In Bret Stetka’s book “A History of the Human Brain,” Santiago Ramon Y Cajal is quoted as saying,  “The brain is a world consisting of a number of unexplored continents and great stretches of unknown territory.”

This brief description describes our most complicated organ and, despite years of research, it continues to be most amazing.  

Composition

The human brain is composed of 86 billion neurons, with a thousand trillion connections that consist of vulnerable cells requiring  a protective environment to function properly.   

Neurons are cells within the nervous system that communicate with each other in unique ways. They are the basic working units of the brain, specialized cells designed to transmit information to other nerve cells, muscle or gland cells.

Most neurons have a cell body, an axon and dendrites. The cell body contains the nucleus and cytoplasm. The axon extends from the cell body and often gives rise to many smaller branches before ending at nerve terminals. Dendrites extend from the neuron cell body and receive messages from other neurons. Synapses are the contact points where one neuron communicates with another. The dendrites are covered with synapses formed by the ends of axons from other neurons.

Additionally, the brain must be protected by more than 400 miles of specialized vasculature designed to limit any substances that may come into contact with it.  The brain occupies the space of a quart container and weighs a total of about 3 pounds.  Those 3 pounds represent a mere 2% of the body weight for a 150-pound person, the quartful of brain, however, is so metabolically active that it uses 20% of the oxygen we take in through our lungs.  

To supply this much oxygen requires a high flow of blood. Fully 15% of the blood propelled into the aorta with each contraction of the left ventricle is transported directly up to the brain.  According to Sherwin Nuland, in his book “The Wisdom of the Body,” not only does the brain demand a large portion of the body’s oxygen and blood but it also begins its life requiring an equivalent share, or even more, of its genes.  

Of the total of about 50,000 to 100,000 genes in Homo sapiens, some 30,000 code for one or another aspect of the brain. Clearly, a huge amount of genetic information is required to create the human brain; the 1% of DNA in which we differ from the chimpanzee represents an enormity of genetic potential.

Unknowns

Assuming that each of our nerve connections encodes only one bit, which is certainly an underestimate, the capacity of our brain is on the order of 100 terabytes (about 1015 bits), or a hundred thousand times more than the information in our genome.  

The brain is so fascinating that scientists have yet to understand its entire function.  For example, while we do know that neurons communicate via synapses –  the small contact points at which chemical messengers transmit a stimulus from one cell to the next, we know little about the second type, the electrical synapse.   

There is little knowledge about where electrical synapses occur or how they influence the brain’s activity.  Scientists do know that an electrical synapse connects two neurons directly, allowing the electrical current that neurons use to communicate to flow from one cell to the next without a detour. This particular type of synapse occurs in the brain of every animal species studied so far.  Electrical synapses must therefore have important functions, but researchers just do not know which ones.  

Recently, however, researchers have used fruit flies to show that electrical synapses do not occur in all nerve cells, but in almost all areas of the brain.  By selectively switching off the electrical synapses in the area of visual processing,  they learned that the affected neuron’s reaction to certain stimuli are much weaker and without electrical synapses some nerve types become unstable and begin to oscillate spontaneously.

The results suggest that electrical synapses are important for diverse brain functions and can play very different functional roles, depending on the type of neuron. According to the report, electrical synapses are like the “dark matter”  of the brain.   The term dark matter is used by astronomers to describe the mysterious stuff that fills the universe but no one has ever seen. It emits no light or energy and thus cannot be detected by conventional sensors and detectors.  

Final Thoughts

The preface to Robert Ornstein and Richard F. Thompson’s book “The Amazing Brain” notes in part that it has taken thousands of years for people to understand the brain. Ancient Greeks thought it was like a radiator, to cool the blood.  In this century it has been compared to calculating machines, computers or  holograms.  None of these analogies are adequate, for the brain is unique in the universe, and unlike anything man has ever made. Scientists are still learning more about it.

Max Sherman is a medical writer and pharmacist retired from the medical device industry.  His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns.  He can be reached by email at  maxsherman339@gmail.com.