The Cranium is the part of the skull that encloses and protects the brain within the cranial cavity. The cranium is formed by several bones that are fused and fixed together. These bones have a number of holes in them which allow the cranial nerves and various blood vessels to pass through on their way to the rest of the body.
The largest of these holes is the foramen magnum in the occipital bone at the base of the cranium, which allows the brainstem to connect with the spinal cord. The occipital bone is the point where the skull balances on the top vertebra the atlas, at the atlanto occipital joint. The shape of the atlas, which is like a ring, allows the skull to make small nodding movements which do not involve the whole of the neck. Turning movements of the head take place lower down, in the joint between the atlas and the second vertebra, the axis.
The balance of the skull and the capacity to make these movements help to fine tune our poise and co-ordination; functions that works best when the numerous small muscles that connect the skull to the neck are maintained in a free and flexible condition. If these muscles are held rigidly or are constantly being over-used, this can interfere with the balance and functioning of the rest of the body. Working to maintain the freedom of the atlanto occipital joint is central to the Alexander Technique, in which pupils learn to avoid tightening and contracting here, so that the head can balance freely on top of the neck during activity and at rest, as it is designed to.