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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