The diagram shows the different kinds of electrical potentials that can occur across the cell membrane of nerve cells. These are presented as if they have been classified; thus, e.g. there are three kinds of autogenic potentials - miniature, sawtooth and sinusoidal - which are all spontaneous variations in potential and which differ in the pattern of this variation with time.
Lines with arrow-heads indicate that a suffcient level of one potential may cause the other to occur; thus, e.g. if a local potential is sufficiently depolarising to reach the threshold (at the axon hillock) then a spike (action potential) will occur.
Plus (+) and minus (-) signify hyperpolarising and depolarising changes
in the membrane potential, i.e. increasing or decreasing it.