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Chapter2Transparencies - Chapter 2 NEUROSCIENCE AND...

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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. 1
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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. Major Neurotransmitters and their Functions Acetylcholine (ACh): Enables muscle action, learning, and memory Deficiency implicated in Alzheimer’s disease. Dopamine : Influences movement, learning, attention, and emotion Excess dopamine receptor activity linked to schizophrenia; starved of dopamine, the brain produces the tremors and decreased mobility of Parkinson’s disease.
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