[PT Y1 A2] Atlas, Axis, and Craniovertebral Jts

II. Craniovertebral joints A. Atlanto-occipital joints 1) The ____ of each side lies between the concave superior articular facet on the lateral mass of the atlas and the corresponding convex occipital condyle. Each joint is enclosed by an articular capsule that is thin and loose. 2) These two bones are also connected by ____ that extend from the anterior and posterior arches of the atlas to the anterior and posterior margins of the foramen magnum respectively. 3) Functionally, the two joints act together as a biaxial ellipsoid joint. The movements permitted are flexion and extension, as in nodding the head "___", around a transverse axis; and slight side bending to one or the other side around an anteroposterior axis.

atlanto-occipital joint anterior and posterior atlanto-occipital membranes yes

B. Axis or second cervical vertebra 1) The axis is characterized by the ___ or odontoid process that projects upward from the body of the axis. The dens articulates in front with the anterior arch of the atlas and behind with the transverse ligament of the atlas to form the median atlanto-axial joint. 2) The large oval superior articular facets are convex anteroposteriorly and flat or concave transversely. They articulate with the inferior facets of the atlas at the lateral atlantoaxial joints. 3) The spine is large and ___, the transverse processes short and blunt, and the pedicles and laminae thick.

dens bifid

B. Atlanto-axial joints 1) There are three synovial joints between the atlas and axis: two lateral plane joints and a median pivot joint. 2) The paired____ are plane joints between the opposed articular facets of the atlas and axis. The articular capsules are thin and loose. Each capsule is strengthened posteromedially by an accessory atlanto-axial ligament that extends from the body of the axis upward to the lateral mass of the atlas. 3) The ____ is a uniaxial pivot joint between the dens of the axis and the ring formed by the anterior arch of the atlas and its transverse ligament. It consists of two separate articulations and synovial cavities: one between the front of the dens and anterior arch; the other between the back of the dens and transverse ligament. 4) The ____ is a thick strong band that extends between the tubercles on the medial surfaces of the lateral masses of the atlas. It passes behind the dens and holds it in contact with the anterior arch. From the middle of the ligament a small ____ passes upward to the anterior edge of the foramen magnum, and an ____ passes downward to the back of the body of the axis. Hence the whole ligament forms a cross and is named the ____ 5) Movement at the three atlanto-axial joints consists primarily of rotation of the skull and atlas on the axis, as in shaking the head "no". The dens of the axis serves as a pivot around which the atlas and skull turn. The extent of rotation is limited by the alar ligaments. The atlanto-axial joints also contribute to flexion and extension of the neck.

lateral atlanto-axial joints median atlanto-axial joint transverse ligament of the atlas superior band inferior band cruciform ligament of the atlas.

I. Atlas and axis A. Atlas or first cervical vertebra 1) The atlas is a ring-shaped vertebra that lacks a body and a spine. It consists of two elliptical ____ connected by a short ____ and a longer curved posterior arch. The position of the body is occupied by the dens of the axis to form a pivot around which the atlas and skull turn. The spine is represented by a small ____ on the ____. There is also a midline anterior tubercle on the anterior arch. 2) Each lateral mass has superior and inferior articular facets. a) The____ are elongated and concave and face medially. The superior facets articulate with the convex occipital condyles to form the paired atlantooccipital joints. b) The ____ are almost circular, flat or slightly concave, and face medially and slightly backwards. They articulate with the superior facets of the axis to form the paired lateral atlanto-axial joints. 3) The posterior arch is grooved on its upper surface behind each lateral mass by the vertebral artery and veins. 4) The long transverse processes project laterally and anteriorly and are palpable between the mastoid process and angle of the mandible. Each has a foramen for the vertebral artery.

lateral masses anterior arch posterior tubercle posterior arch superior facets inferior facets

C. Ligaments connecting the axis with the occipital bone 1) The ____ (tectorial membrane) is a broad, thick band that covers the dens and its ligaments within the vertebral canal, and is the upward extension of the posterior longitudinal ligament. From the body of the axis it expands as it passes upward and is attached to the basilar part of the occipital bone in front of the foramen magnum. 2) The paired ____ are strong rounded cords that arise on either side of the apex of the dens and pass upward and laterally to the medial side of each occipital condyle. These ligaments limit the extent of rotation at the atlanto-axial joints. 3) The apical ligament of the dens is a slender band that extends from the apex of the dens to the anterior margin of the foramen magnum.

membrana tectoria alar ligaments