Cranial and Craniosacral
SUMMARY - The human cranium is composed of bony plates connected by wavy sutures that give it the flexibility required to squeeze through the birth canal. Later, they fill in with bone until almost all of them have "ossified" by adulthood, but that ossification of the sutures does not completely immobilize them. Afterwards, they participate in an almost imperceptible pumping system in which the cranium expands and contracts in synchrony with breathing in a process that circulates cerebrospinal fluid (CSF). This process is called glymphatic circulation, like lymphatic circulation for the glial cells of the brain. Cranial osteopaths described the movements of each cranial bone in this cranial respiration process half a century before anyone understood its cause. Glymphatic circulation diminishes with age, which may be responsible for the accumulation of waste products in the brain, which appear to cause Alzheimer’s disease, Parkinson's disease, and other neurodegenerative diseases. Disruption of the glymphatic circulation process may also cause the fluctuations in localized CSF pressures that are probably responsible for migraines.
BACKGROUND - The cranium was considered a rigid shell with a genetically determined shape until high precision ultrasound in the late 20th century showed that it is actually a dynamic system that changes shape in response to gravity, coughing and sneezing. Inside the cranium, the brain is bathed in cerebrospinal fluid (CSF). The brain is the most metabolically active organ in the body, producing more than 1300 grams of macromolecular metabolites. These waste products need regular drainage. In other parts of the body, waste products are flushed out by the venous and lymphatic drainage that gets stimulated by functional movements; because veins have one-way valves, and exercise operates them like a pump to help drain the capillary beds. However, the cranium is too rigid to employ movement to assist in the drainage of waste products. Therefore we employ a different mechanism to clean our brains (brainwashing) during sleep.
GLYMPHATIC DRAINAGE - During sleep, especially slow wave sleep, the interstitial spaces (between cells) in our brains increase 60% to become a mixing chamber, and the perivascular spaces house a CSF circulation process that alternates negative intrathoracic pressure from the lungs to suck out waste products and positive arterial pressure from the heart to replenish the tissues while rhythmically moving the cranial bones back and forth in very small amounts to accommodate the pumping. During each inbreath, the negative intrathoracic pressure from inhalation sucks out 1-2 drops of interstitial fluid and neurologic waste products from the cranium into venous circulation by shortening the cranium antero-posteriorly along with flexion of the spheno-occipital synchondrosis and external rotation of the temporal bones in a smooth steady process that moves large volumes of CSF slowly, while peri-arterial flow slows. Then, during each exhalation, arterial pulsation replaces those fluids with fresh CSF in a stepwise process that moves small volumes of CSF rapidly, while peri-venous flow slows, and the cranium rebounds along with extension of the spheno-occipital synchondrosis and internal rotation of the temporal bones.5-10 The inhalation portion of this glymphatic circulation process serves to drain the by-products of neural metabolism into venous circulation much like functional forces serve to drain the by-products of metabolism from other parts of the body into venous circulation.
CRANIAL OSTEOPATHY - The complex movements of the individual cranial bones during this expansion and contraction process were elegantly described long ago by cranial osteopaths. Sutherland believed that cranial respiration was a primary process, - beginning in the brain and then moving through all the other tissues. Magoun understood that inhalation was associated with cranial flexion, but he still believed that cranial respiration had a timing different from lung respiration. Upledger believed that the cranial respiratory rhythym was caused by a stretch reflex in the cranial sutures, which responded to each incident of cranial expansion due to production of CSF by reducing CSF production to maintain intracranial pressure equilibrium. Numerous cranial osteopaths described how to feel for the particular movement of each cranial bone in this cranial respirtation process and how to apply gentle manual manipulations to restore cranial movements that were restricted. Even if they misunderstood the source of the movements, their work to identify blockages to it and techniques for restoring it with light manual pressure may turn out to be extremely valuable, now that we realize that the cranial respiration process they described so elegantly turns into a brain waste clearance mechanism during slow wave sleep.
It's certainly reasonable to hypothesize that movement restrictions at the cranial sutures could impair this glymphatic circulation process. We know that completely immobilizing a cranial suture is detrimental. In a condition called craniosynostosis, an early head injury or birth trauma causes a cranial suture to fuse, which impairs growth in all the surrounding cranial bones, alters head shape, and causes a number of symptoms. A partial or limited craniosynostosis could cause a less dramatic but still significant health impairment by impairing the CSF circulation process in portions of the cranium. The brain consistently turns out to be more sensitive than we can measure, and it could be affected in many ways that we do not yet understand by even minute changes in the pressure of its housing.
