The Human Nervous System may be divided into the Central Nervous System (CNS), comprising the Brain (composed mainly of Interneurons) and Spinal Cord, and the outlying Peripheral Nervous System (PNS). Each peripheral nerve is a bundle of axons. Some axons are extensions of motor neurons, which stimulate specific muscles or glands; others are part of sensory neurons, which convey information back to the CNS. Sensory neurons have their cell bodies clustered in ganglia, masses of nerve tissue that lie just outside the Spinal Cord.
Ganglia also contain the cell bodies of the motor neurons that make up the autonomic nervous system, a division of the PNS that controls the involuntary responses of glands and smooth muscles. Most internal glands (ie, the liver and pancreas) and most non-skeletal muscles (ie, heart muscle and the smooth muscles surrounding the digestive tract) are innervated by two classes - sympathetic and parasympathetic - of autonomic nerves: one class stimulates the muscle or gland and the other inhibits it.
The cell bodies of the motor neurons that stimulate voluntary muscles are located inside the CNS, in either the Brain or the Spinal Cord. However, most of the 10¹² neurons in the CNS are Interneurons.
Functions of the Central Nervous System (CNS)
are to gather, process, integrate, store, and abstract information about the internal milieu and extrapersonal environment. This work is accomplished by hierarchically organized neural interconnections that form the distributed cerebral networks. Hence, each portion of the nervous system performs specific functions. Many integrative functions are well developed in the Spinal Cord, and many of the subconscious functions of the CNS are originated and executed entirely in the lower regions of the brain. But it is the Neocortex that opens the world up for one's Mïnd.
Neurons
receive input from many interneuronal junctions (or synapses) on their dendrites and cell body. The resulting Neural Networks contain neurons whose output signal may be either excitatory or inhibitory to its recipient neuron. Although these Neural Networks are usually drawn as though they were solely within the Neocortex, many of the networks run from the Neocortex to the Thalamus or other subcortical structures such as the Hippocampus, the Corpus Callosum, and then back to the Neocortex. 
(See
Figure D )
Receptors
(those specialized proteins located on the post-synaptic membrane of neurons), are thought to consist of two components: a rod-like alpha-helix protein binder which grasps the neurotransmitter, and also an ionophore, which is the globular protein channel within the post-synaptic membrane that either opens and allows ions to flow, or enzymatically stimulates metabolic activity within the neuron, when such chemical binding occurs. 
This type of action consists of a series of biochemical processes that take place within the post-synaptic neuron which in turn, regulate ion flow or even change the number of receptors or may even change other structures within the neuron. The chemicals involved in these resultant biochemical processes are often called Second Messangers. These systems seem to contain the potential for modifying cells permanently, perhaps forming such activities as Neurological Memory and Learning.
(See
Figure A )
Synapses
established among neurons in a particular pattern become functionally connected to form a Cell Assembly or Neural Network. Once established, any neural network can be excited by others. If three neurons, (Alpha, Beta, and Gamma), are excited together, they become functionally linked together! Once linked together, this new Neural Network, (a system that was initially organized by a particular sensory event), is now able to continue its functional activity, even after the original stimulus has ceased (producing a form of Neurological Memory)!
Cell Memory:
To produce a permanent functional change in synaptic activity, the cell assembly must be activated repeatedly.
After the initial sensory event, this new cell assembly will reverberate.
Repeated reverberation within this new cell assembly will produce conditions which are suitable for permanent structural change.
In order for this permanent structural synaptic change to occur, there must be a time period in which the cell assembly is left relatively undisturbed.
Consolidation, (as this process of structural synaptic change is called) requires a minimal period of 5 to 10 minutes, and for major neurological events, up to one hour for optimal results.
For Long-Term Memory, the Hippocampus is especially important in this process. Once consolidation is completed, permanent Neural Networks are established!
These Neural Networks are engaged in Three Major Operations:
(1) Sensory Input
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The reception and registration of sensory stimuli from the outside and from within: such sensations as odors, tastes, touches, sights, and sounds originating from our external world, and those sensations of hunger, pain, proprioception, balance, and arousal from our internal world.
(2) Motor Output
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The planning and execution of complex motor acts, and reactions: such as the riding of a bicycle, dancing with a partner in time to music, ducking when an unexpected object flys overhead, and that "knee-jerk" response to painful stimuli.
(3) Intermediary Processing
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Those operations that are interposed between sensory input and motor output: Thought, language, memory, and self awareness, and even many aspects of mood and affect constitute different manifestations of what is referred to as Intermediary Processing (IP). The neural components for these processes are located primarily among the Interneurons of the Limbic System and Association Cortex.
IP increases the flexibility of behavior so that drives can be satisfied according to the limitations and opportunities that exist within the extrapersonal world.
