When Sutherland defined the two stages of the craniosacral rhythm, he called them flexion and extension because he considered the SBS to be the center of movement. In conforming to the nomenclature, flexion of the SBS corresponds to a reduction in the angle between the basilar part of the occiput and of the sphenoid body. Extension corresponds to an increase in this angle.
The occipital bone makes a backward rotation, and the sphenoidal bone makes a forward rotation, in which the SBS rises. Globally, both bones make a forward movement. This is important for the relationship between occiput and atlas. In cranial flexion, the occipital bone slides forward over the atlas (Fig. 4.6a). This corresponds to a mechanical extension of the occiput. The ethmoidal bone, lying in front of the sphenoidal bone, makes the same rotation as the occipital bone. The paired or peripheral bones make an external rotation during flexion.
The forward movement of the occipital bone and upward movement of the basilar part shift the foramen magnum forward. This results in a cranial pull on the spinal dura mater. Consequently, the base of the sa
Fig. 4.6a, b a Biomechanics of cranial flexion: movement of the occiput over the atlas, b Biomechanics of cranial extension: movement of the occiput over the atlas.
crum is pulled upward, causing an extension in the sacrum and stretch in the spinal column.
Extension of the craniosacral mechanism (Fig. 4.6b) causes a movement in the opposite direction. The SBS drops, the occiput rotates forward, and the sphenoidal bone rotates backward. The basilar part and the foramen magnum move backward. From a mechanical standpoint, this corresponds to a flexion of the occiput.
The dural tube drops and the sacrum moves forward into the nutation. The ethmoid rotates forward, like the occiput. The peripheral bones make an internal rotation.
In addition to the physiological movements flexion-extension, which are induced by the organism's inherent powers, the primary respiratory mechanism (PRM), Sutherland described other movements (torsion, sidebending rotation, vertical strain, and lateral strain), which are explained in the following.
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