Let me first explain the anatomy behind this research. The rectus capitis posterior major muscle (RCPM for short) is a muscle located in the occipital triangle or at the base of your skull at the top of your neck (see picture). The action of the RCPM muscle is to extend the head (like your looking up at the ceiling) and to rotate the head at one of the superior-most joints of the neck: the atlanto-occipital joint.
The dura mater that this muscle has been found to be connected to is a layer of what is called the meninges. The meninges are known as the coverings for the central nervous system aka the brain and spinal cord, and are made up of 3 layers: the dura mater, the arachnoid mater (named for it's web-like connections to it's adjacent meninges layers) and the pia mater that is directly attached to both the brain and spinal cord (see picture). The dura mater is aptly named because of it's toughness and the need to cut through this layer in order to visualize the contents below.
Now that, hopefully, everyone understands the anatomy let me move on to the significance of this discovery, if you haven't already put two and two together. The connection between the RCPM muscle and dura mater is EXTREMELY signifigant. If the RCPM muscle is in spasm, like it usually is in those with tension headaches, it will pull on the dura mater directly effecting the nervous system! Of course, further research needs to be provoked from this study on how much tension, etc is placed and how much muscle contraction is needed to add tension, etc but this anatomical discovery is astonishing and adds to the great body of knowledge and to the future of research.