From membrane excitability to metazoan psychology

•We point out that neuronal excitability is due exclusively to cation influx.•We argue that excitability is a brief disturbance of the normally alkaline cytoplasm.•The transient loss of cellular homeostasis underlies the ‘sentience’ of neurons.•All of metazoan psychology is a direct consequence of excitable cell activity.•The field of ‘consciousness studies’ should be built upon modern neurophysiology.

Unlike the nonexcitable cell membranes that are ubiquitous in all domains of life, excitable membranes are found almost exclusively in animal organisms (Protozoa and Metazoa). Their transient permeability to ion flow makes possible the rapid detection of, and response to, external stimuli, and results in the phenomena that most clearly distinguish fauna from flora: perception, cognition, and motor activity. Interestingly, all known forms of membrane excitability are a consequence of one unique mechanism: the influx of positively charged ions into the normally alkaline cytoplasm. Here, we suggest that the sudden reversal of the membrane potential during the sensory potential and the action potential is an electrostatic disturbance of homeostasis that is the necessary first step in the processes of ‘sentience’ and ‘irritability’.