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Chapter 3

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Simon Fraser University
PSYC 100
A.George Alder

Chapter 3 10/2/2012 8:35:00 AM Neurons; specialized (nerve) cells that act as the basic building blocks of the nervous system and mainly used to send messages back and forth  Do two important things o Generate electricity that creates nerve pulses o Release chemicals that allow them to communicate with other neurons and with muscles and glands  Three main parts; o Cell Body; aka soma, contains the biochemical structures needed to keep the neuron alive  Nucleus carries the genetic information that determines how the cell develops and functions  Combines and processes information from the dendrites  Has receptor areas that can be directly simulated b other neurons o Dendrites; branchlike fibers that act as specialized receiving units  collect messages from neighbouring neurons and send them on to the cell body o Axon; conducts electrical pulses away from the cell body to other neurons, muscles, or glans  Branches out at its end to form a number of axon terminals  Each axon may connect with dendritic branches from numerous neurons, making it possible for a single neuron to pass messages to as many as 50,000 other neurons Structural elements of a typical neuron. Stimulation received by the dendrites or soma (cell body) may trigger a nerve impulse, which travels down the axon to stimulate other neurons, muscles, or glands. Some axons have a fatty myelin sheath interrupted at intervals by the nodes of Ranvier. The myelin sheath helps to increase the speed of nerve conduction.  Glial Cells; manufacture nutrient chemicals that neurons need, form the myelin sheath around some axons, and absorb toxins and waste matierials that might damage neurons o Modulating the communication among other neurons o protect the brain from toxins  During prenatal brain development, as new neurons are being formed through cell division, glial cells send out long fibres that guide newly divided neurons to their targeted place in the brain  glial cells outnumber neurons about ten to one.  Blood Brain barrier; prevents many substances (incl. toxins) from entering the brain o Walls of the blood vessels in the brain contain smaller gaps than anywhere else in the body (more concentrated?) & also covered by a specialized type of glial cell Electrical Activity of Neurons Let's first consider how nerve impulses occur. Nerve activation involves three basic steps:  At rest, the neuron has an electrical resting potential due to the distribution of positively and negatively charged chemicals (ions) inside and outside the neuron.  When stimulated, a flow of ions in and out through the cell membrane reverses the electrical charge of the resting potential, producing an action potential, or nerve impulse.  The original distribution of ions is restored, and the neuron is again at rest Ion Channel; a passageway or channel in the membrane that can open to allow ions to pass through  Filters out certain substances by having them follow through alternative ion passages What causes the negative resting potential of neurons? When is a neuron said to be in a state of polarization? 
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