Fiber arrangements of cutaneous and muscular rami in cervical nerves of the rat--regarding conception of the spinal nerve stratum-structure.

Fluorescence tracers DiO and DiI were applied to compare fiber arrangements of cutaneous and muscular rami in the proximal region of anterior and posterior branches of cervical nerves. Results show that a ventrodorsal relationship of cervical nerves is observed in gross level; however, fiber arrangements of cutaneous and muscular rami differ in anterior branches according to distance from the anterior root and dorsal root ganglia. That is, the fibers have a scattering course (no ventrodorsal relationship) in distal regions. Moreover, just before entering anterior roots, the motor fibers of muscular ramus run through the ventral part and sensory fibers of muscles and fibers of cutaneous ramus run through the dorsal part and intersect with motor fibers of the posterior muscular ramus. In contrast with the anterior one, in posterior branches of cervical nerves, cutaneous and muscular rami fibers are very regularly arranged in the distal and proximal region. Based on these results, the ventrodorsal relationship of fiber arrangements could exist in posterior branches and proximal region of anterior branches. Present results differ with those of the spinal nerve stratum-structure; therefore, they are insufficient to elucidate the relationship of peripheral nerves by conception of spinal nerve stratum-structure.