If there is a superficial cut in the region of middle pa of posterior triangle of neck, patient will experience problem

Roof of posterior triangle is formed by the investing layer of deep cervical fascia.Accessory nerve lies just deep to the investing layer at the middle of the posterior border of sternocleidomastoid muscle and across the posterior triangle and reaches the anterior border of trapezius, which it supplies.Shrugging of shoulder is an action of trapezius.