Cephalorachidian Fluid: Pillar Of The Central Nervous System
The cerebrospinal fluid (CSF) or cerebrospinal fluid is one of the main fluids in the human body. Its main function is to protect the cerebral cortex and the spinal cord. It therefore acts as a shock absorber in the event of a collision between the central nervous system and the skull, or surrounding bones. Under normal conditions, the LCR measures a volume between 100 and 150 mL.
The cerebrospinal fluid is transparent, its chemical content is different from that of serum, but similar to that of blood plasma. It has the same consistency as water and is essentially composed of H2O, minerals (sodium, potassium, calcium, chlorine), inorganic salts (phosphates) and vitamins (especially of group B). It also contains electrolytes, leukocytes, amino acids, choline and nucleic acid.
Cephalorachidian fluid : an extracellular fluid
The body has 4 liquid compartments which are divided into intracellular and extracellular. About two thirds of the total water in our body is composed of intracellular or intravascular fluid. In other words, the liquid part of the cytoplasm of cells. The rest is extracellular. There are 3 fluids of the latter type.
- Blood plasma, which is the liquid part of the blood that is contained in the blood vessels and heart cavities.
- The interstitial fluid, also called tissue, found in the interstitium or space between cells.
- The cerebrospinal or cerebrospinal fluid, which bathes the brain and spinal cord. Below we will deepen their composition, location and functions.
Location and circulation
The cerebrospinal fluid circulates in the subarachnoid space, in the cerebral ventricles and in the ependymal canal. Let’s go by parts:
- The subarachnoid space is located between the intermediate (arachnoid) and the innermost (pia mater) menynx. The pia mater is in contact with the brain surface, which is why this small space in which the cerebrospinal fluid circulates separates the skull from the brain .
- The cerebral ventricles are four anatomical cavities located in the brain that are interconnected with each other. Together they form the ventricular system in which the cerebrospinal fluid circulates.
- The ependymal canal is a conduit that runs through the entire spinal cord. It contains more than 140ml of the CSF from the body of an average individual. It occupies the center of the spinal cord, located in the center of the gray commissure and dividing it into an anterior and a posterior part.
Synthesis and pathway of the cerebrospinal fluid
Most CSF is created from blood plasma in the choroid plexuses of the cerebral ventricles. Once synthesized, it passes to the lateral ventricles, located in both cerebral hemispheres. Subsequently, through the interventricular holes, it reaches the third ventricle (located at the level of the diencephalon).
Eventually, it is reabsorbed into the venous system, in a passive process for which no energy is required. Under normal conditions, the LCR is reabsorbed very quickly, almost at the same rate as it forms in the choroid plexuses, which causes the intracranial pressure to always remain constant.
The cerebrospinal fluid renews itself at a rate that goes from 6 to 7 times a day and its average life cycle usually does not exceed 3 hours. When the pathways in which CSF circulates and accumulates in a compartment of the brain, hydrocephalus occurs. The immediate consequence is an increase in intracranial pressure.
Functions of the cerebrospinal fluid
The cerebrospinal fluid is one of the body fluids of our organism and its functions are very varied.
- It protects the central nervous system from possible trauma, shocks and collisions. It can be said that it is capable of amortizing intracranial movement up to 97%.
- It assumes a double biological function. On the one hand, of nourishment; since it takes care of transporting hormones, antibodies and lymphocytes to the nervous tissue. On the other hand, waste; since it discards the neuronal metabolic residues.
- It acts as an electrical insulator of the spinal cord.
- It allows to diagnose a series of neurological diseases, alterations of the meninges, subarachnoid hemorrhages or cerebro-spinal tumors.
- It is the gateway for epidural anesthesia.
As we see, cerebrospinal fluid is essential for maintaining and preserving the central nervous system. Small changes in its density or quantity can therefore generate serious consequences for brain functioning.
Bibliographical references
Zweckberger K, Sakowitz OW, Unterberg AW, et al. (2009). Intracranial pressure-volume relationship. Physiology and pathophysiology Anaesthesist. 58: 392-7.
