Protect and serve

A lot of attention has been given lately to the brain in sports. A heated debate about possible health effects of concussions on American football players has been going on for years. Until finally, the National Football League acknowledged that many of its ex-players are suffering from chronic traumatic encephalopathy, a progressive, degenerative brain disease.

It is clear, the brain is very vulnerable. But it is also the best protected organ of our body. Mother Nature has taken a lot of precautionary measures. To begin with, the brain has been wrapped in a very firm skull that can withstand considerable blows. The skull is made up of 22 different bone parts.

The meninges consists of three membranes. (courtesy The brain from top to bottom)

The meninges consist of three membranes. (courtesy The brain from top to bottom)

Second in the line of fire are the meninges, mainly known for the sometimes deadly infection called meningitis. The meninges consist of three membranes that form a flexible, structural, but semipermeable protective pad that completely surrounds the central nervous system.

The next line of defence is the ventricular system. This system is made up of four interconnected cavities: two lateral ventricles, one in the centre of the brain, and one in the brainstem.The ventricular system has two protective functions. It provides an additional structural fluid cushion. It also offers physiological protection via its immunologic functions and its waste disposal system.

The ventricles are filled with fluid, called cerebrospinal fluid. This fluid circulates through the ventricles and around brain and spinal cord. It provides a mechanical cushion to protect the brain from impact with the skull when the head moves. It also allows the brain to float, thus preventing gravity from pushing down the brain upon the lower side of the skull, which would cause serious damage.

The ventricular system is made up of four interconnected cavities filled with cerebrospinal fluid. (courtesy The brain from top to bottom)

The ventricular system is made up of four interconnected cavities filled with cerebrospinal fluid. (courtesy The brain from top to bottom)

Cerebrospinal fluid is important in maintaining a constant environment for brain cells. When it enters the blood stream after having circulated, it takes with it waste from brain metabolism The total volume of cerebrospinal fluid is estimated at 150 millilitres. Special cells in the ventricular system produce this fluid. The production may lay around 500 millilitres per day.

Rigid
The totality of brain mass, blood vessels, and ventricular system has to fit within the available space of our skull. The skull is an absolute, rigid entity. If one part of its contents enlarges another part has to give in. An extension of the totality is not possible. This could lead to problems. An overproduction of cerebrospinal fluid for instance has to be drained via a medical intervention, otherwise brain substance would die.

To make up for changes, the ventricular cavities will expand or contract. The brain shapes the ventricular system. Any changes in the anatomy of the brain can distort the ventricular system and influence ventricle size and shape. When for instance the brain mass deteriorates the ventricles enlarge to fill in the void.

Thus the size of the ventricles can be an indicator of the health of the brain. Ventricle volumes are extremely diverse between individuals. In general, the ventricles tend to slowly become bigger during ageing. In men, this process starts as of their 40s, in women as of their 50s.

An adequate blood supply is vital to the brain. Too much blood in our head will raise blood pressure and may cause damage to brain cells, but too little blood could also cause the death of brain cells. Although our brain generally comprises only two percent of our total body weight, it sucks up twenty percent of blood supply, which the heart is pumping around. Blood brings oxygen and nutrients to the brain and takes away waste produced during metabolism in the brain.

615px-Cerebral_vascular_territoriesThe regulation of the blood flow is a complex train of events involving among other things vascular cells and neurones. Blood flow to the brain is tightly coupled with the metabolic demand of local neurones. An increase in neuronal activity leads to an increase in regional cerebral blood flow. Almost instant adjustments are possible. When neurones are doing overtime, they need extra blood for the delivery of nutrients and for the removal of garbage.

Scientists made clever use of this fact. When a group of brain cells is activated and more blood flows to that part of the brain, it will show up on a brain scan. Thanks to these scans, in a short period our knowledge of the brain has grown exceptionally. Researchers make volunteers carry out certain mental tasks while they are inside the scanner. The scans show the parts of the brain where more blood flows to due to extra activity. Thus certain parts of the brain can be linked to certain mental tasks.

Barrier
Our heart pumps blood through our entire body. The blood that flows through our brain has also been in other parts of our body. Therefore it is not only good things the blood might bring to the brain. Harmful substances end up in our blood via for instance our food or the air we breathe in. Generally, our immune system is perfectly capable to put these intruders out of action. But in our brain, many of these substances would cause havoc. So it is a matter of life and death these particles don’t reach the brain.

The blood-brain barrier is made up of special cells that filter out unwanted substances. (© Armin Kübelbeck - Wikipedia)

The blood-brain barrier is made up of special cells that filter out unwanted substances. (© Armin Kübelbeck – Wikipedia)

To counteract unwanted intrusion into the brain the blood-brain barrier came into being. This barrier makes sure the brain is well-separated from the rest of our body. Special cells let blood and its useful contents pass, but filter out any other substances. Thus the blood-brain barrier maintains a stable environment for neurones to function effectively.

The blood-brain barrier protects the brain this way, but at the same time is a hurdle medical science has to take. That’s because the well-functioning barrier also bans substances doctors would love to see entering the brain. Pharmaceuticals that have been developed specifically to help cure brain diseases usually can’t pass the blood-brain barrier either.

For example, one of the problems of Parkinson disease is that the brain produces too little dopamine, a substance that activates certain brain cells. An injection of dopamine would then of course be very useful. Unfortunately, this injected dopamine is blocked by the blood-brain barrier and doesn’t reach the place where it would be needed. Clever biologists discovered that another substance, levodopa, is able to pass through the blood-brain barrier. Levodopa is the raw material for dopamine. When someone is taking pills containing levodopa, this substance will reach the brain and on the spot is being turned into dopamine.

Conquering the blood-brain barrier is one of the biggest challenges for researchers developing drugs for neurological diseases. The barrier is a significant obstacle to drug therapy since the influence of chemical substances depends on how easily they pass through the barrier.

Unfortunately, the skull can't protect the brain from repeated strong blows. (© 7activestudio - Fotolia.com)

Unfortunately, the skull can’t protect the brain from repeated strong blows. (© 7activestudio – Fotolia.com)

Researchers have high expectations of nanotechnology. This technique is directed toward the fabrication of minuscule particles called nano-particles. These particles might be suitable to function as tiny vehicles to help transfer drugs across the blood-brain barrier and deliver the healing substances exactly to the desired spot.

Despite all the above mentioned protective measures, the brain still can easily be damaged. Repeated smacks and blows will make the damage permanent and progressive. So, wouldn’t it be high time to stop thinking of boxing as a sport?!

Image

Riot police © mario beauregard – Fotolia.com
Concussion damage © Alila Medical Media
Cerebral blood flow © Frank Gaillard – Wikipedia

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