In the first chapter I explained how cells within the CNS communicate with one another. At first glance it seems that neural signalling and endocrine signalling are quite different from one another. According to Rosenzweig et al.(2002) there are four key differences:

1. 1 While neural communication is typically between fixed channels to precise destinations, hormonal signalling is rather more diffuse, as most hormones do not act immediately on localised areas but coordinate long-term changes in diverse regions of the body.

2. 2 Whereas neural messages are very rapid (occurring over milliseconds), hormonal communication is slower and is measured in seconds and minutes.

3. 3 Most neural messages are digitised, i.e. they either act or they do not (‘all or none rule’). Hormonal signalling is analogue, i.e. graded in strength: the more of a hormone that is released, the larger the effect.

4. 4 Some neural communication is under voluntary control while hormone release is not.

However, despite these differences, there are several similarities between hormonal and neural communication systems:

1. 1 Neurons and endocrine glands produce chemicals, which are stored for later release.

2. 2 Neurons and endocrine glands are both stimulated to release their chemicals.

3. 3 There are many different neurotransmitters and hormones, each with specific functions. Indeed some chemicals serve exactly the same function, e.g. norepinephrine and epinephrine are both neurotransmitters and hormones.

4. 4 Neurotransmitters and hormones react with specific receptor molecules at the postsynaptic receptor or at the target cell respectively.

5. […]