The platysma muscle has several functions: - Tenses the skin of the neck - Pulls the lips and corners of the mouth downward - Aids in the depression of the mandible at the temporomandibular joint. Origin: The platysma is a thin muscle that merges with the fascia covering the deltoid and pectoralis major muscles. Insertion: The fibers of the platysma attach to the lower border of the mandible and the surrounding muscles, including the depressor anguli oris and depressor labii inferioris muscles.