The first human cervical vertebra (atlas or C1) that articulates directly with the base of the skull. Injury to any of the neck vertebrae can be serious and may result in paraplegia or quadriplegia. The spine supports the head, holds the body upright, and protectively encircles the spinal cord which passes through its central cavity. The spine consists of 33 vertebrae, articulated by intervertebral discs which allow flexibility and movement.