What motion unit is affected by atlas superior?

What motion unit is affected by atlas superior?

• A. Occiput-C1
• B. C1-C2
• C. T1-T2
• D. L4-L5

Answer: (A)

The key idea is that atlas superior describes the joint where the atlas (the first cervical vertebra, C1) meets the skull. The superior articular facets of C1 pair with the occipital condyles of the skull to form the atlanto-occipital joint. This motion unit is the articulation between the occiput and C1, so it governs head nodding—flexion and extension—with a little lateral bending. Rotational movement of the head is mainly handled by the atlanto-axial joint between C1 and C2, not by atlas superior. So the motion unit affected by atlas superior is the Occiput-C1 joint. The other options involve different parts of the spine: C1-C2 is the atlanto-axial joint for rotation, while T1-T2 and L4-L5 are in the thoracic and lumbar regions, not involved with atlas superior.

The key idea is that atlas superior describes the joint where the atlas (the first cervical vertebra, C1) meets the skull. The superior articular facets of C1 pair with the occipital condyles of the skull to form the atlanto-occipital joint. This motion unit is the articulation between the occiput and C1, so it governs head nodding—flexion and extension—with a little lateral bending. Rotational movement of the head is mainly handled by the atlanto-axial joint between C1 and C2, not by atlas superior. So the motion unit affected by atlas superior is the Occiput-C1 joint. The other options involve different parts of the spine: C1-C2 is the atlanto-axial joint for rotation, while T1-T2 and L4-L5 are in the thoracic and lumbar regions, not involved with atlas superior.