The brain and spinal cord – the two major components of the central nervous system (CNS) – require a carefully controlled physiological environment in order to develop and function efficiently and effectively.
The craniosacral system is largely responsible for providing this environment.
The craniosacral system is a physiological system that meets the criteria for classification as semi-closed and hydraulic. It has a watertight boundary largely provided by the external layer of the meninges. This external layer is known as the dura mater or dural membrane. The craniosacral system’s controlled fluid inflow is provided mainly by the choroid plexuses, with controlled outflow provided largely by the arachnoid granulation system. The fluid within the craniosacral system is cerebrospinal fluid (CSF), which is extracted from blood by the choroid plexuses and returned to blood by the arachnoid granulation system. The extraction and resorption of CSF are accomplished largely through osmotic pressures and specialized active transport mechanisms.
The functions of the CSF are carried out as it circulates within the craniosacral system. It circulates between the cells of the brain and spinal cord, and fills the spaces between cells. CSF also crosses cell membranes to enter intracellular compartments, though entry is selective. Some components of CSF are excluded. CSF functions include:
- Floating the brain so the effects of gravity are reduced by about 75-80 percent;
- Serving as a shock absorber so the brain is not traumatized by striking the inner surface of the cranium during sudden movements of the head or body;
- Providing nutrients to the brain and spinal cord, as well the pituitary and pineal glands, both of which are enclosed in the craniosacral system;
- “Washing away” metabolic waste products and toxic substances that have been deposited within and between cells of the CNS;
- Lubricating between cells of the CNS to prevent friction or improper contact that could short-circuit electrical nerve impulses or damage cell walls; and
- Maintaining the proper concentrations of electrolyte substances (ions) necessary for creating and transmitting nerve impulses so we can think, remember, feel and move.
The dural membranes of the craniosacral system form the lining for several cranial (skull) bones. These membranes also attach to specific areas of bone in the spinal canal. The spinal canal attachments are much more sparse than the intracranial attachments, which allows for movement of the spine. When dural membrane movements are abnormally restricted for any reason, the craniosacral system may become compromised, with secondary effects on the CNS and/or endocrine and immune systems.
The volume of CSF in the craniosacral system constantly and rhythmically rises and falls at about six to 12 cycles per minute. This ongoing volumetric change requires dural membrane boundaries to continually adapt to avoid excessive fluid pressures on the delicate brain and spinal cord structures. Part of this accommodation is accomplished by the cranial bones opening and closing minutely where they abut each other.
It is now known that under normal circumstances cranial bones do not fuse together at puberty, as was previously taught.1-6 Rather, they are in constant motion to accommodate the changing demands placed on them by the dural membrane as it adjusts to the rhythmical rise and fall of CSF volume.
Disease, dysfunction or injuries may cause loss of bone mobility in the head, spine or pelvis. Such trauma can cause craniosacral system dysfunction, with secondary ramifications in the CNS, endocrine and immune systems.