Atlas (anatomy)
Information about Atlas (anatomy)
| Bone: Atlas (anatomy) | ||
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| First cervical vertebra, or Atlas | ||
| Posterior atlantoöccipital membrane and atlantoaxial ligament. (Atlas visible at center.) | ||
| subject #21 99 | ||
| Dorlands/Elsevier | a_70/12167134 | |
It is named for the Atlas of mythology, because it supports the globe of the head.
The atlas is the topmost vertebra, and – along with the Axis – forms the joint connecting the skull and spine. The atlas and axis are specialized to allow a greater range of motion than normal vertebrae.
The Atlas' chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra (the Axis). Its other peculiarities are that it has no spinous process, is ring-like, and consists of an anterior and a posterior arch and two lateral masses.
Anterior arch
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.The upper and lower borders respectively give attachment to the anterior atlantooccipital membrane and the anterior atlantoaxial ligament; the former connects it with the occipital bone above, and the latter with the axis below.
Posterior arch
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Median sagittal section through the occipital bone and first three cervical vertebræ, showing ligamentous attachments.
The posterior arch forms about two-fifths of the circumference of the ring: it ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the Recti capitis posteriores minores and the ligamentum nuchae.
The diminutive size of this process prevents any interference with the movements between the atlas and the skull.
The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is a groove (sulcus arteriae vertebralis), sometimes converted into a foramen by a delicate bony spiculum which arches backward from the posterior end of the superior articular process.
This groove represents the superior vertebral notch, and serves for the transmission of the vertebral artery, which, after ascending through the foramen in the transverse process, winds around the lateral mass in a direction backward and medially; it also transmits the suboccipital nerve (first spinal nerve). In a common anatomic variant the vertebral artery passes through an arcuate foramen.
On the under surface of the posterior arch, behind the articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlantoaxial ligament, which connects it with the axis.
Lateral masses
The lateral masses are the most bulky and solid parts of the atlas, in order to support the weight of the head.Each carries two articular facets, a superior and an inferior.
- The superior facets are of large size, oval, concave, and approach each other in front, but diverge behind: they are directed upward, medially, and a little backward, each forming a cup for the corresponding condyle of the occipital bone, and are admirably adapted to the nodding movements of the head. Not infrequently they are partially subdivided by indentations which encroach upon their margins.
- The inferior articular facets are circular in form, flattened or slightly convex and directed downward and medially, articulating with the axis, and permitting the rotatory movements of the head.
Vertebral foramen
Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament which stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts:- the anterior or smaller receiving the odontoid process of the axis
- the posterior transmitting the spinal cord (medulla spinalis) and its membranes
The transverse processes are large; they project laterally and downward from the lateral masses, and serve for the attachment of muscles which assist in rotating the head. They are long, and their anterior and posterior tubercles are fused into one mass; the foramen transversarium is directed from below, upward and backward.
Development
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The atlas ossifies from 3 centers.
Of these, one appears in each lateral mass about the seventh week of fetal life, and extends backward; at birth, these portions of bone are separated from one another behind by a narrow interval filled with cartilage.
Between the third and fourth years they unite either directly or through the medium of a separate center developed in the cartilage.
At birth, the anterior arch consists of cartilage; in this a separate center appears about the end of the first year after birth, and joins the lateral masses from the sixth to the eighth year.
The lines of union extend across the anterior portions of the superior articular facets.
Occasionally there is no separate center, the anterior arch being formed by the forward extension and ultimate junction of the two lateral masses; sometimes this arch is ossified from two centers, one on either side of the middle line.
External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.| Spine [ edit] |
| general structures: body of vertebra, vertebral arch (pedicle, lamina, vertebral notch), foramina (vertebral, intervertebral), processes (transverse, articular, spinous) cervical vertebrae: C1 (anterior arch, posterior arch, lateral mass), C2 (dens), C7, posterior tubercle, foramen transversarium thoracic vertebrae: costal facets (superior, inferior, transverse) lumbar vertebrae: accessory process, mammillary process sacrum/coccyx: pelvic surface (anterior sacral foramina, dorsal surface (posterior sacral foramina, median sacral crest, medial sacral crest, lateral sacral crest), lateral surface, base, sacral hiatus |
In vertebrates, cervical vertebrae (singular: vertebra) are those vertebrae immediately behind (caudal to) the skull.
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Variation among species
In some species, some parts of the skull may be composed of vertebra-like elements, e.g...... Click the link for more information.
Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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Anatomy (from the Greek ἀνατομία anatomia, from ἀνατέμνειν
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In vertebrates, cervical vertebrae (singular: vertebra) are those vertebrae immediately behind (caudal to) the skull.
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Variation among species
In some species, some parts of the skull may be composed of vertebra-like elements, e.g...... Click the link for more information.
vertebral column (backbone or spine) is a column of 34 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsal aspect of the torso, separated by spinal discs. It houses the spinal cord in its spinal canal.
