Self Comes to Mind

has three main anatomical elements: (1) the cell body , which is the cell’s powerhouse and includes the cell nucleus and organelles such as mitochondria (the neuron’s genome, its complement of governing genes, is located within the nucleus, although DNA is also to be found within mitochondria); (2) the main output fiber, known as the axon , which arises from the cell body; and (3) input fibers, known as dendrites that stick out from the cell body a bit like antlers. Neurons are connected to one another via a border area called the synapse . In most synapses the axon of one neuron makes chemical contact with the dendrites of another.
    Neurons can be active (firing) or inactive (not firing), “on” or “off.” The firing consists of producing an electrochemical signal that crosses the border to another neuron, at the synapse, and makes that other neuron fire too, provided the signal meets the requirements of the other neuron to fire. The electrochemical signal travels from the neuron’s body down the axon. The synaptic border is located between the end of an axon and the beginning of another neuron, generally at the dendrite. There are several minor variations and exceptions to this standard description, and different kinds of neurons vary in shape and size; but this outline is acceptable as far as the big picture goes. Each neuron is so small that one needs the major amplification of a microscope to see it, and in order to see a synapse one needs an even more powerful microscope. Still, smallness is relative, entirely in the amplified eye of the beholder. Compared to the molecules that make them up, neurons are truly gigantic creatures.
    When neurons “fire,” the electric current known as the action potential is propagated away from the cell body and down the axon. The process is very fast—it takes only a handful of milliseconds, which should give an idea of the remarkably different time scales of brain and mind processes. We need hundreds of milliseconds to become conscious of a pattern presented to our eyes. We experience feelings in a time scale of seconds , that is thousands of milliseconds, and minutes .
    When the firing current arrives at a synapse, it triggers the release of chemicals known as neurotransmitters (glutamate is an example) in the space between two cells, the synaptic cleft. In an excitatory neuron, the cooperative interaction of many other neurons whose synapses are adjacent and that release (or do not) their own transmitter signals, determines whether the next neuron will fire, that is, whether it will produce its own action potential, which will lead to its own neurotransmitter release, and so forth.
    Synapses can be strong or weak. Synaptic strength determines whether and how easily impulses will continue to travel into the next neuron. In an excitatory neuron, a strong synapse facilitates impulse travel, while a weak synapse impedes or blocks it.
    One critical aspect of learning is the strengthening of a synapse. Strength is translated into ease of firing and thus ease of activation of the neurons downstream. Memory depends on this operation. Our understanding of the neural basis of memory at neuron level can be traced to the seminal ideas of Donald Hebb, who, in the mid–twentieth century, first raised the possibility that learning depended on the strengthening of synapses and the facilitation of the firing of subsequent neurons. He did so on a purely theoretical basis, but his hypothesis was subsequently proven correct. In the past few decades the understanding of learning has deepened to the level of molecular mechanisms and gene expression.
    On average each neuron talks to relatively few others, not to most, and never to all. In fact, many neurons talk only to neurons that are close by, within relatively local circuits; others, even if their axons travel for several centimeters, make contact with only a small number of other neurons. Still, depending on where the neuron sits in the overall architecture, it may have more or fewer partners.
    The billions of neurons are organized in circuits. Some are very small microcircuits, truly local operations invisible to the naked eye. When many microcircuits are placed together, however, they form a region, with a certain architecture.
    The elementary regional architectures come in two varieties: the nucleus variety and the cerebral cortex patch variety. In a patch of cerebral cortex, the neurons are displayed on two-dimensional