Central relationships of trigeminal and cervical primary afferents in the spinal cord and medulla

The structural relationships between primary trigeminal and cervical dorsal root afferents in the spinal cord and the medulla were investigated in 13 cats. In 5 cats rhizotomies of one upper cervical dorsal root and of the contralateral trigeminal dorsal root were done at one operative session. In the remaining 8 cats rhizotomies of from 1 to 3 cervical roots were performed. The resultant degeneration was studied by the Nauta-Gygax and Fink-Heimer methods. The degree of anatomical overlap between afferents of the first 3 upper cervical roots and trigeminal terminals in the dorsal horn at identical levels is maximal in the lower half of C1 and upper third of C2. Minimal overlap of C4 with trigeminal endings occurs, while no afferents from the C5 to C8 roots reach the caudalmost endings of the trigeminal. Convergence of cervical with trigeminal afferents is also seen in the spinal nucleus of V in the low medulla in two discrete loci.