What is the Primary Respiratory Mechanism (PRM), foundation of Cranial Osteopathy ?

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The cranial rhythmic impulse (CRI) refers to the palpatory sensation of the widening and narrowing of the skull.

• Normal rate: 8–14 times per minute

• A result of the PRM

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​The PRM is composed of five elements :

1. Inherent motility of the brain and spinal cord

   • Brain and spinal cord have an inherent wave-like motion.

   • Described as coiling and uncoiling of the central nervous system (CNS).

2. Fluctuations of the cerebrospinal fluid (CSF): volume of CSF changes in relation to the cranial rhythmic impulse (CRI).

3. Mobility of the intracranial and intraspinal membranes

   • The meninges surround the CNS and are made up of the dura, arachnoid, and pia mater.

   • A continuous connection is present from the foramen magnum to the cervical vertebrae and second sacral segment.

   • These membranes move due to the inherent motility of the brain and spinal cord and fluctuations of the CSF.

   • Motion of these membranes causes the cranial bones and sacrum

      to move in relation to one another.

4. Articular mobility of cranial bones

   • Although cranial sutures fuse shortly after birth, they contain small motions that cannot be felt individually.

   • An amalgamation of the cranial bones and multiple sutures allow for palpable motion.

5. Involuntary mobility of the sacrum between the ilia

   • The dural connection between the cranium and S2 of the vertebral column causes sacral movement.

   • This dural connection is termed the reciprocal tension membrane (RTM).

   • The bones move in rhythm with the motion of the shifting tensions of the RTM.

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The primary physiologic motion is between the articulation of the sphenoid and the occiput called the sphenobasilar synchondrosis (SBS).​ It moves in a biphasic cycle (flexion and extension) in response to the pull of the reciprocal tension membrane and fluctuations of the CSF.​