The Back of the Neck muscles run from the base of the skull to the back of the neck or even to the shoulder blades.
These muscles include some larger muscles such as Trapezius and Levator Scapulae; to many smaller deeper muscles such as Rectus Capitis.
A head forward posture can cause these muscles to become tight. A head forward posture is common in today's society due to sitting for extended periods in a slumped position.
The video shows a few great methods for stretching the muscles at the back of the neck.
For best results hold the stretches for at least 30 seconds, Repeat several times daily.