The active components of the nervous system are the neurons. Neurons allow for the conveyance and processing of information; information derived from the body’s various senses, with corresponding control responses derived from this information being formulated by collections of neurons either in the spinal cord or in the brain, and then directed outward towards the body’s motor and other support systems. The mechanisms effected by neurons form an organic equivalent to an extremely complex electrical circuit. Taking a very simplistic view, it can be observed that specifically, they roughly correspond to an analogue circuit that provides the operations of a diode, an amplifier and a band-pass filter; along with a wealth of processing and memory capacity. One uses such components in the purely mechanical world to form an analog computer. Further, from a digital computer standpoint, these are necessary elements for gates and switches, which are essential to the logic operations of such computers. As a basic characteristic of its physical makeup, an individual neuron allows for the conveyance of electro-chemical representations of information in only one direction through the cell. In a more general computer network configuration, we would refer to this as a simplex communication channel. So, how is this generally useful facility realized?

In a most simple overview, a neuron cell is comprised of three main components enclosed within a common membrane: a cell body called the soma, a collection of appendages called dendrites and another appendage termed an axon. There is, in general, only one axon per neuron cell, while there may be many dendrites. The dendrites are the input channels for information into the cell while the axon is the output channel. In its steady state, a neuron builds up a net electrical charge across the membrane which defines the boundary of the cell. This membrane is an insulator, composed of lipid molecules with modulated ion channels that pass through it. Through these channels, the neuron pumps sodium ions out of the cell and potassium ions into the cell resulting in a small negative potential when measured on the inside of the membrane relative to the outside of the membrane. Given a chemical stimulus through the dendrites, the neuron can evoke an electrical discharge that is termed an action potential; a process very similar to an electrical capacitor’s discharge. The discharge originates at the axon hillock where the axon meets the soma. This action potential is then propagated along the axon of the cell. At the axon’s terminus, the electrical impulse can be conveyed to a different neuron through a very interesting chemical, not electrical, mechanism termed a synapse.

Two neurons can be physically connected when an axon extension from one neuron, the pre-synaptic neuron, becomes permanently attached to a different neuron, the post-synaptic neuron. The connection point can occur at any location on the post-synaptic neuron: on its dendrites to form an axodendritic synapse, on its soma forming an axosomatic synapse or on its axon forming an axo-axonal synapse. The axon from one neuron can make many connections to a single post-synaptic neuron and it can make connections to many different post-synaptic neurons. The attachment point of one of these axon connection points, called a terminal button, to a post-synaptic neuron is a synapse and the space between the pre-synaptic and post-synaptic boundaries is called the synaptic cleft. So, for any collection of neurons, the number of synapses can be much larger than the total number of neurons. The total information handling capacity, a characteristic directly related to the cognitive capacity of the brain, appears to be related to the number of active synapses in the brain.

At a synapse connection, some rather complex operations are activated through which information is passed from one neuron to another. An action potential within a neuron, when it reaches the terminal button of the axon, causes the release of one or more of a variety of chemicals termed neurotransmitters. Neurotransmitters are able to cross the synaptic boundary to the post-synaptic neuron. As regulated by this post-synaptic neuron, the neurotransmitter material may tend to

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