The cranio-sacral system is made up of the spinal chord and brain, the connective tissue around the spinal chord and brain, and the bones of the skull and the spine. In the 1920s Wiliam Sutherland, Doctor of Osteopathy, did experiments on his own cranium to discover, as he expected, the cranial sutures allow for a subtle involuntary movement between the bones. From his experiments, Cranial Osteopathy was born. Cranial Osteopathy was considered an esoteric embarrassment by much of the Osteopathy institution (Upledger, 2009).
It wasn’t until decades later that Sutherland’s hypothesis gained greater acceptance when John Upledger researched the scientific mechanics of the system at Michigan State University in the 1970s. Upledger showed that, indeed, the sutures operate like hinges on a bridge that make the structure stable in the midst of movement and temperature fluctuations. The sutures allow these bones to make room for the rhythmic constant shifting of pressure in the membranes surrounding the central nervous system (CNS). When adhesions inhibit the movement of these bones, it can create any number of local or distal symptoms.
Cranio-Sacral Therapy is used to diagnose and treat dysfunctions within this system. It is a deeply cooperative approach between the therapist and the client’s own intelligent body.
Dural Tube This tube of connective tissue wraps and protects the spinal cord and is the container for the meninges and cerebro spinal fluid (CSF). When the dural tube is free from adhesions it glides freely within the spinal canal. Its bony attachments are at C2 and C3, S2, and the foramen magnum at the base of the skull.
There are 22 bones in the adult human cranium. They are listed below with a rough laymen’s terms description of location.
Frontal bone: forehead
Parietals: around the ears
Temporals: sides of the head
Occiput: at the back of the head above the neck.
Sphenoid: in the centre of the head above the spinal column and behind the eyes. It touches the surface at one point in the temples. It is shaped like a butterfly or double vertebrae. It houses the pituitary.
Ethmoid: between the eyes at the root of the nose.
Jaw and Face
Mandible: the jaw
Maxillae: the upper jaw and teeth
Vomer: attaches to the septum of the nose, the ethmoid and the sphenoid. Deep to the septum.
Palatines: make up the back roof of the mouth.
Zygoma: the cheek bones.
Nasal bones: stem off of the ethmoid to form the bridge of the nose
Nasal Concha: curled bones inside the nasal cavity.
In a sense, it’s amazing, with so many separate bones with multiple joints on each, that it took so long to realize the bones may have individual movement capacity. Each pairing of bones has its own pattern of flexion and extension in relation to each other. I find that I primarily work with the 8 cranial bones and, with the exception of the mandible, rarely get into the other facial bones.
When one bone is impeded in its movement it affects others. When the bones of the skull are operating without restriction, they can be used almost like handles to effect restrictions to the dural tube along its length or the fascial membranes within the brain. The Upledger model is quicker to jump to this these direct mobilization techniques. Other techniques, such as Biodynamic Cranio-Sacral Therapy as taught by Franklyn Sills, are characterized by an emphasis on listening and affecting with intention before going to directional coercion.
Intracranial Membrane (Reciprocal Tension Membrane)
In short, there’s a horizontal membrane and a vertical membrane that come together at the back of the head and attach to the dural tube and spine. There are three layers to these membranes. The dura mater is the outer layer, the arachnoid is the middle layer and the pia mater is the inner layer. Between the arachnoid and the pia mater is a space where the CSF flows.
The vertical membrane, separating the left and right hemisphere, is the falx cerebri and attaches to the ethmoid, and frontal bone and along the suture between the parietals to the back of the occiput where it meets the tentorium. The tentorium go from one temporal bone to the other cradling the posterior cerebrum and dividing it from the cerebellum. It attaches in the back to the occiput and in front to the sphenoid.
There’s only about four ounces of this fluid in the body, which diminishes with age. Its job is to flush toxins from the brain and nurture the brain and spinal chord. One might imagine that, with such limited resources, the impeding of the flow of such liquid due to adhesions can have strong repercussions.
The CSF cycles around the brain and spinal chord 6-12 times per minute. One cycle includes a flexion stage and an extension stage. The flexion stage is characterized by subtle, palpable filling, widening and external rotation. Then there is a tiny pause before the extension phase of emptying, elongating, and internally rotating. The movement of this fluid is often called a tide and is compared to the tides of the ocean. Some can even feel what they call a short tide, described above and a much longer tide. You might think of this as waves in the ocean and the tidal fluctuations. Both are happening all the time, but the longer tide is harder to notice.
Movement of the Bones
In flexion the sphenoid and occiput tip away from each other with the sphenoid tipping forward and the occiput back. The frontal bone tips forward and the temporal bones rotate out and widen while the parietal bones lift. The opposite motion occurs in extension.