Sources of innervation of the neuromuscular spindles in sternomastoid and trapezius

The sources of innervation of neuromuscular spindles in sternomastoid and trapezius have been investigated in rats and mice, by degeneration experiments. The entire motor supply, both extrafusal and intrafusal, to both muscles, was from the spinal accessory nerve. The sensory supply to the spindles in sternomastoid and rostral trapezius was from cervical spinal nerves, and to those in the caudal trapezius was from thoracic spinal nerves.