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The atlas is the topmost vertebra and the axis (the vertebra below it) forms the joint connecting the skull and spine. The atlas and axis are specialized to allow a greater range of motion than normal vertebrae. They are responsible for the nodding and rotation movements of the head.
The atlas (C1) is the topmost vertebra, and along with the axis forms the joint connecting the skull and spine. It lacks a vertebral body, spinous process, and discs either superior or inferior to it.
In anatomy, the axis (from Latin axis, "axle") is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests. The spinal cord passes through the axis. The defining feature of the axis is its strong bony protrusion known as the dens, which rises from the superior aspect of the bone.
The atlanto-axial joint is a joint between the atlas bone and the axis bone, which are the first and second cervical vertebrae.It is a pivot joint that provides 40 to 70% of axial rotation of the head.
The head rests on the top part of the vertebral column, with the skull joining at C1 (the first cervical vertebra known as the atlas). The skeletal section of the head and neck forms the top part of the axial skeleton and is made up of the skull, hyoid bone, auditory ossicles, and cervical spine. The skull can be further subdivided into:
The atlas is a ring around the roughly cone-shaped extension of the axis (second cervical segment). The axis acts as a post around which the atlas can rotate, allowing the neck to swivel. There are 23 discs in the human spine: 6 in the neck region, 12 in the middle back region, and 5 in the lower back region. [3]
The anterior atlantoaxial ligament is a strong membrane, fixed above the lower border of the anterior arch of the atlas; below, to the front of the body of the axis. It is strengthened in the middle line by a rounded cord, which connects the tubercle on the anterior arch of the atlas to the body of the axis.
A typical vertebra has a body (vertebral body), also known as the centrumwhich consists of a large anterior middle portion, and a posterior vertebral arch, [2] also called a neural arch. [3] The body is composed of cancellous bone , which is the spongy type of osseous tissue , whose microanatomy has been specifically studied within the pedicle ...