The muscles on either side of the neck are the sternocleidomastoid muscles, whose main function is to tilt the head and neck to the same side and turn them to the opposite side when one side of the muscle is contracted, and to tilt the head back when the muscles are contracted bilaterally. The sternocleidomastoid muscle has two starting points, the sternal head starts in front of the sternal handle, and the clavicular head starts at the sternal end of the clavicle. The deeper layers of the sternocleidomastoid muscle are lined with a variety of important tissues such as the vagus nerve, the parasympathetic nerve, and the cervical plexus nerve. The muscle is mainly innervated by the parasympathetic nerve as well as by the anterior branch of the 2nd to 3rd cervical nerves. When the sternocleidomastoid muscle is injured, neck pain and limited movement will occur, often accompanied by muscle spasm, muscle stiffness and other symptoms, and in severe cases, dizziness and headache, tinnitus and even vertigo and other symptoms.