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Guy Proulx (13)

4. The Structure and Electrical Activity of Neurons.docx

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PSYC 3530
Guy Proulx

4. The Structure and Electrical Activity of Neurons Sunday, September 15, 2013 5:57 PM The Neuron's Structure  Epilepsy-- a disease in which discharges of abnormal electrical activity in the brain interfere with normal movements, thought, and consciousness  The dendrites’ surface area is further increased by many branches and by many small protrusions called dendritic spines that cover each branch o A neuron may have from 1 to 20 dendrites, each of which may have one or many branches, and the spines on the branches may number in the many thousands  Each neuron has a single axon, extending out of an expansion of the cell body known as the axon hillock  The axon may have branches called axon collaterals, which usually emerge from it at right angles  Toward its end, the axon may divide into a number of smaller branches called teleodendria  At the end of each teleodendrion is a knob called a terminal button  The terminal button sits very close to a dendritic spine on another neuron, although it does not touch that spine. This “almost connection,” consisting of the surface of the axon’s end foot, the corresponding surface of the neighboring dendritic spine, and the space between the two, is the synapse    The cell is a miniature factory, with departments that cooperate to make, ship, and export proteins, the cell’s products  A cell’s outer cell membrane separates it from its surroundings and allows it to regulate the materials that enter and leave its domain      Prominent among the cell’s internal membranes is the nuclear membrane that surrounds the cell’s nucleus  The nucleus, like the executive office of a factory, houses the blueprints— genes and chromosomes—where the cell’s proteins are stored and copied  The endoplasmic reticulum, an extension of the nuclear membrane, is where the cell’s protein products are assembled in accordance with the genes’ instructions  Neurons and glia are tightly packed together in the brain, but, like all cells, they are separated and cushioned by extracellular fluid  This intracellular fluid, or cytoplasm, also is made up mainly of water with dissolved salts and other chemicals, but the concentrations of dissolved substances inside and outside the cell are very different  The membrane bilayer is composed of a special kind of molecule called a phospholipid o  Charged particles are collectively called ions  The blueprints for proteins are embedded in the chemical structure of giant molecular complexes in the nucleus called chromosomes  A gene is a segment of a DNA strand that encodes the synthesis of a particular type of protein molecule  Much as a sequence of letters spells out a word, the sequence of nucleotide bases “spells out” the order in which amino acids, the building blocks of proteins, should be assembled to construct a certain kind of protein  DNA --> mRNA --> protein   Proteins destined to be excreted, a process called exocytosis, remain within their membranes, which fuse with the cell membrane, allowing the protein to be expelled into the extracellular fluid, perhaps as a neurotransmitter carrying a message to another neuron  Transmembrane proteins o The Neuron’s Electrical Activity  Oscilloscope-- an instrument that turns electrical fluctuations into visible signals  Voltage-- strength of the charged electrical current  Three factors influence the movement of ions into and out of cells: o 1) A concentration gradient  Requiring no work, diffusion results from the random motion of molecules as they jostle and bounce about, gradually dispersing throughout the solutio
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