Attention! If this kind of liquid flows out of your nasal cavity, it may be that your brain is "leaking"

Tuchong Creative

In daily life, when we make mistakes accidentally, we often joke that we or our friends have "water in our brains". In fact, it is precisely because of "water in our brains" that our brains can function better.

Studies have shown that there is about 150 ml of "cerebrospinal fluid" in the human brain. This is a colorless and transparent liquid. The human brain is suspended and immersed in this cerebrospinal fluid, which not only ensures that the brain is not easily invaded by external toxic substances, but also limits the effects of some external hormones on the brain.

Cerebrospinal fluid flows in a directional manner in the human brain, from the ventricles to the cerebral aqueduct, to ensure the normal functioning of the brain. They flow into the third ventricle through the interventricular foramen, and then into the fourth ventricle through the cerebral aqueduct. The cerebrospinal fluid produced by the choroid plexus of each ventricle converges into the fourth ventricle and flows into the subarachnoid space of the brain and spinal cord through the median and lateral foramina of the fourth ventricle. Finally, the cerebrospinal fluid is infiltrated back into the superior sagittal sinus through the arachnoid granules beside the sagittal sinus, allowing the cerebrospinal fluid to flow back to the venous system. To put it in a more figurative way, the ventricles and the cerebral aqueduct can actually be regarded as "holes" and "pits" in the brain. There are four large "holes" in the brain, namely the first, second, third, and fourth ventricles, which are filled with "water". And there is another "pit" in the human brain that is similar to a sewer, which is the cerebral aqueduct, and the cerebrospinal fluid flows out of the brain through this "pit".

Cerebrospinal fluid is continuously produced and absorbed and flows back into the veins, playing the role of lymph in the central nervous system. It supplies certain nutrients to brain cells, transports metabolic products from brain tissue, and regulates the acid-base balance of the central nervous system. At the same time, it buffers the pressure on the brain and spinal cord, protecting and supporting them. It can also regulate intracranial pressure through circulation. For example, when the brain is undersupplied with blood, a reduction in cerebrospinal fluid can reduce intracranial pressure and increase blood supply.

Since there is really water in the human brain, can we be "brainwashed"? Does the brain cleaning system really change the water at night and shut down during the day like a road sweeper? "Brainwashing" is certain, but the scientific community has not yet reached a conclusion on the theoretical research on the brain's frequent "water changes" at night.

A new study published in Science in 2019 shows that something amazing happens in our brains every time we sleep: neurons first quiet down, and a few seconds later, blood flows out of the brain while cerebrospinal fluid flows in, "washing" our brains with rhythmic slow waves. The slow waves in neural activity help consolidate memory, while cerebrospinal fluid removes metabolic waste from the brain.

A study published in Nature in February 2024 also mentioned that when people are asleep, a large number of neurons will work together to generate waves with a frequency of about 40Hz, which promotes the entry of cerebrospinal fluid into the brain tissue and promotes the discharge of interstitial fluid carrying waste in the brain tissue, thereby removing various wastes that are harmful to the brain. We can simply understand this as the intracranial volume in the skull is fixed. When people are active, they need blood to supply oxygen, nutrition, etc. More blood will flow into the brain, which requires other fluids, namely cerebrospinal fluid, to flow out to compensate. During sleep, blood will flow out, and cerebrospinal fluid will enter the brain space to remove waste generated by daily activities.

However, in a newsletter published in Nature Neuroscience in May 2024, by directly measuring the clearance rate of metabolites in the mouse brain while awake, asleep, and anesthetized, it was found that the brain's clearance rate of substances is significantly reduced during sleep and anesthesia. This result is in stark contrast to previous research results, and it also suggests that excessive sleep can cause brain dysfunction. This challenges the traditional concept that "the core function of sleep is to clear toxins from the brain." Of course, scientific debates are common, and the question of the rate of "water change" during sleep remains to be determined. But whether it is "changing water" at night or during the day, its work on cleaning up impurities in the brain cannot be ignored.

Since cerebrospinal fluid is used to remove waste from the brain, we might assume that it is found only in the brain and spinal cord. In fact, the name is deceptive. This clear fluid, which cleanses, nourishes, and protects the surrounding organs, also bathes the body's nerves.

The latest research published in Science Advances in September 2024 pointed out that cerebrospinal fluid can actually penetrate all over the body. About two and a half years ago, the research team found in a surgical study that when they injected saline into the human cranial cavity, the peripheral nerves at the wrist also swelled. They injected finer tracer gold nanoparticles into mice for repeated experiments and found that smaller nanogold particles can spread to peripheral nerves throughout the body with cerebrospinal fluid, reaching as far as the sciatic nerve, and larger particles stay at the boundary between the spinal cord and the starting point of peripheral nerves. This study shows that small signal molecules, nutrients and even drugs floating in the cerebrospinal fluid can be delivered to the nerves. In the future, we may be able to use this new cerebrospinal fluid flow mechanism to design more precise treatment strategies for neurological diseases. For example, through the cerebrospinal fluid delivery system, specific drugs including painkillers can be directly applied to diseased peripheral nerves, avoiding the complex blood-brain barrier in traditional drug delivery methods. In addition, this discovery may also help us better understand the mechanisms of some neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Their occurrence may not only be related to lesions in the central nervous system, but the involvement of peripheral nerves may also play an important role.

In short, cerebrospinal fluid is not only the "guardian" of the central nervous system, it also maintains the health of peripheral nerves through a complex flow network. Although there are many difficulties in understanding the complex mysteries of the human body, with the tireless research and exploration of scientists, every small step from basic scientific research to clinical application in the future will be a big step forward in the continuation of life.

This article is a work supported by the Science Popularization China Creation Cultivation Program

Author: Chen Dingxin

Reviewer: Gui Yaxing, Chief Physician, Department of Neurology, Shanghai First People's Hospital

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.