Explain the movement of the Reciprocal Tension Membrane: sacral base moves posteriorly with cranial flexion. Which cranial motion is this associated with?

• A. Cranial extension
• B. Cranial flexion
• C. Neutral cranial position
• D. Transverse rotation

Answer: (B)

The reciprocal tension membrane describes a continuous tension of the dura mater from the cranial vault down to the sacrum. When the cranium flexes, the dural system tightens in a way that pulls the sacral base posteriorly. This linked movement—cranial flexion at the skull with a posteriorly directed sacral base—reflects how the dura transmits motion along the cranium–spine continuum. Conversely, cranial extension would tend to pull the sacral base anteriorly. So the movement described is associated with cranial flexion.