The trapezius muscle is a large diamond shaped muscle in your upper and middle back and neck. It it responsible for both shoulder and neck movements. Trigger points in the upper portion of this muscle are the most common points to develop in the body. These trigger points most often occur due to poor posture, such as a slumped sitting posture. Trigger points in the upper portion of the traps will cause pain to refer into the neck, head, and into the temple. These points are one of the most common causes of headaches.