It is now over 200 years since Theodore Schwann first described
the cell which bears his name. Such early descriptions of nervous
system components were done without the powerful microscopes
we have today, yet Schwann and Ramon Y. Cajal made foundation
observations which still stand. Cajal’s papers, especially, show the
power of careful observation, an essential element of good science.
The Schwann cell has been historically underrated and poorly
understood. In particular, the myelin-forming Schwann cells or their
myelin are still often referred to as a simple ‘sheath’ for the neuron.
However, Schwann cells in all their complexity form essential partnerships
with neurons, and muscles. This is of particular relevance in
the case of the myelin-forming Schwann cell, an enormous cell that
expresses unique molecules and complex relationships related to maintenance
of the compact and non-compact myelin regions of its plasma
membrane. Schwann cells have other complex interactions, not least of
which are found where nerve terminals and muscle fibres form the
tripartite synapse in association with the perisynaptic Schwann cells.
There are also the poorly understood satellite cells that surround the
dorsal root ganglion nerve cell bodies, and of course the complexity of
non-myelinated Schwann cells and their axonal associations.