Nerve cell structures (7)
I believe the answer is:
ganglia
'nerve cell structures' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ganglia that I've seen before include "Concentrations of strength" , "Swellings on a nerve fibre -- gala gin (anag)" , "I nag gal, having group of nerve cells" , "Cellular networks" , "Nerve cells radiate from these" .)