Where some people consider a neuron the most simple building block available in constructing a network (it either fires or doesn't and it can be influenced with chemicals), each cell in our body is actually an agent by itself which on a lower level has very intricate capabilities and behaviours. A cell in itself could in a way be considered an organism, even though a human has many of those and they are interrelated.
In order to follow my drift, you should look up the article on the definition of a cell in biology: Wikipedia link
Each cell is at least somewhat self-contained and self-maintaining: it can take in nutrients, convert these nutrients into energy, carry out specialized functions, and reproduce as necessary. Each cell stores its own set of instructions for carrying out each of these activities.
Cell surface membranes also contain receptor proteins that allow cells to detect external signalling molecules such as hormones.Or... each cell has the ability to sustain itself, has its own behavior and purpose and follows a set of simpler rules than the entire organism. Cells can generally multiply, although this depends on the type of cell. The more complicated a cell is, the less its capability to multiply. Some cells are said not to be able to multiply at all (neurons), although other research has indicated that this is not entirely the case.
Cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities. This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps: transcription and translation.Proteins have very complicated structures and may contain specific receptors, such that certain proteins may react to chemicals in the environment. This reaction may trigger a certain kind of behavior, thereby serving a particular purpose. For example, liver cells may give off chemicals to indicate to the body that there's a falling level of nutrients, thereby causing a desire to eat:
The chemical is released by receptors (protein molecules):
In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling (or "signal") molecule may attach.So, each cell in this system has a very specific function. It monitors levels of hormones or sugar (type of molecules) and the entire functioning of the organism basically is the recognition of signatures of a certain complex molecule, generally proteins.
The proteins are specified by DNA. The DNA is a large blueprint, which on being split results in a template (RNA), which then reconstructs DNA from that point. Unfortunately, during this templating process, it is possible that certain "errors" occur, which are basically mutations of the original DNA. You've started with a DNA signature that is the result of the merger of two cells of your father and mother. Through that set and in your lifetime, the cells in different parts of your body re-uses that DNA signature to renew and recreate other cells. The older you get, the more likely it becomes that one cell multiplication leads to a certain kind of errors that give a cell a potential fatalistic behaviour: cancer. The cell basically becomes rogue in that it starts to multiply quickly, thereby breaking some rules in the aggregate system. It develops a lump of some sort. When the cell also develops the ability to move (which some cells do and others don't), things become dangerous, since the cells that bear DNA where the cell multiplies at a very high rate move to other parts of the body.
Thus... in short... considering a neuron as a cell that fires and as the lowest important building block of a neural network is a grave mistake. Each cell itself has very, very complicated workings, reactions and behaviours that are each in itself very important, as these define the simple rules of the behaviour of the cell. If the cell has behaviour which may change over time or be heavily influenced by changes in the environment, we cannot assume that ignoring that effect in a 100-billion neural network will not make any difference as opposed to the view where it's considered of the utmost importance to understand and model them.
In previous posts (important numbers and statements), I've done some calculations on the memory requirements for a human brain. The result is that, assuming 4 bytes per neuron and connection, you'd need 400 Terabyte (400,000 Gigabyte) of memory in order to store all the connections and neuronal information.
Now... each neuron is a complicated cell, which through changes in its immediate environments or differing levels of chemicals, could slightly modify its behaviour. It could start to fire more often or fire less. Thus, in the simplest form for a model, each neuron would need to have a threshold modifier, which is influenced by another system, to regulate its individual responsiveness.
If we take into account that besides the processing of signals, the brain also responds strongly to chemical changes brought about by external factors, such as fear or emotions, then one could say that "emotive neurons" are those neurons that give off proteins of a certain type on the recognition of danger, causing other neurons to become much more responsive in their processing of signals. The exact level of chemicals produced is dependent on the number of cells that would produce a certain chemical and how strongly they produce it. Since this also depends on learning, the question remains whether the producer learns to produce less or whether the signal processors inhibit the signal more as soon as it is observed.
Thus... there may be three very complicated effects at work in the human brain, relating to consciousness and our efficiency of acting in our environment. We have the neuron cells, which I see as pattern recognizers, which also learn and where sub-assemblies of neurons work together to create a learning experience (process signal, recognize situation, provide stimulus to react to situation, verify effectivity of reaction, reduce/increase stimulus).
And the glial cells, which outnumber neurons by a factor 10, but which have so far not been researched in great detail. Could it be that there's a secret in the interaction of neurons + chemicals and the glials that together, as three complicated systems, produce that which we call "consciousness"?