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Chapter 3 Notes.docx

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Psychology 1000

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Chapter 3: Biological Foundations of Behaviour - A spike was propelled through the face and head of Phineas Gage - His physical health was good, and he recovered - The equilibrium between his intellectual faculties and animal propensities had been destroyed. - People said he was ‘no longer Gage’ The Neural Bases of Behaviour Neurons: - Specialized nerve cells that are linked together in circuits - At birth, brain contains 100 billion - Has 3 main parts o Cell body – soma contains biochemical structures to keep neuron alive and its nucleus carries genetic info that determines cell development and function o Dendrites – emerge from cell body, branch-like fibres, receiving units that collect info from other neurons o Axon – extends from cell body, conducts electrical impulses away from cell body to other neurons, muscles, or glands - Supported by Glial cells – surround neurons and hold them in place, make nutrient chemicals, form the myelin sheath around some axons, and absorb toxins & waste materials - Blood-brain barrier – prevents many substances and toxins from entering the brain Nerve Conduction: An Electrochemical Process - Neurons: generate electricity and release chemicals, surrounded by cell membrane, surrounded by a salty liquid environment (positively charged) inside is negatively charged - Resting potential - -70mV (polarized) Action Potential: - Action Potential: nerve impulse – a sudden reversal in the neuron’s membrane voltage (moves from -70mV to +40mV) - Shifting from negative to positive = depolarization - When dendrites or cell body of a neuron are stimulated by axons from other neurons, small shifs occur in cell membrane’s electrical potential - Graded potentials: proportional to the amount of incoming stimulation ( not strong: partially depolarized, but not enough to generate action potential) - Action potential Threshold: if graded potential is large enough – neuron discharged with an action potential - All-or-none law – either occurs with maximum intensity or does not occur at all - ion channels – allows specific ions to cross the cell membrane and enter or leave the cell o this creates a state of partial depolarization - The action potential threshold is -55mV (+15mV decrease from resting) - In order to restore resting polarity, K channels open and the positively charged potassium ions leave the cell - Immediately after an impulse passes along the axon, there occurs a refractory period – time period when the membrane is not excitable and cannot discharge another action potential The Myelin Sheath - Interrupted at regular intervals by the nodes of Ranvier where the myelin is either thin or absent - Unmyelinated axons: action potential travels down the axon length like a burning fuse - Myelinated axons: electrical conduction can skip from node to node (high conduction speeds) - Increased efficiency of neural transmission that results is partly responsible for the gains that infants exhibit in muscular coordination as they grow older - Multiple Sclerosis: occurs when the person’s own immune system attacks the myelin sheath o Disrupts delicate timing of nerve impulse
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