|Image of the CNS of Lymnaea dissected out by
Richard Mands This is pinned out onto sylgard
Like all multicellular animals, the behaviour is predominately controlled by the central nervous system, or CNS. In snails, this is made up of about 7 ganglia, which contain 4000-100000 individual cells, often called neurons. Here is a high magnification view showing some of the neurons in sharper focus
The ganglia are connected together, and to the muscles and sense cells by nerves, which contain several thousand axons.
Snails are very good for analysis of nerve activity and interactions, because the cells bodies are large and, in some species, like Lymnaea stagnalis, colored in slightly different shades of orange.
Workers in Sussex, York, Preston and Manchester have mapped many of these cells, and find that each snail is built to the same pattern. Maps of some of the best studied neurons are available here.
|Typical molluscan neurons have a call body near the edge of the ganglion, making it easy to locate them. This gives rise to an axon, which runs out of a nerve or to another part of the brain. The axon often has branches, sometimes called neurites or dendrites, which provide the site of contact with other neurons. Click the picture to see a movie of the VD1 neuron, seen in different planes of focus. (Neuron filled with a fluorescent dye Lucifer yellow, by Ian Rotherham)|