[not in handout, see intranet]
Human Brain
1012 neurons


Aplysia Brain
2 x 104 neurons


The human brain has roughly 1012 neurons (a million million) whereas the Aplysia californica nervous system contains only 2 x 104 nerve cells (twenty thousand). Aplysia neurons are clustered together in 5 pairs of ganglia, each ganglion containing roughly 2,000 nerve cells.