Nerve supply to platysma is:

The platysma muscle is the most superficial muscle of the neck. Unlike most skeletal muscles, the platysma is located in the superficial fascia . The muscle extends superiorly from the inferior border of the mandible and inferiorly to the clavicle to the fascia of the anterior shoulder and thorax. The platysma muscle is a muscle of facial expression and therefore is innervated by the facial nerve (cervical branch of CN VII). Ref: Moon D.A., Foreman K.B., Albeine K.H. (2011). Chapter 25. Overview of the Neck. In D.A. Moon, K.B. Foreman, K.H. Albeine (Eds), The Big Picture: Gross Anatomy.