The scalene muscle, which is divided into three sections: anterior, middle and posterior. The brachial plexus and the subclavian artery pass between the anterior and middle scalene which can cause thoracic outlet syndrome, carpal tunnel syndrome and other painful conditions through the neck, shoulders and arms. The scalenes are responsible for lateral flexion of the cervical spine and elevation of the ibs during inspiration which assists greatly in breathing with easy.
To stretch this muscle the stretcher is supine with their head and neck rotated to one side as far as it will go. Make sure the stretcher keeps their nose pointed to the ceiling and pull the opposite shoulder away from their head, lengthening the scalene to their pain free end range. The partner places their hand just above the stretchers ear and their other hand on the stretchers shoulder to anchor it. The stretcher should then attempt to push against the partners hand, making sure they do not rotate their head whilst doing this. Also make sure the stretcher does not lift their shoulder. After this stretch the stretcher should relax and inhale deeply. On the exhale the stretcher should try to extend their neck further, once again making sure their nose is pointed to the ceiling.
Stretching the muscle through the neck and shoulders can relieve the tightness but if done to aggressively can cause pain. The upper trapezius is responsible in elevating the shoulder and flexion of the neck and head. This stretch is designed to improve the range of motion in cervical rotation and flexion and shoulder depression.
To do this particular stretch the stretcher must lay on their back and rotate their head as far to the right as they can. The partner places their hand on the side of the stretchers head and on the stretchers shoulder. The stretcher then tries to push against the partners hands as if pushing their neck and shoulder together. The stretcher then relaxes and breathes in deeply, on the exhale the stretcher rotates their head further away from their shoulder and deepens the stretch.
When doing this stretch be very mindful that this is your posterior neck we are talking about, this is your spine and the muscles surrounding it. If you feel something is wrong and you should stop, then stop. Other than that, keep your arms and shoulders relaxed and by your side. Position your feet evenly and about shoulder length apart, like all stretches to create an even and steady base. Don't rotate you head either way, make sure it drops onto your chest straight.
Images taken from "Upper Body Stretches" wall chart by B. Walker.