In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck.
The bone is named for Atlas of Greek mythology, for just as Atlas bore the weight of the heavens, the first cervical vertebra supports the head. However, the term atlas was first used by the ancient Romans for the seventh cervical vertebra (C7) due its suitability for supporting burdens. In Greek mythology, Atlas was condemned to bear the weight of the heavens as punishment for rebelling against Zeus. Ancient depictions of Atlas show the globe of the heavens resting at the base of his neck, on C7. Sometime around 1522, anatomists decided to call the first cervical vertebra the atlas. Scholars believe that by switching the designation atlas from the seventh to the first cervical vertebra Renaissance anatomists were commenting that the point of man’s burden had shifted from his shoulders to his head--that man’s true burden was not a physical load, but rather, his mind.
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 atlanto-occipital joint allows the head to nod up and down on the vertebral column. The dens acts as a pivot that allows the atlas and attached head to rotate on the axis, side to side.
The atlas's chief peculiarity is that it has no body. It is ring-like and consists of an anterior and a posterior arch and two lateral masses.
The atlas and axis are important neurologically because the brainstem extends down to the axis.
The anterior arch forms about one-fifth of the ring: its anterior surface is convex, and presents at its center the anterior tubercle for the attachment of the Longus colli muscles and the anterior longitudinal ligament; posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for articulation with the odontoid process (dens) of the axis.
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In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes.
The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bone: vertebrae separated by intervertebral discs. Individual vertebrae are named according to their region and position, and can be used as anatomical landmarks in order to guide procedures such as lumbar punctures.
The spinal column, a defining synapomorphy shared by nearly all vertebrates, is a moderately flexible series of vertebrae (: vertebra), each constituting a characteristic irregular bone whose complex structure is composed primarily of bone, and secondarily of hyaline cartilage. They show variation in the proportion contributed by these two tissue types; such variations correlate on one hand with the cerebral/caudal rank (i.e., location within the backbone), and on the other with phylogenetic differences among the vertebrate taxa.
Ce cours est une préparation intensive à l'examen d'entrée en 3ème année de Médecine. Les matières enseignées sont la morphologie macroscopique (anatomie) , microscopique (histologie) de la tête, du c
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