CEREBROSPINAL FLUID: CHARACTERISTICS, CIRCULATION, FUNCTION - NEUROPSYCHOLOGY - 2025

The cerebrospinal fluid or cerebrospinal fluid is an aqueous liquid, transparent and colorless flowing in the central nervous system. It is made up of potassium, sodium, chlorine, calcium, inorganic salts (phosphates) and organic components such as glucose. It has several functions, such as protecting the brain against shocks and maintaining an adequate metabolism.

Cerebrospinal fluid flows through cavities that exist in the brain called cerebral ventricles, through the subarachnoid space, and through the ependymal duct (in the spinal cord).

The amount of cerebrospinal fluid that circulates in a healthy person is between 100 and 150 ml, being produced continuously reabsorbed. When there is more production than absorption, the pressure of the cerebrospinal fluid rises, leading to hydrocephalus.

It can also happen that the pathways that contain this fluid become blocked, causing it to accumulate. On the contrary, it is also possible that there is a decrease due to some type of leakage or extraction, which would cause headaches (severe headaches).

How does cerebrospinal fluid originate?

The cerebrospinal fluid circulating in the subarachnoid space that surrounds the brain and spinal cord. Source: User: Textbook OpenStax Anatomy and Physiology CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0) via Wikimedia Commons)

70% of the cerebrospinal fluid originates from the choroid plexuses, small vascular structures that have a large number of capillaries. Blood plasma leaks into these organs to form cerebrospinal fluid. There are choroid plexuses in all four ventricles, but mainly in the two lateral ventricles.

However, the remaining 30% of this fluid is produced in the ependyma, which comes from the arachnoid membrane. To a lesser extent, they also come from the brain itself, specifically from the perivascular spaces (around the blood vessels).

The cerebrospinal fluid is renewed every 3 or 4 hours, producing a total of about 500 ml per day.

The 150 ml of cerebrospinal fluid that an adult has, are distributed as follows: about 30 ml circulates in the lateral ventricles, 10 ml in the third and fourth ventricles; subarachnoid space and cerebral cisterns, 25ml; and 75 ml in the spinal subarachnoid space. However, its volume varies according to age.

Circulation and reabsorption of cerebrospinal fluid

Cerebrospinal fluid flows through the ventricular system of our brain. This consists of a series of cavities that are found inside the brain.

Once secreted, this fluid circulates from the lateral ventricles to the third ventricle through the interventricular foramen of Monro. The cerebrospinal fluid then reaches the fourth ventricle through the aqueduct of Silvio. The fourth ventricle is the one located at the back of the brain stem.

To enter the subarachnoid space, the fluid must pass through three openings: the median opening and the lateral ones. They are also called the orifice of Magendie and the orifices of Luschka. As it passes through these orifices, the liquid reaches the cisterna magna and, later, the subarachnoid space. This space covers the entire brain and spinal cord. Cerebrospinal fluid reaches the latter through the cerebral obex.

As for the reabsorption of cerebrospinal fluid, it is directly proportional to the pressure of the fluid. That is, if the pressure increases, so does the reabsorption.

Fluid circulates from the subarachnoid space into the blood to be absorbed through structures called arachnoid villi. These connect with venous sinuses that have a membrane that covers the brain called the dura mater. These sinuses are directly linked to the bloodstream.

However, some authors have suggested that the fluid can also be reabsorbed into the cranial nerves through lymphatic channels. It seems that they are essential especially in newborns, in which the arachnoid villi are not very well distributed yet.

On the other hand, there is another hypothesis that states that cerebrospinal fluid does not flow unidirectionally, but depends on more factors.

Furthermore, it could be continuously produced and absorbed due to the seepage and reabsorption of water through the capillary walls into the interstitial fluid of the surrounding brain tissue.

Features

Cerebrospinal fluid has several important functions, such as:

Protect the central nervous system

This fluid, together with the meninges, has a cushioning function within the skull. In other words, it reduces external impacts. Thus, in the face of any blow or contusion, it makes it less likely that a part as delicate as our brain will suffer damage.

Maintain internal homeostasis

It allows the circulation of neuromodulatory substances. These substances are very important for the regulation of vital functions, and consist of hypothalamic and pituitary hormones and chemoreceptors.

Immune protection

On the other hand, it also protects the central nervous system from external agents that could cause illness. In this way, it performs an immune protection that is also necessary in this part of our body.

Waste excretion

The unidirectional circulation of cerebrospinal fluid into the blood allows the brain to ward off potentially harmful substances. For example, dangerous drugs and metabolites.

Nutrition

Since the ependymal tissue and the pia mater and arachnoid layers of the brain are avascular (blood does not circulate through them), they do not receive nutrients from the blood. However, as the cerebrospinal fluid communicates with the vascular system, it can capture the nutrients that are there and transport them to these tissues.

Maintain adequate pressure

Cerebrospinal fluid flows to compensate for changes in intracranial blood volume that can occasionally occur. In this way, it maintains a constant intracranial pressure.

Buoyancy

The weight of the human brain is between about 1200 and 1400 grams. However, its net weight suspended in the cerebrospinal fluid equals 25 grams.

Therefore, the brain has a neutral buoyancy that allows it to maintain its density without being affected by its own weight. If it were not surrounded by fluid, blood could not flow properly through the brain. As a consequence, the neurons located in the lower part of it would die.

