During SBS extension, what is the relationship between the sphenoid and occiput?

• A. They approximate and move superiorly
• B. They separate and move inferiorly
• C. They rotate around the occipital condyles
• D. They remain stationary

Answer: (A)

In the cranial primary respiratory mechanism, the sphenoid and occiput act as a paired unit around the sphenobasilar synchondrosis. When the SBS is extended, the two bones move toward one another (approximate) and the motion is toward the vertex as a unit. This means the sphenoid and occiput come closer together and their articulating surfaces effectively move in a superior direction as part of the extension pattern.

The alternative ideas describe either separation of the bones and a downward (inferior) shift, rotation around the occipital condyles, or no movement at all, none of which align with the extension pattern in this framework.