The neural networks for much of this felxibility is provided by the interposition of Limbic and Association areas, between stimuli and responses, between Hypothalamic urges and our perception of external reality. These IP areas of the brain act as On-gates and Off-gates in a programming board.
Functional Cerebral Space:
Most of the interactions between neurons found in the layers of the Neocortex are with cells directly above or below, and with relatively less interaction with cells more than a couple of millimeters on either side. This is especially so in the Primary cortical zones of encoding. This vertical bias in cortical organization forms the basis for a second type of NeöCortical Organization: The Column!
The Neocortex is organized into narrow vertical columns which range from 0.5 to 1.0 millimeters wide. They run from the cortical surface to the white matter, in which each neuron in such a column is functionally similar to the others.
Afferent axons terminate on interneurons in Layer IV (Internal Granular Layer) and these interneurons transmit information vertically to synapse on other interneurons or pyramidal cell dendrites. Little information transfer occurs laterally, the primary direction of information travel being vertical. Physiological studies have shown that adjacent columns are maximally excited by different afferents, providing further evidence that each column functions as a
Mini Neural Network
The distance between cortical areas controlling different operations (for example, movement), which is reflected in the extent to which there is competition or cooperation when several operations are attempted simultaneously, is what is refered to as Functional Cerebral Space!
The upper levels of the CNS often operate not by sending signals directly to the periphery of the body but instead by sending signals to the control centers of the Spinal Cord, simply commanding the cord centers to perform their functions. The Brain Stem and Cortex can each independently influence the Spinal Cord to elicit movements, but they also have interconnections that permit them to mutually influence each other.
A Clear Example of this Intermediary Processing is as Follows:
Analgesia :
The human psyche can resist any pain! Hypnotically induced anesthesia, by the psychic manipulation of the nervous system, is on a continuum of diminishing bodily sensations with analgesia. Anesthesia refers to a complete or near complete elemination of sensation in all or part of the body. Analgesia refers only to a reduction in the sensation of pain, allowing associated sensations of pressure, temperature, position, etc. The Neocortex plays an important role in interpreting the quality of pain. However, pain perception is a function of the lower centers, namely, the Reticular Formation , Thalamus, and the lower dorsal spinal roots.
Pain receptors (Nocioreceptors) are free nerve endings. Unlike most of the other sensory receptors of the body, the pain receptors do not adapt of stimulation. As a matter of fact, the threshold for excitation of these fibers becomes progressively lower and lower as the pain stimulus continues! They are widespread in the superficial layers of the skin and in some internal tissues such as arterial walls, joint surfaces, periosteum, and the falx and tentorium of the cranial vault. These receptors are sensitive to mechanical or thermal stimuli that arise near levels that may produce damage to the tissue. Also some of these nerve fibers react to chemical stimuli.
Most localization of pain results from simultaneous stimulation of tactile receptors along with the pain stimulation. For pain sensation, a transduction step is thought to occur between the damaged tissue, (source of the pain), and neural activation. The damaged tissue releases a chemical called a Neurokinin, which is thought to act like a neurotransmitter to activate pain fibers. Once activated, the impulse is transmitted to the dorsal horn of the spinal cord, where it is ultimately transmitted to the Neocortex.
The brain itself is capable of controlling the degree of input of pain signals to the nervous system by activation of the pain control system called the Analgesia System ! Hypnotically induced anesthesia enhances the release of Endorphins (those morphine-like substances) known to be present in the mid-Thalamic areas of the brain.
(See Figure G!)
The Analgesia System
involves three distinct areas of the Central Nervous System:
- The PeriAqueductal Gray Area:
Located in the Mesencephalon and upper Pons surrounding the Aqueduct of Sylvius. Neurons from this area send their signals to;
- The Raphé Magus Nuclei:
These are very thin midline nuclei located in the lower Pons and upper Medulla. From here the signals are transmitted down the spinal cord to;
- A Pain Inhibitory Component:
located in the dorsal horns of the spinal cord. At this location the pain signals can be blocked before they are relayed on to the brain!
Stimulation in either the PeriAqueductal Gray Area or in the Raphé Magnus Nuclei can almost completely supress pain signals from the dorsal spinal roots!
Several Neurotransmitters are involved in the Analgesia System, especially enkephalin and serotonin. Many of the fibers of both the PeriVentricular Nuclei and PeriAqueductal Gray Area secrete enkephalin at their endings. The Raphé Magus Nuclei send fibers to widespread areas of the diencephlon and spinal cord. The fibers that originate in the Raphé Magnus Nuclei and terminate in the dorsal horns of the spinal cord secrete serotonin at their endings. The serotonin subsequently acts upon yet another set of local spinal cord neurons that are thought to secrete enkephalin; causing inhibition of the incoming presynaptic pain fibers to the neurons on the dorsal horns.
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