while towards the middle is ‘medial’.