Cerebrospinal fluid extraction

In a lumbar puncture, a needle is placed through the dura (shown in red) to reach the CSF. The needle creates a hole in the dura.

Cerebrospinal fluid can be obtained through three different methods: lumbar puncture, cisternal puncture, and ventricular puncture. The last two require surgical intervention and are much less common.

The main reason for the removal of cerebrospinal fluid is for medical examinations. Professionals examine characteristics of the liquid such as its color, pressure, protein level, glucose level, number of red or white blood cells, gamma globulin level, etc. The purpose is to evaluate the existence of certain neurological conditions.

4 vials of normal-appearing human cerebrospinal fluid collected by lumbar puncture. Source: James Heilman, MD CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) via Wikimedia Commons)

Some of those that can be detected are hydrocephalus, infections such as meningitis, brain lesions, spinal cord damage, multiple sclerosis, Guillain-Barré syndrome, encephalitis, epilepsy, metabolic dementia, pituitary tumor, Reye's syndrome, etc.

On the other hand, lumbar puncture can also have a therapeutic use. It can be done to inject other substances such as analgesics, antibiotics, anti-inflammatories, etc.

For the lumbar puncture, local anesthesia will be applied and then a needle will be inserted into a specific part of the lower back.

In the cisternal, the existing fluid in the cisterna magna will be extracted by introducing the needle under the occipital bone (in the posterior area of ​​the skull).

As for ventricular puncture, it is carried out very rarely and in people in whom the existence of a brain herniation is suspected. To do this, an incision is made in the skull and the needle is placed inside one of the brain ventricles.

Cerebrospinal fluid disorders

Various cerebrospinal fluid abnormalities can reflect different diseases. Analyzing it, it is possible to diagnose conditions such as bleeding, infections, certain syndromes, etc.

Cloudy cerebrospinal fluid

When the cerebrospinal fluid looks cloudy, it means an increase in the number of its cells. That is, it may indicate an accumulation of white blood cells or proteins.

When there are more white blood cells than necessary, the body may be trying to defend itself against an infection such as meningitis, or a sign of a demyelinating disease.

If there is more protein than necessary, it can be a sign of diabetes, tumors, injury, infection, or inflammation.

Cerebrospinal fluid color

If the color of the fluid is reddish, there may be some kind of bleeding or obstruction in the spinal cord. However, this blood can come from the prick itself that is carried out in the lumbar puncture test.

On the other hand, when there is an increase in protein or bleeding for more than three days, the fluid appears yellow, orange or brown.

Changes in cerebrospinal fluid pressure

An increase or decrease in the pressure of this fluid is the cause of certain medical conditions.

When the pressure of the cerebrospinal fluid is very high, it is called intracranial hypertension since it produces an increase in cranial pressure. In this way, the ventricles dilate and the brain tissue is tight, which can lead to poor blood circulation and injury.

Sometimes it occurs spontaneously, while at other times it is triggered by other conditions such as: brain tumors, strokes, blood clots in the brain, lupus, sleep apnea, certain medications such as lithium, etc.

The main symptoms it causes are severe headaches, ringing in the ears, visual disturbances, difficulties in doing daily tasks and neurological problems.

In contrast, low cerebrospinal fluid pressure can cause headaches. In fact, it is not uncommon for it to occur after lumbar extraction. So to prevent it, the patient is asked to rest for 24 hours after the test.

Another cause is the appearance of a fistula of the cerebrospinal fluid, which allows its escape. It usually appears spontaneously, traumatic, or surgically; although it is also associated with infections and tumors.

Altered glucose levels in the cerebrospinal fluid

Simply put, if high or low levels of glucose (sugar) appear in the fluid, it is a reflection that there is more or less glucose than the account in the blood.

A low level of glucose in this fluid can also indicate infections such as meningitis, or tuberculosis.

Elevated gamma globulin levels

When these levels increase in the cerebrospinal fluid, it can be a sign of the presence of diseases such as: multiple sclerosis, Guillain-Barré syndrome or neurosyphilis (consequences of syphilis without treatment for more than 10 years).

References

1. WHAT IS INTRACRANIAL HYPERTENSION? (HIC). (sf). Retrieved on November 21, 2016, from the Intracranial Hypertension Research Foundation.
2. Cerebral spinal fluid (CSF) collection. (sf). Retrieved on November 21, 2016, from MedlinePlus.
3. Cerebrospinal fluid. (sf). Retrieved on November 21, 2016, from Wikipedia.
4. Chudler, E. (nd). The Ventricular System and CSF. Retrieved on November 21, 2016, from the University of Washington.
5. Definition of Cerebrospinal fluid. (sf). Retrieved on November 21, 2016, from MedicineNet.
6. García, MS, Pérez, PC, & Gutiérrez, JC (2011). Cerebrospinal fluid and circulation disorders: hydrocephalus, pseudotumor cerebri, and low blood pressure syndrome. Medicine-Accredited Continuing Medical Education Program, 10 (71), 4814-4824.
7. Hajdu SI (2003). "A note from history: discovery of the cerebrospinal fluid". Annals of Clinical and Laboratory Science. 33 (3): 334–6.
8. Noback, C.; Strominger, NL; Demarest RJ; Ruggiero, DA (2005). The Human Nervous System. Humana Press. p. 93.
9. Saladin, K. (2007). Anatomy and Physiology: The Unity of Form and Function. McGraw Hill. p. 520.