Type & Articular surface
These are synovial joints of the ellipsoid variety.
Above: The occipital condyles, which are convex
Below: The superior articular facets of the atlas vertebra.
These are concave.
The articular surfaces are elongated,
and are directed forwards and medially.
Ligaments
I. The fibrous capsule surrounds the
joint.
It is thick posterolaterally and thin anteromedially.
2. The anterior atlanto-occipital membrane extends from the anterior margin of the foramen magnum above, below to the upper border of the anterior arch of the atlas. Laterally, it is continuous with the anterior part of the capsular ligament,
anteriorly it is strengthened by the cord-like anterior longitudinal ligament.
3. The posterior atlanto-occipital membrane extends from the posterior margin of the foramen magnum above, to the upper border of the posterior arch of the atlas below.
Inferolaterally, it has a free margin which arches over the vertebral artery and the first cervical nerve.
Laterally, it is continuous with the posterior part of the capsular ligament.
Blood Supply & Nerve Supply
The joint is supplied by the vertebral artery and by the first cervical nerve.
Movements
they permit movements around two axes.
Flexion and extension (nodding) occur around a transverse axis.
Slight lateral flexion is permitted around an anteroposterior axis
I. Flexion is brought about by the longus capitis and the rectus capitis anterior.
2. Extension is done by the rectus capitis posterior major
and minor, the obliquus capitis superior, the semispinalis capitis, the splenius capitis, and the upper part of the trapezius. 3. Lateral bending is produced by the rectus capitis, the
semispinalis capitis, the splenius capitis, the sternocleidomastoid, and the trapezius
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