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Simplified Craniosacral System Overview

Many of my clients have asked me for a simple explanation of the Craniosacral System. Here is a basic overview of how it is seen in the bio-mechanical model:

The word “craniosacral.
comes from the membrane system
that surrounds the central nervous system
and connects the cranium to the sacrum

It consists of:

  • The cranium
  • The sacrum and coccyx
  • The meninges
  • Cerebrospinal fluid
  • The structures involved in the production and re-uptake of CSF

The Cranium

The cranium consists of 22 bones and about 115 or 120 joints, depending on how they formed. This bony structure makes a hard-shell that protects the brain and allows for some flexibility. In fact, the bones are thinner and more flexible than most people realize. Bones around the temple and in the sinuses are thin enough to be translucent. Think of these bones as being more flexible, like your ribs. Cranial bones are held together by sutures and an internal membrane system.

The bones around the brain form the “vault.” Reciprocal tension membranes form partitions dividing the vault into upper, lower, left, and right sections. The reciprocal tension membranes support the brain and provide a balance of tension for the structure. The falx cerebri and falx cerebelli divide cranium into left and right halves. The tentorium cerebelli forms a tent over the cerebellum, separating it from the cerebrum. 

It is interesting to note that these membranes are heavily populated with proprioceptors, which feedback information about tension and position.

The meninges are a triple-layered membrane system that surrounds, supports, and protects the central nervous system. The dura mater (“tough mother”) forms the outside layer against the bone. The arachnoid (“spider”) is a spongy, cob-web like membrane that adheres to the dura mater. The pia mater (“soft mother”) is a thin layer that lines the surface of the central nervous system. There is room for fluid to flow in the “sub-arachnoid space.” That’s the space between the arachnoid and the pia mater. The membranes provide protective padding and containment of the cerebrospinal fluid in which the central nervous system floats.

The membranes form a dense ring around the big hole where the spine exits the cranium (foramen magnum). Then, they form a tube that surrounds the spinal cord. That tube attaches firmly to the hole in the cranium and skips the first vertebrae. Next, the membrane attaches to the second and third vertebrae in the neck, skips the rest of the spine and attaches to the second segment of the sacrum. Eventually, this tube narrows to become a filament that attaches to the coccyx.

Add block

The reciprocal tension membranes join to each other and to the wall of the cranium. At those connections, they create little channels for blood flow called venous sinuses. These venous sinuses are shown in blue on the right of the cranial base in this illustration. The channels form free-flowing exits for blood and cerebrospinal fluid. They are key to the regulation of intracranial pressure.

The pituitary gland sits in a saddle in the center of this structure. It feeds the hormones to the venous sinuses, which carry them to the jugular vein and out to the body. 

Ventricles are balloon-like structures at the center of the brain. They support the neural tissue of the brain so that it floats above the floor of the cranium. They also create Cerebrospinal fluid (CSF). Hair-like vessels, called the Choroid Plexus, filter CSF from the blood. CSF flows out of the ventricles into subarachnoid space. Once there, CSF offers structural support, protection, nutrition, and waste removal.

CSF returns to the blood via small valves in the venous sinuses.  The central nervous system, which is a firm gelatinous structure, floats in the cerebrospinal fluid. This cushions and protects the sections of the CNS like stewed tomatoes in a jar of water.

The detail of its architecture and function is truly amazing. This system provides nourishment, protection, pressure regulation, sensory feedback, and more.

Volumes have been written about this system and it’s structures. I will be adding more about this to my blog on a regular basis.

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