Fig. 8. NMJ-capping cells are integral, plastic cellular components of the NMJ. (A) Relationship between four main cell types proposed to constitute the mammalian NMJ: muscle fibre, motor nerve terminal, terminal (perisynaptic) Schwann cell and NMJ-capping cells, named here `kranocytes' (see Discussion). (B) Stages in kranocyte reactivity to denervation, paralysis or muscle atrophy that could indicate a permissive function for these cells in terminal Schwann cell and axonal sprouting. Kranocyte sprouting is the first reaction, followed by terminal Schwann cell sprouting, then axonal sprouting.