What extra point is located at the back of the neck, 2 cun superior from below the spinous process of C7, and 1 cun lateral to the midline?

The extra point located at the back of the neck, specifically 2 cun superior to the spinous process of C7 and 1 cun lateral to the midline, is known as Bai Lao. This point is traditionally used in acupuncture and herbal medicine for several purposes, including the treatment of respiratory conditions, cough, and throat issues. Bai Lao is also recognized for its role in alleviating symptoms related to stress and anxiety.

The specific anatomical location of Bai Lao is significant for practitioners, as it is positioned in a region of the nape of the neck that can impact the flow of Qi and blood associated with both the head and the upper body. This makes it clinically relevant when addressing a variety of conditions that originate or manifest in these areas, further solidifying its designation as an extra point in traditional Chinese medicine.

The other points listed do not share the exact anatomical description provided in the question. For instance, Bi Tong is typically used for nasal issues, Jia Cheng Jiang is related to the jaw area, and Er Jian pertains to the ear region, thereby excluding them from being the correct answer in this context.