How do the cervical plexus and the spinal accessory nerve contribute to the innervation of the trapezius muscle? As seen from within using Sihler's stain

Objective: To determine how the spinal accessory nerve and the trapezius; b ranches of the cervical plexus contribute to the innervation of each of the 3 parts of the trapezius muscle. Special emphasis was placed on the nerve supply of the clinically most important descending part of the muscle. Design: Anatomical analysis of the distribution of the cervical plexus and spinal accessory nerve branches in the human trapezius muscle. Materials: Twenty-two trapezius muscles from 11 perfusion-fixed human cadav ers ranging in age from 66 to 92 years (mean, 81.7 years). Interventions: The specimens were dissected free and macerated, decalcified , and stained according to Sihler's technique for about 6 weeks. The transl ucent, stained muscles were then backlit, and the findings were documented photographically and by schematic drawings. Results: In all 22 muscles, the innervation of each of the 3 parts of the t rapezius muscle was seen. In all muscles investigated, the nerve supply to the descending part of the muscle consisted of a single fine branch of the spinal accessory nerve, whereas the transverse and ascending parts were inn ervated by both the spinal accessory nerve and the trapezius branches of th e cervical plexus. Conclusion: Our results, especially those involving the descending part of the trapezius muscle, may help to minimize the rate of unexpected trapezius muscle paresis after surgery of the neck.