Brain Development

Brain Development

Anatomy and physiology are not glamorous subjects – a complete knowledge of them requires careful and intensive study. But the provide the very bedrock of the subject matter. It is easy to overlook the fact that the brain is, after all, just an organ. It is an organ like the liver or the spleen or the stomach. Like these other organs of the body, it is made of cells. These cells are connected together to form a piece of tissue with a certain characteristic texture and shape, and so the brains of all of look roughly the same. And yet, there is something almost miraculously special about this organ: it is the organ of the mind – indeed, of our very selves.

Despite this unique property of the brain, its cells are not fundamentally different from the cells of other bodily organs. What is the prototypical nerve cell? It consists of three basic parts. The first, the cell body, contains essentially the same things found in cells in other organs – namely, the things that govern its basic metabolism. There are two types of appendages to this cell body, one of which is known as the dendrites, the other as the axon; in our prototypical nerve cell, there are many dendrites but only a single axon. Together, these three components form the typical structure of a brain cell – a neuron. Neurons (in conjunction with some supporting cells called glia) are all that the nervous system is made of – billions and billions of cells, connected up with one another.

This interconnection takes place as follows: The axon of one neuron links up with a dendrite of another neuron, whose axon in turn links with a dendrite of another neuron, and so on; multiple interconnections can occur, as each dendrite on a neuron can accept many axon terminals. At the place where two cells link up – between the axon of one cell and a dendrite of the other – there is a minute gap, called a synapse. Over the synaptic gap, small chemical molecules pass from one neuron to the next; these molecules are called neurotransmitters. This transmission of chemical is the principal means of communication between the cells of the brain. Different cells located in different brain regions use different types of neurotransmitters.

A living creature, and especially a human being, is first and last a subject, not an object. Photo by Elena.

These five concepts – cell body, dendrite, axon, synapse, neurotransmitter – are all that one really need to know about neurons as basic concepts.

What is it, then, that makes this organ so unique – how is it that these interconnected cells produce something as miraculous as our awareness of being in the world? How can it be that the physiological activity of these cells, comprising this lump of tissue, produces something so utterly unlike anything that any other organ produces – indeed, so utterly unlike anything else in the physical universe?

Although the elementary properties of neural tissue obviously do not explain how or why the brain produces subjective awareness, there are two features about it that are quite unusual. These features are not fundamental, but they do distinguish the cells of the brain from those of most other bodily organs. The first distinguishing feature of neurons is the nature of the links between them: the synopsis mediated by neurotransmitters. This linkage permits the passing of “information” from one cell to another. The principle of information transfer is not unique to nerve cells (other cells also interact with each other in various ways), but the dedicated function of communication between nerve cells is an important distinguishing feature.

The second outstanding feature of brain tissue is that, while the basic plan of the brain's organization is, as it were, predetermined by our genes, the overall plan is dramatically modified by environmental influences during life. The brain comes into the world with innumerable potential patterns of detailed organization, as reflected in the infinite combinations through which its cells could connect up with each other. The precise way that they do connect up, in each and every one of us, is largely determined by the idiosyncratic environment in which each brain find itself. In other words, the way our neurons connect up with each other depends on what happens to us. Modern neurons connect up with each other depends on what happens to us.

Modern neuroscience is becoming increasingly aware of the role played in brain development by experience, learning, and the quality of the facilitating environment – and not only during childhood. In short, the fine organization of the brain is literally sculpted by the environment in which it finds itself – far more so than any other organ in the body, and over much longer periods of time.

At the level of neural tissue, then, these two features – the capacity for information transfer and that for learning – are what most distinguishes the brain from other organs. These capacities are present far more potently in brain tissue than in any other tissue of the body.

Neuropsychology, like classical neurology, aims to be entirely objective, and its great power, its advances, come from just this. Illustration by Elena.

The Brain and the Inner World, Introduction to Basic Concepts. Mark Solms, Oliver Turnbull.