Synaptic Formation
AT THE DISTAL END OF EACH AXON and its collateral branches are very fine terminations called Teleodendria. These Teleodendria are covered with small knobs, called Terminals, which make interneural junctions with other cells. Electrical impulses arising from within the cell body (or Soma) travel through the axon to a specialized terminal known as the Synapse.
In the animal kingdom there are basically two types of synapses: 1) the chemical synapse, and 2) the electrical synapse. 
Synaptic formation occurs concurrently in all cortical layers and in all cortical areas. In humans, synaptic density is thought to increase continually until about 2 years postnatally. After this point 50% of the synapses are lost by 16 years of age. The process of loss of these synapses is referred to as shedding. These observations suggest that if experiences alter synapses during development, they do so by influencing their survival, rather than by regulating their initial formation. 
Any given brain region will send axons to only a limited number of other regions, and the synapses are made only on a specific part of certain cells within that region. Synapses close to the Axon Hillock may influence cell firing because of their proximity. Inhibition or excitation by the more distal axosynaptic connections may allow for some subtle control of intercellular communication. Some synapses may also change structurally with use or disuse, thus becoming increasingly or decreasingly effective in communication. The locations to synapses are determined in part by genetic instructions, in part by the orientation of the cell where the axons arrive, in part by the timing of axonal arrival (axons apparently compete for available space), and in part by the use they are given once a connection is made. In addition, the pharmacology of the synapse is flexible.
Neurons have an electrical charge across their membranes.
If a neuron is undisturbed, the charge remains relatively constant. Each neuron is seperated from actual physical contact with every other neuron and, as a result the electrical impulses generated within the nerve cell cannot jump the gap to the next neuron. Therefore, communication across this seperation uses a special "language" that is dependant upon the release of a various specialized chemical substances as they depolarize. With few exceptions, it is believed that each neuron releases only one type of chemical substance (referred to as a Neurotransmitter), and that it releases this same substance at all of its seperate terminals.
The axonal terminal is separated from other neurons by a very small space called the Synaptic Cleft. The membrane of the axonal terminal is called the pre-synaptic membrane, and the membrane of the neuron it synapses with is called the post-synaptic membrane. Penetrating the terminal from the axon are microtubules, which may transport precursor chemicals for the manufacture of neurotransmitters into the terminal. Within the terminal are mitochondria which provide the energy necessary for metabolic processes. Also there are two types of vesicles within the terminal: Storage granules, which are thought of be long-term storage containers for neurotransmitters, and Synaptic vesicles, which hold neurotransmitter for immediate release. Located on the postsynaptic membrane are specialized proteins that act as receptors for the neurotransmitter.
Myelination:
Myelination
is the process by which the support cells of the nervous system (Spongioblasts which later give rise to Glial Cells), begin to surround axons and provide them with insulation. Nerves can become functional before myelination, however it is assumed that they reach their adult level of functioning once myelination is completed. Hence, myelination provides a measure of the maturity of structures from which axons project and to which they project.
A great many peripheral nerve fibers have a myelin sheath and a Neurolemma (sheath of Schwann) outside the myelin. The myelin is actually a spiralled wrapping of several layers of cell membranes from the same Schwann Cell, which forms the Neurolemma on the outside. Each Schwann Cell contributes myelin to one segment (or internode) of a myelinated axon. Between two adjacent Schwann Cell internodes is a small gap called the Node of Ranvier. Unmyelinated fibers, however, are enfolded into the cytoplasm of a Schwann cell by a simple extension of that cell. There is no layering of Schwann cell membranes around an unmyelinated fiber.
Myelinated fibers located in the white matter of the brain and spinal cord possess a myelin sheath but have no Neurolemma because their myelin sheaths are formed by cytoplasmic extensions of Glial cells, each of which contributes myelin to several of the nearby axons.
There are actually three types of Glial Cells present in the CNS: Microglia, Oligodendrocytes, and Fibrous Astrocytes.
Microglia are phagocytic cells that form part of the nervous system's defense against infection and injury.
Oligodendrocytes, are called Satellite cells when they occur close to neural cell bodies, and Schwann cells when they occur in the Pripheral Nervous System (PNS). Oligodendrocytes form and maintain the myelin sheaths of the CNS. The cytoplasm of oligodendrocytes is characterized by rough endoplasmic reticulum but its most prominent characteristic is the enclosure of concentric layers of its own surface membrane around the axon. These concentric layers come together so closely that the oligodendrocyte cytoplasm is completely squeezed out and the original internal surfaces of the membrane become fused, presenting the ringlike appearance of the myelin sheath in cross section.
Fibrous Astrocytes; a descriptive term based on their starlike shape in the light microscope and on the fibrous nature of their cytoplasmic organelles, are less well understood. They are found mainly in regions of axons and dendrites and tend to surround or be in contact with the adventitial surface of blood vessels. Astrocytes cannot develop action potentials, they are, however, highly permeable to K+ and become depolarized if the extracellular concentration of K+ increases. Astrocytes are thought to (1) take up extracellular K+ during intense neuronal activity and to (2) buffer K+ concentration in the extracellular space. They also (3) take up and store Neurotransmitters and thus (4) store and transfer metabolites from capillaries to neurons.
Astrocytes are sensitive to a wide variety of insults to CNS tissue. Depending upon the noxious agent; they may respond with cytoplasmic swelling, accumulation of glycogen, fibrillar proliferation whitin the cytoplasm, cell multiplication, or a combination of any of these reactions. They are frequently the cells that form a permanent scar or plaque after distruction of neural elements. Functions shch as insulation (between conducting surfaces) and orginization (to surround and separate functional units of nerve endings and dendrites) have been emperically attributed to the astrocyte.
If myelination is in fact a measure of maturation, then analysis reveals that the Neocortex begins a sequential development at a relatively early age. The primary sensory areas and motor areas show some degree of myelination just before term. The secondary cortical areas become myelinated within the next four postnatal months, and by the fourth month the tertiary areas of the cortex are becoming myelinated. Even though myelination begins during the early postnatal period, it continues beyond 15 years of age and may actually increase in density as late as the sixth decade of life. Any disruption of this process can cause neural and hence behavioral, abnormalities. 
Evidence suggests very intimate contact between neuroblastic neurons and guidepost glial cells; gap junctions, for example, form transiently between the two contact cells during growth cone movement.
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