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psych midterm notes.docx

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Wilfrid Laurier University
Don Morgenson

Chapter 3 The Biological Bases of BehaviourNervous System The Basic Hardware Nervous system is living tissue composed of cells which fall into two major categories neurons and gliaNeurons individual cells in the nervous system that receive integrate and transmit information Soma or cell body contains the nucleus and much of the chemical machinery common to most cells Rest of the neuron is dedicated to handling information Neurons have a number of branched feelerlike structures called dendritic trees Each branch is a dendrite parts of the neuron that is specialized to receive information From dendrites information flows from the cell body and travels away from the soma along the axon a long thin fibre that transmits signals away from the soma to other neurons or to muscles or glands Axons are wrapped in cells with a high concentration of white fatty substance called myelinMyelin sheath insulating material derived from glial cells that encases some axonso Speeds up the transmission of signals that move along axons Axon ends in a cluster of terminal buttons small knobs that secrete chemicals called neurotransmitterso These chemicals serve as messengers that may activate neighbouring neurons The points at which the neurons interconnect are called synapses junctions where information is transmitted from one neuron to anotherSUMMARYInformation received at dendrites passed through the soma along the axon transmitted to the dendrites of other cells at synapsesGlia cells found throughout the nervous system that provide various types of support for Neurons Are smaller than neurons but outnumber them by about 10 to 1 Account for over 50 of the brains volume Supply nourishment to neurons help remove neurons waste products and provide insulation around many axonsThe Neuron at Rest A Tiny Battery Neural impulse is an electrochemical reactionInside and outside the neuron are fluids containing electrically charged atoms and molecules called ions Cell membrane semipermeablepermits movement of some ionso Positively charged sodium and potassium ions and negatively charged chloride ions move back and forth across cell membrane at different rateso Different flow rateshigher concentration of negatively charged ions inside the cell Resting potential its stable negative charge when the cell is inactiveThe Action Potential When neuron is stimulated channels in its membrane open allowing positively charged sodium ions to rush ino For an instant the neuron charge is less negative or positive creating an action potential a very brief shirt in a neurons electrical charge that travels along an axon After the firing of an action potential the channels in the cell membrane that opened to let in sodium close up and some time is needed before they are ready to open again and the neuron can fire Absolute refractory period the minimum length of time after an action potential during which another action potential cannot begin Followed by brief relative refractory period where the neuron can fire but its threshold for firing is elevated so more intense stimulation is required to initiate an action potentialThe AllorNone Law Neurons firing action potential is an allornone proposition Various neurons transmit neural impulses at different speedsThe Synapse Where Neurons MeetSending Signals Chemicals as Couriers Synaptic cleft microscopic gap between the terminal button of one neuron and the cell membrane of another neuron Signals have to cross this gap to permit neurons to communicatepresynaptic neuron sends signal across gap and postsynaptic neuron receives it Arrival of an action potential at axons terminal buttons triggers the release of neurotransmitters chemicals that transmit information from one neuron to another Most chemicals stored in small sacs called synaptic vesicles Neurotransmitters are released when a vesicle fuses with the membrane of the presynaptic cell and its contents spill into the synaptic cleft After release neurotransmitters diffuse across the synaptic cleft to the membrane of the receiving cell
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