The top bone of your neck, called the atlas or C1, is a very unique bone and many would consider the most important bone of your spine. Your head sits directly on top of your atlas, and you are able to nod your head because of the joint between your head and atlas. Additionally, you are able to rotate your head because of the type of joint that is found between the atlas ant the bone below it, C2 or axis. Your neck and spine line up below that based on how C-1 is positioned, making it important for the atlas to be positioned correctly, because the rest of the spine will follow suit, improving your posture and function.
There are many important structures that are directly affected by the position of the atlas bone. These include:
The C-1 and C-2 nerve roots, right at the back of your head at the base of the skull, lay directly above and below the atlas. They become extremely sensitive and swell when the atlas shifts out of normal position, leading to what is called a cervicogenic (neck caused) headache.
The vertebral arteries on each side make a number of 90 degree turns at the atlas before entering into the skull and feeding the majority of the brain. Misalignment at C1 can put pressure or stretch on those arteries and affect blood flow to the brain. (Migraine headaches are thought to be caused by spastic arteries within the brain and evidence has shown a correlation between misalignment of atlas and migraine headache severity and frequency.)
The muscles at the back of your head, into your neck, shoulders and even your low back can be affected by a misalignment of C1. Through postural reflexes, these muscles can become tight and painful in an attempt to compensate for the misalignment of your atlas, causing all kinds of problems from tension headaches to low back pain to sciatica.
The dura mater, the bag that contains the brain and spinal cord is attached to the skull, C1, and C2. With misalignment of the atlas, there is the potential to put tension on the dura. This can cause problems in the flow of cerebral spinal fluid (The "blood" of the brain.), resulting in pressure changes in and around the brain and spinal cord. It has been speculated that this is a cause for a myriad of conditions including all types of headaches, sinus problems, even low back pain through tension on what is called the lumbar cistern. Normalizing atlas alignment can relieve this tension, allowing for healing and relief.
The TMJ, or jaw joint, is typically less than ¾ of an inch from the atlas and is attached by soft tissue. Misalignment of the atlas can put pressure or tension on the TMJ altering its normal movement, causing symptoms in the jaw region.
The eustachian tubes, or ear canals, can be closed off due to tension in the upper neck when the atlas misaligns. This causes fluid to build up in the ear, leading to ear pain and potentially infections. Correction of an atlas misalignment can facilitate drainage and proper flow of the ear canals. This is why there is evidence that upper cervical chiropractic adjustments can be as effective as medical intervention for ear infections.
Lastly, a fun fact to leave you with. The atlas is named for the Greek god Atlas, who held the world on his shoulders, while your atlas holds up your whole world, which lives in your head. What better name for such an important bone?