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. Glymphatic circulation diminishes with age, which is believed to be responsible for the accumulation of waste products in the brain that causes Alzheimer’s disease and Parkinson's disease as well as the impairments of drainage that result in glaucoma, cerebral small vessel disease, multiple sclerosis, idiopathic normal pressure hydrocephalus, idiopathic intracranial hypertension, epilepsy, and headache disorders.
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, occurs as the interstitial spaces (between cells) in our brains increase 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 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. The inhalation portion of this glymphatic circulation process serves to drain the by-products of neural metabolism into venous and lymphatic circulation much like functional forces serve to drain the by-products of metabolism from other parts of the body. A recent study showed that yawning increases CSF and venous outflow.
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, long before anyone understood its cause. 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.
The human cranium is carefully designed to get through the birth canal. If it couldn't quite make it, that took two out of the gene pool. The movements of the cranial bones described in cranial osteology very much resemble the folding of the cranium necessary to make it long and narrow to get through the birth canal (extension of the cranial base during the outbreath), alternating with a rebound that makes the cranium shorter and wider (flexion of the cranial base during the inbreath). Thus, childbirth is the root of the cranial respiratory mechanism. The cranium goes into extreme extension to get through the birth canal, which makes it as long and narrow as possible and also squeezes the fluid from the lungs. Then, as soon as the head gets out, it rebounds into flexion, becoming shorter and wider in a contraction along with the rebound of the chest pulling in the first breath. Then a smaller cranial extension accompanies exhalation and the first cry. Then a still smaller cranial flexion with the next breath. This pattern of extension and flexion of the cranium slows down about 99.9% rapidly, and then it slows down about 99.999%, and eventually probably about 99.9999999%, but then it continues slowly throughout life. In this manner, It appears that the flexion of the cranium remains associated with inhalation, functioning to drain the waste products of neurologic activity, such as misfolded proteins like beta amyloid in Alzheimer's and alpha synuclein in Parkinson's, from the brain in the outflow portion of the glymphatic circulation process.
GLYMPHATIC DRAINAGE DURING CHEWING - cleans the frontal cortex. Power-crushing of food has an anterior component of force that moves a compressive wave anteriorly toward the cribiform plate, where 15-30% of glymphatic drainage occurs. In fact, chewing is such an important source of glymphatic drainage that cognitive decline in most of the world is correlated with the number of teeth lost, and depriving older animals of chewing by softening their food or removing their molars leads to loss of spatial memory, reduced learning cpacity, neuro-endocrinal changes, and hippocampal degeneration. In humans, studies show that chewing stimulates cranial circulation; which must be due to increasing glymphatic drainage, because the cranium is a closed shell with a relatively constant input pressure (arterial), so increased input is due to increased output.
IMPAIRED CRANIAL BONE MOVEMENT - occurring during this contraction and expansion of the cranium could impair glymphatic circulation. 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 less dramatic but still significant health problems 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.
HEADACHES - may also be due to impaired glymphatic circulation. One recent study described migraine and a "brain clearance disorder". Headaches are frequently associated with feelings of pressure. 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, and it's certainly plausible to postulate that localized areas of increased intracranial pressure due to the failure to adequately regulate glymphatic drainage in those regions could be the cause of the pain.
GLAUCOMA - may be due to impaired glymphatic circulation of the eyeballs, which apparently function much like little brains. 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.
NIGHTGUARDS - or other thick upper oral appliances could restrict movement between the two maxillary bones, so our oral appliances have 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 or dentistry 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 the interdigitation of the steeply cusped teeth can probably relapse those adjustments as soon as the patient bites and chews again. In an integrated biological system, a change anywhere requires at least a small change everywhere else, and a bite supported by unworn teeth 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 or to increase the strength of bite forces used in nocturnal bruxism by stabilizing the bite.
EXCESSIVELY LOCKED IN BITES - can cause tension in the walls of the cranium, 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.