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The Brain Primer

© John McManamy

"There may be anywhere between 100 trillion and a quadrillion synapses organized into elaborate networks that account for the brain's vast complexity."

This is the first of three articles based on the Surgeon General's Report on Mental Health:

It's like a building being demolished. Billions of neurons seem to overload, shorting an infinity of circuits which triggers the collapse of the superstructure we know of as the brain. Buried beneath the rubble like the mangled victim of an earthquake is an entity we call the mind, somehow just managing to cling to life but despairing of ever finding a way out.

What really goes on in the brain during a depressive episode?

No one actually knows, but last week the Surgeon General provided us with a fairly useful primer in his Report on Mental Health. The brain, in the words of the Surgeon General, is "the great synthesizer" of the many biological, psychological, and sociocultural phenomena that make us who we are, the product of our genes and experience working together.

The brain is a three-pound mass containing some 100 billion nerve cells - neurons - thousands of different kinds, each forming more than a thousand synaptic connections with other neurons. In all there may be anywhere between 100 trillion and a quadrillion synapses organized into elaborate networks that account for the brain's vast complexity.

Just to give you an idea of how truly complicated the brain is, of 35,000 genes in the human genome, some half to three-quarters of these go into the brain's makeup.

So what happens when someone - say a little man inside - decides to throw a switch? To start, signals from the neuron travel out a single extension called the axon that may end in several terminals. These signals are picked up by branches - dendrites - extending from other neurons.

Communication occurs at specialized structures called synapses, organized into two parts for sending and receiving. The presynaptic structure is located on a terminal portion of the sending neuron that contains packets of sending chemicals, or neurotransmitters. The postsynaptic structure on the receiving neuron has receptors for these molecules.

There are two main types of molecules that function as neurotransmitters: small molecules - including dopamine, serotonin, and norepinephrine - and larger molecules that are essentially protein chains. All told, there are some 100 neurotransmitters in the brain. According to the Report:

"A neurotransmitter can elicit a biological effect in the postsynaptic neuron by binding to a protein called a neurotransmitter receptor. Its job is to pass the information contained in the neurotransmitter message from the synapse to the inside of the receiving cell."

The copyright of the article The Brain Primer in Depression is owned by John McManamy. Permission to republish The Brain Primer in print or online must be granted by the author in writing.