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In Greek mythology, Atlas was one of the primordial Titans.
Atlas (Eng. /'æt ləs/ Gk. Ἄτλας) was the son of the Titan Iapetus (Eng. /aɪ'æ.pə.təs/) and the Oceanid Asia.
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Atlas (Eng. /'æt ləs/ Gk. Ἄτλας) was the son of the Titan Iapetus (Eng. /aɪ'æ.pə.təs/) and the Oceanid Asia.
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The word mythology (from the Greek μύθολογία mythología, from μυθολογείν mythologein
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head of an animal is the rostral part (from anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste).
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axis (from Latin axis, "axle") or epistropheus.
It forms the pivot upon which the first cervical vertebra (the atlas), which carries the head, rotates.
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It forms the pivot upon which the first cervical vertebra (the atlas), which carries the head, rotates.
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skull is a bony structure found in many animals which serves as the general framework for the head. The skull supports the structures of the face and protects the head against injury.
The skull can be subdivided into two parts: the cranium and the mandible.
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The skull can be subdivided into two parts: the cranium and the mandible.
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The Vertebral Column (singular: vertebra) are the individual irregular bones that make up the spinal column (aka ischis) — a flexuous and flexible column.
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The Longus colli muscle is a muscle of the human body.
The Longus colli is situated on the anterior surface of the vertebral column, between the atlas and the third thoracic vertebra.
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The Longus colli is situated on the anterior surface of the vertebral column, between the atlas and the third thoracic vertebra.
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MUSCLE (multiple sequence comparison by log-expectation) is public domain, multiple sequence alignment software for protein and nucleotide sequences.
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The anterior longitudinal ligament is a ligament that runs down the anterior surface of the spine. It traverses all of the vertebral bodies and intervertebral discs.
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The word concave means curving in or hollowed inward. The term is most commonly used to refer to:
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- Concave lens, a lens with inward-curving (concave) surfaces.
- Concave polygon, a polygon which is not convex.
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The dens or odontoid process or odontoid peg of the axis exhibits a slight constriction or neck, where it joins the body.
On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas.
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On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas.
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The anterior atlantoöccipital membrane (anterior atlantoöccipital ligament) is broad and composed of densely woven fibers, which pass between the anterior margin of the foramen magnum above, and the upper border of the anterior arch of the atlas below.
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The anterior atlantoaxial ligament is a strong membrane, fixed, above, to the lower border of the anterior arch of the atlas; below, to the front of the body of the axis.
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The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
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vestigiality is a term which describes homologous characters of organisms which have lost all or most of their original function in a species through evolution. These may take various forms such as anatomical structures, behaviors and biochemical pathways.
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The Rectus capitis posterior minor (Rectus capitis posticus minor) arises by a narrow pointed tendon from the tubercle on the posterior arch of the atlas, and, widening as it ascends, is inserted into the medial part of the inferior nuchal line of the occipital bone and the
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The Nuchal ligament is a fibrous membrane, which, in the neck, represents the supraspinal ligaments of the lower vertebræ.
It extends from the external occipital protuberance and median nuchal line to the spinous process of the seventh cervical vertebra.
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It extends from the external occipital protuberance and median nuchal line to the spinous process of the seventh cervical vertebra.
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The posterior atlantoöccipital membrane (posterior atlantoöccipital ligament), broad but thin, is connected above, to the posterior margin of the foramen magnum; below, to the upper border of the posterior arch of the atlas.
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The vertebral arteries are branches of the subclavian arteries.
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Cervical
They arise, one on each side of the body, then enter deep to the transverse process of the level of the 6th cervical vertebrae (C6)...... Click the link for more information.
The first spinal nerve, the suboccipital nerve exits the spinal cord between the skull and the first cervical vertebra, the atlas.
It supplies muscles around the suboccipital triangle including the rectus capitis posterior major, obliquus capitis superior, and obliquus
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It supplies muscles around the suboccipital triangle including the rectus capitis posterior major, obliquus capitis superior, and obliquus
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The vertebral arteries are branches of the subclavian arteries.
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Cervical
They arise, one on each side of the body, then enter deep to the transverse process of the level of the 6th cervical vertebrae (C6)...... Click the link for more information.
In human anatomy, arcuate foramen, also known as ponticulus posticus (Latin for "little posterior bridge"), refers to a bony bridge on the atlas (C1 vertebra) that covers the groove for the vertebral artery.
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The posterior atlantoaxial ligament is a broad, thin membrane attached, above, to the lower border of the posterior arch of the atlas; below, to the upper edges of the laminæ of the axis.
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Condyle L. fr. G. kondylos, knuckle, the knuckle of any joint, a round projection, rounded articular area (ex. condyles of the femur) one of the markings/features of bones, can refer to:
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- Lateral condyle
- Medial condyle
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The transverse ligament of the atlas is a thick, strong band, which arches across the ring of the atlas, and retains the odontoid process in contact with the anterior arch.
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