It's also likely that headaches are due to impaired glymphatic circulation. A study in mice recently showed that the cortical spreading depression, which is a hallmark of migraines, is accompanied by several minutes of closure of the perivascular spaces, which would result in impaired clearance of waste along the perivenous pathways and increased local CSF pressure. Headaches are frequently associated with feelings of pressure, and there's no reason to believe that those intracranial pressure sensors are not as accurate as they are in every other part of our bodies.
Many cranial osteopaths believe that a common source restricted movement between the two maxillary bones is the rigidity of thick upper nightguards, so we make all our oral appliances with minimal acrylic crossing the midline, as shown below left. We also offer appliances that have no rigid materials crossing the midline but instead have the two sides connected only by loops of flexible braided stainless steel wire, as shown below right.
THE ROLE OF THE BITE IN POSITIONING THE FACIAL BONES - A fact that has not yet been incorporated into cranial osteopathic work is that the positions of the facial bones are largely controlled by bite forces. In a study illustrated below, bite forces applied to a cranium coated with stress sensitive paint showed that they are distributed throughout the front of the cranium.
Bite forces are much stronger than the light manual forces used to make cranial osteopathic adjustments, so they can probably relapse one of those adjustments as soon as the interdigitation of the steeply cusped teeth returns the facial bones to the exact positions (within microns) that they had before the adjustment.
Also the direction, location, and strength of the bite forces vary greatly depending on the contours of the bite table. People who wear dentures or are undergoing orthodontics with braces have low bite forces. People under stress have higher and more frequent bite forces. Some people have bites that are directed unilaterally (they chew on one side), some have bite forces that extend out widely bilaterally, and others have bite forces that are directed almost entirely vertically.
Oral appliances could be used to control the application of bite forces to the cranium. For example, a front flat bite plate oral appliance moves the location of the bite forces about an inch anteriorly. An oral appliance can easily shift bite forces to either side.
The contours of the bite table also affect the way the face grows, because the bite functions like a cranial suture connecting the upper and lower jawbones, and cranial sutures provide adaptability to accommodate irregularities in growth of individual bones. Such adaptability is needed in the bite, because the upper and lower jawbones grow by very different mechanisms, at slightly different rates, and in slightly different directions. However, in many modern human bites, the unworn teeth are so steeply interdigitated that they leave the bite without sufficient adaptive capacity to accommodate the natural discrepancies between the normal growth patterns in the upper and lower jawbones.The elongation of the mandible cannot push its corpus (the area containing the lower teeth) further forward, because that area of the mandible is locked to an upper jaw that grows by expanding rather than translating; and the upper jaw cannot expand, because it is locked to a mandible which grows by translating rather than expanding. The result of this locking together of the upper and lower jawbones by the bite is best described as a partial craniosynostosis of the maxillo-mandibular suture. Like in other craniosynostoses, the resulting strains are likely to be transmitted throughout the cranium.
CRANIOSACRAL TREATMENT - is an extension of cranial work to include the spinal canal, which is enclosed in the same CSF reservoir as the cranium; but where CSF flow is slower, more turbulent, and probably less consequential. The early osteopaths described how the tail end of the spine moves up during flexion (inhalation) and down during extension (exhalation). The hydrodynamics of CSF in the spinal canal are better known than those in the cranium, because they are more easily imaged and monitored. Blockages to the normal CSF flow through the spinal canal due to Chiari malformation, spina bifida, a cyst, spinal cord tethering, space occupying lesions, trauma, or infection impair the flow immediately above and below the blockage; but distal to the blockage, CSF flow resumes with epidural and cord pulsation. In minor blockages, the flow reflects local turbulence and eddies. In major blockages, the flow may be stopped completely. Removing the blockage surgically restores the flow and eliminates the symptoms.
Much of the clinical success from craniosacral treatment may be produced by other benefits of manual manipulation of the spinal column. The cranium functions as the superior end of the spine, therefore holding the occiput in one hand and the sacrum in the other when a patient lies on a table enables a therapist to feel the mobility of the whole spinal column and manipulate it in various ways that can enhance its range of motion, improve intervertebral joint circulation, or provide other benefits that we don't yet understand.