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, these sutures 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, headaches, glaucoma, and several lesser known 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).
GLYMPHATIC DRAINAGE – During sleep, especially slow wave sleep, the interstitial spaces (between cells) in our brains increase as much as 60% to become a mixing chamber, and the perivascular spaces (surrounding the vessels like sleeves) open up to house a CSF circulation process that employs both positive arterial pressure and negative intrathoracic pressure to pump fluids through the cranium along side blood vessels and nerve pathways while rhythmically moving the cranial bones back and forth in very small amounts to accommodate the pumping. Each inbreath 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 relatively large volumes of CSF slowly, while peri-arterial flow slows. Then, during each exhalation, the cranium rebounds, along with extension of the spheno-occipital synchondrosis and internal rotation of the temporal bones, due to arterial pulsation in a stepwise process that moves smaller volumes of CSF more rapidly, while peri-venous flow slows. 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.
Glymphatic drainage in the frontal cortex also occurs during chewing, which produces a wave of compressive force anteriorly toward the cribiform plate, where 15-30% of glymphatic drainage occurs. Chewing is such an important source of glymphatic drainage that cognitive decline is correlated with tooth loss, and animals deprived of chewing behavior by softening their food or removing their molars undergo rapid cognitive decline.
CRANIAL OSTEOPATHY - The complex movements of the individual cranial bones during this expansion and contraction process were elegantly described long ago by cranial osteopaths, who described it as a tidal flow that you could only feel by being very still. 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. Numerous cranial osteopaths described low force manual manipulations that could be used to restore restricted cranial movements.
It's certainly reasonable to hypothesize that restricted cranial movements could impair this glymphatic circulation process. Completely immobilizing a cranial suture in craniosynostosis 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 many headaches are due to impaired glymphatic circulation. A study in mice recently showed that the cortical spreading depression, which is the hallmark of migraines, facilitates 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. One recent study described migraine and a "brain clearance disorder". Headaches are frequently associated with feelings of pressure, and there's no reason to believe that those intracranial pressure sensors producing sensations of pressure are not as accurate as they are in every other part of our bodies. Localized areas of increased intracranial pressure due to the failure to adequately regulate glymphatic drainage in those regions could certainly be the cause. We don't yet have intracranial pressure sensors sensitive enough to detect small deviations of pressure, to which the brain could be much more sensitive than we can currently measure.
There's also good evidence that glaucoma may be due to impaired glymphatic circulation. Glaucoma is the result of excessive ocular pressure, and researchers recently identified an “anterograde ocular glymphatic clearance system” in rodents that removes Aβ and other metabolites from the intraocular space via retinal ganglion cell axons and perivenous spaces of the retina and optic nerve head.
Thick upper oral appliances or nightguards could restrict movement between the two maxillary bones, so oral appliances should be made with minimal acrylic crossing the midline, as shown below left. We can also make 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.
The role of bite forces in glymphatic drainage is the reason for the linkage between jaw muscle function and cognitive decline. Depriving older animals of chewing by softening their food or removing their molars leads to loss of spatial memory, reduced learning capacity, neuro-endocrinal changes, and hippocampal degeneration. In humans, loss of teeth is associated with faster cognitive decline, and chewing stimulates cranial circulation and frontal cortex activity. Jaw muscle firing compresses the cranium vertically, which helps pump out neurologic waste products such as misfolded proteins through perivenous channels.
Bite forces are much stronger than the light manual forces used to make cranial osteopathic adjustments, so they can probably relapse 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. In an integrated biological system, a change anywhere requires at least a small change everywhere else, and a steeply interdigitated bite prevents even a minute change in the braced position and thereby also the posture of the mandible.
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 extreme stress often have sustained increases in jaw muscle tonus. 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. People with steep unworn dentitions and tall interlocking cusps on their teeth are more likely to encounter transversely directed forces from chewing.
Oral appliances can alter the strength and location of bite forces applied to the cranium. For example, a front flat bite plate oral appliance moves the location of the bite forces about an inch anteriorly. A tall oral appliance can cause sustained light bite forces from passive stretch of the jaw closing muscles. An oral appliance can be used to shift bite forces to either side. A stable oral appliance can increase the strength of bite forces used in nocturnal bruxism when the natural bite is unstable.
The tension in the walls of the cranium is probably affected by the bite, 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.