Atlas (anatomy)

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In anatomy, atlas (C1) is the most superior (first) cervical vertebra of the spine.

Named for the Greek mythology Atlas, as it supports the ball of the head.

The atlas is the topmost vertebra and with the axis forming a connection connecting the skull and spine. Atlas and special axes to allow for greater range of motion than normal vertebrae. They are responsible for nodding and turning the head.

The atlanto-occipital joint allows the head to nod up and down on the vertebral column. The dock acts as a pivot that allows the atlas and head attached to rotate on the axis, from side to side.

The peculiarity of the head atlas is that it has no body. It is like a ring and consists of anterior and posterior arches and two lateral masses.

Atlas and axes are important neurologically because the brain stem extends to the shaft.

Video Atlas (anatomy)

Structure

The anterior curve

The anterior arch constitutes about one-fifth of the ring: the anterior surface is convex, and presents at the center of the anterior tubercle for the adhesion of the longitudinal muscles and the anterior longitudinal ligament; the posterior is concave, and marked with a smooth, oval or circular facet ( fovea dentis ), for articulation with the odontoid process (nest) of the axis.

Upper and lower borders each attach to the anterior atlantooccipital membrane and anterior atlantoaxial ligaments; the first to connect it to the occipital bone above, and the last one with the axis below.

Posterior arch

The posterior arch makes about two fifths of the circumference of the ring: ends behind the posterior tubercle, which is a defect of the spinous processus and gives origin to Recepsi positises minores

The posterior portion of the arch presents above and behind the rounded edge for attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is the superior vertebral notch ( sulcus arteriae vertebralis ). This is a groove sometimes transformed into a foramen by a posterior atlantooccipital membrane ossification to create a smooth bone spikulum that curves backward from the posterior end of the superior articular process. This anatomical variant is known as the arcuate foramen.

This groove transmits the vertebral artery, which, after rising through the foramen in a transverse process, winds around the lateral mass backward and medial to enter the vertebrobasilar circulation through the foramen magnum; it also transmits the suboccipital nerve (the first spinal cord)

On the underside of the posterior arch, behind the inferior articular facet, there are two shallow grooves, the inferior vertebral notches. The lower bound provides an attachment to the posterior atlantoaxial ligament, which connects it with the axis.

Lateral mass

The lateral mass is the most dense and solid part of the atlas, to support the weight of the head.

Each carries two articular, superior and inferior aspects.

• The superior aspect is a large, oval, concave, and close to each other in the front, but diverges behind: they are directed upwards, medial, and slightly backward, respectively - forming a cup for the corresponding condyle of the occipital bone, and admirably adapted to the movement of the head nod. Not infrequently they are partly divided by indents that interfere with their limits.
• The inferior articular side is circular in shape, flat or slightly convex and directed downward and medial, articulate with axis, and allows the movement to turn the head.

vertebral foramen

Just below the medial margin of each superior side is a small tubercle, for the installation of transverse lacaments that extend across the atlas ring and divide the vertebral foramen into two unequal parts:

• anterior or smaller accept the odontoid process from the axis
• posterior that transmits the spinal cord ( medulla spinalis ) and its membrane

This part of the vertebral canal is large enough, much larger than that required for spinal marrow accommodation.

Transverse process

Large transversal process; they project laterally and downward from the lateral mass, and serve for the installation of muscles that help in turning the head. They are long, and their anterior and posterior tubercles converge into one mass; The transverse foramen is directed from bottom, up and back.

Development

The atlas is usually hardened from three centers.

Of these, one appears in each lateral mass around the seventh week of fetal life, and extends backward; at birth, these bone parts are separated from each other in the back by a narrow interval filled with cartilage.

Between the third and fourth years they unite either directly or through a separate central medium developed in cartilage.

At birth, the anterior arch consists of cartilage; in this separate center appearing around the end of the first year after birth, and join the lateral mass from the sixth to the eighth year.

The lines of unity extend across the anterior portion of the superior articular aspect.

Sometimes there is no separate center, the anterior arch is formed by the front extension and the final intersection of the two lateral masses; sometimes this curve hardens from two centers, one on either side of the center line.

Maps Atlas (anatomy)

Function

Musical Attachments

Transverse process

Top surface:

• anterior rectus capitis - the occipital bone (the inferior surface of the base)
• rectal lateral capitis - occipital bone (under jugular process)
• superior obliquus capitis - the occipital bone (between the superior and inferior nipple lines)

Interior and dorsal parts:

• obliquus capitis inferior - the process of rotating from the axis

Bottom surface:

• splenius cervicis (part) Ã, - spinous process T02-T05
• levator scapulae (part) Ã, - the superior part of the medial border of the scapula
• intertransversarius posterior cervicisÃ, - transverse process of the axis (posterior tubercle)
• anterior intertransversarius servicis - transverse process of the axis (anterior turbercle)

Posterior Tubercle

Top surface:

• the minor posterior rectus capitis - the occipital bone (the medial part of the interior nuchal line, and the intermediate surface and the foramen magnum)

Bottom surface:

• interspinalis cervicisÃ, - the rotating process of the axis

The anterior curve

• longus colli (superior oblique) Ã, - transversal process of C03-C05.

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Clinical interests

Rest in the first vertebra is referred to as a Jefferson fracture.

The junction of the craniocervical junction is also suspected as a factor in neurodegenerative diseases in which the altered CSF flow plays a role in the pathological process.

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Additional images

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See also

• Condilus Occipital

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References

This article combines text in the public domain of page 99 of the 20th edition of Gray's Anatomy (1918)

External links

• Netter, Frank. Atlas of Human Anatomy , "High Cervical Spine: C1-C2"

Source of the article : Wikipedia