Myelin sheath

Nerves are protected by layer of connective tissue: the nerve sheath or myelin sheath. Connective tissue is normally controlled from the new mesoderm and has a decrease of cells in the CA phase.
In myelin sheaths, however, cells are built up in the CA phase like any old mesodermal program.
In the healing phase the extra cells stay in place, like in any new mesodermal program.
The program of the myelin sheaths is a "mesodermal mix".

Because nerves are involved, this program is related with the periosteum, a network of nerves and blood vessels around the bones. Evolutionary, the periosteum is controlled by the oldest part of the ectoderm, the post-sensory cortex and its function is  "feeling the contact" (see sensitivity patterns). The fifth sense, the sense of feeling, was added.

It seems that when the mesoderm arose, an excruciatingly painful blow could be compensated by the (partial) "pinching off" nerves by the extra myelin sheath cells.

Whether it involves the left or right side of the body depends on biological laterality.

Theme

Touch conflict. Not wanting to feel the contact, not wanting to feel the blow, not wanting to be touched.

CA phase

Cell increase in the myelin sheath, proliferation of the nerve sheath, thickening of the myelin sheath in the affected body part.

Biological purpose

Blocking the pain, not feeling it or it being less severe.
Because of the improved insulation, information from the unwanted pain is less or not transmitted to the brain.

Symptoms

Neurofibroma, neurofibromatosis, Recklinghausen's disease.

PCL phase

Functional normalization, the extra cells stay in place. 

At the end of the PCL-B the sensitivity returns to normal.