The big picture

Let’s get to know the architecture of our brain a little bit better. Although we talk about our grey mass, the brain actually isn’t grey, but a soft pink. The human brain has about the size of two clenched fists and on average weighs about 1300 grams. This weight varies between one person and the other, but a heavier brain does not indicate that its owner is more intelligent, as was presumed in the early days of brain research.

The brain consists of two parts: a right half and a left half, called cerebral hemispheres. The left hemisphere in principle governs the right side of the body and the right hemisphere the left side. Even though the two hemispheres are responsible for different parts of the body they do work together intensely all the time.

Both hemispheres contain the essential machinery for performing all tasks, but some specialisation has taken place during evolution. One of those specialisations concerns language. In almost all human beings, the left hemisphere is dominant where language is concerned. One of the specialisations of the right hemisphere concerns spatial manipulation.

The hemispheres are connected via the corpus callosum. This is a kind of master cable in the centre of your head made up of nerve fibres coming from both hemispheres. The corpus callosum makes information exchange between the left and right hemispheres possible.

It is possible to make a very detailed subdivision of both hemispheres. But the nice, coloured pictures from hemispheres with all the different parts you find on the internet haven’t got a lot to do with reality. Looking at the pulp on the counter in the research laboratory you can hardly find any subdivision. Watch a video on YouTube about dissecting brains and you will see what I mean.

Parts
In broad outlines, the brain can be divided into the following parts.

The cerebellum is like a small brain within the brain, seen here from the bottom side of the brain.  (© 7activestudio – Fotolia.com)

The cerebellum is like a small brain within the brain, seen here from the bottom side of the brain. (© 7activestudio – Fotolia.com)

The cerebellum, attached to the bottom of the brain, takes up only one eight of the total brain mass, but contains half of all neurons. That’s because it has a lot to do. Not only is the cerebellum important in coordinating movements and keeping balance, but it is also involved in learning, in language, and in working memory.

The brainstem is the oldest part of the human brain. It sits on top of the spinal cord and regulates among other things respiration, blood circulation, digestion, sleep cycle, and maintaining consciousness.

The diencephalon is situated between the cerebrum and the brainstem. It contains some interesting clusters of brain cells, like the thalamus and the hypothalamus. The thalamus is an intermediary station for information between the senses and the cerebral cortex. The hypothalamus controls body temperature, hunger, thirst, and heart rate.

The cerebrum is the large superior region of the brain. Its outer layer is called cerebral cortex. Thanks to its typical twists, it makes the brain look like a giant walnut. The cortex probably started twisting sometime during evolution. It makes more of the cortex’ neural tissue fit in the limited area of the skull. Only large mammals have a folded cortex. In smaller animals it has a smooth appearance.

The cortex can be divided into four lobes. The frontal lobe is the biggest lobe and can be considered the CEO of the brain. Within the frontal lobe, integration of information, reasoning, decision making, and planning and execution of movement are taking place. The parietal lobe is situated behind the frontal lobe and integrates sensory information. The occipital lobe is the smallest one and is located in the rearmost portion of the skull. It is the visual processing center. The temporal lobe is situated more or less below the other three lobes and contains important cell clusters like the hippocampus for memory and the amygdala for emotions. It comprises the audition and language centers as well.

Functional areas of the brainThe cortex can also be divided into different functional areas. The motor cortex is responsible for movement. The sensory cortex handles information from the senses. In the prefrontal cortex, all those important actions take place that make us feel human. It presides over our thought processes and is responsible for such things as planning, decision making and our social behaviour.

Some interesting numbers: the cortex varies in thickness between 1,5 and 4,5 millimeters. One cubic millimeter of cortex on average contains about 50,000 neurons, each of which has approximately 6,000 contacts with neighbouring cells. Although the brain only forms 2 percent of our total body weight, it uses 20 percent of blood and oxygen and 25 percent of all energy the body produces.

“The brain is for making decisions about how to enhance reproductive success, no more no less. A lot of other things come along for free.”
Michael Gazzaniga, neuroscientist

The architecture of the brain is laid down fairly definitive at birth. This does not vary greatly among individuals. But although all brains have the same general features, the connections between cells in the brain are unique. They reflect a person’s genetic make-up and life experience. Making new connections or losing unused ones is a lifelong process. Consequently, all brains are unique.

Images

Human brain anatomy © blueringmedia – Fotolia.com
Brain in motion © electrozebra – Fotolia.com
Functional areas of the brain © Alila Medical Media

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