A<unk>  is the segment of spinal cord to which a given pair of dorsal and ventral roots is attached. Because the adult spinal cord does not extend down as far as the vertebral column does, the lower<unk> s are not opposite their correspondingly numbered vertebrae. Thus<unk>  S1 is opposite the T12 vertebra.
Myelomere
Dendrosome
Neuromere
Nuclear bag fiber
Endosome
Nucleus 
Myelin
Microvesicles