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Chapter2Transparencies - Chapter2: INEURONanervecell;...

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Chapter 2: NEUROSCIENCE AND BEAHVIOR I – NEURON - a nerve cell; the basic building block of the nervous system Everything Psychological is Simultaneously Biological Dendrite : Branching extensions of a neuron that receive impulses from other neurons or  from sensory organs and conduct them toward the cell body. Axon : Extension of a neuron, ending in branching terminal fibers through which messages  pass to other neurons or to muscles or glands. Myelin sheath : Layer of fatty tissue surrounding fibers of many neurons; insulates and  increases the speed of transmission of neural impulses; impulse hops from one  node/segment to the next; speed of transmission varies from 2 mph to 200 mph;  measured in milliseconds (1000 th  of a second) vs. computers (nanoseconds – 1 billionth of  a second). Action potential : A neural impulse; a brief electrical charge that travels down an axon;  generated by the movement of positively charged atoms in and out of channels in the  axon’s membrane; triggers by stimulation for sensory organs or other neurons. Resting potential: Neuron has more negatively charged ions inside (selective  permeability); when the neuron fires, positively charged ions and the impulse  spreads down the neuron (depolarization); during the refractory period, neuron  pumps the positively charged ions back out.   Threshold: Minimal level of stimulation required to trigger a neural impulse;  excitatory impulses must exceed inhibitory impulses and achieve threshold for the  neuron to fire. Action potential (AP) is all-or-none – either the neuron fires or not (stronger  stimulation does not affect strength or speed of the AP).  However, stronger  stimulation triggers more frequent firing and more neurons firing. II – HOW NEURONS COMMUNICATE AND INFLUENCE BEHAVIOR Synapse : junction between the axon tip of the sending neuron and the dendrite or cell  body of the receiving neuron. The tiny gap at this junction is called the synaptic gap or  cleft. Neurotransmitters : Chemical messengers that traverse the synaptic gaps from the sending  neuron and bind to receptor sites on the receiving neuron, influencing whether that  neuron will generate a neural impulse. Overall : Most neurons have a resting rate of random firing, which either increases or  decreases with input from other neurons and from chemicals that affect their sensitivity. If  the neuron receives more excitatory than inhibitory messages, it fires often. More  electrical impulses flash down its axon, releasing more packets of neurotransmitters,  which diffuse across their synaptic gaps to other neurons.
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