The base of the skull near the ear (mastoid process)
The collar bone (clavicle) and the breast bone (sternum)
You have one on both sides of the neck. When acting individually, they will cause rotation of the head to the opposite side and side bending to the same side. When acting together they cause neck extension and protraction or a chin jutting forward appearance.
In the picture on the left you can see the “X’s.” These mark the areas where trigger points can be located. The red stippled area is the area where pain can be referred and felt. This muscle can cause headaches, jaw pain, and eye pain in addition to neck pain.
This muscle is very commonly associated with a whiplash type injury. In addition, working at a computer for many hours a day can lead to a dysfunction that involves the SCM. You can easily access this muscle by turning your head to the left and feeling the muscle pop out on the right. Same goes for the opposite side. Explore up and down the muscle, squeezing gently and feeling for uncomfortable spots. If you feel some restrictions or pain, it may be worth a trip to the office!