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Chapter 3

Chapter 3

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Department
Psychology
Course
Psychology 1000
Professor
Terry Biggs
Semester
Fall

Description
Psychology 1000 Chapter 3 Notes CHAPTER 3 Biological Foundations of Behaviour Neurons Neurons: nerve cells that constitute the basic building blocks of the nervous system 3 main parts of neuron: o a cell body (soma) to keep neuron alive, nucleus carries genetic information that determines how the cell develops and functions o dendrites collect messages from neighbouring neurons and send them on to the cell body o axon Conducts electrical impulses away from the cell body to other neurons, muscles or glands Branches out on ends to make axon terminals Each axon may connect with dendritic branches making it possible for a single neuron to pass messages to as many as 50,000 other neurons Glial cells: o surround neuron and hold them in place o Manufacture nutrient chemicals that neurons need, o they form myelin sheath around some axons o absorb toxins and waste materials that may damage neurons o Blood-brain Barrier: prevents many substances from entering the brain Nerve Conduction: An Electrochemical Process Neurons do 2 important things: 1 Psychology 1000 Chapter 3 Notes o Generate electricity o Release chemicals Neurons surrounded by positively charged sodium ions Inside it contains some positively charged potassium ions but also contains negative ions Inside of neuron is electrically negative in relation to the outside producing an electrical resting potential o Polarized: neuron in resting state The Action Potential Action Potential: sudden reversal in neurons membrane voltage, in which the voltage moves from -70 millivolts to +40 millivolts o Depolarization: shift from negative to positive voltage Graded Potentials: dendrites or the cell body of a neuron are stimulated by axons from other neurons and small shifts occur in the cell membranes electrical potential Action Potential Threshold: intensity of stimulation needed to produce an action potential Action potential obeys the all or none law o All or None Law: either occurs with maximum intensity or doesnt occur at all Ion Channels: special protein molecules located on the membrane of a neuron that control the entry and exit of specific ions o Creates a state of partial depolarization that may reach the action potential threshold Complete Depolarization o When a neuron is at its resting potential, positively charged sodium ions are kept inside the cell o When the membrane reaches its threshold for generating an action potential, specifc ion channels are activated 2 Psychology 1000 Chapter 3 Notes o Sodium ion channels are usually closed but when the membrane reaches the threshold for generating an action potential, the sodium ion channels open and positively charged sodium ions flow into the neuron attracted by the negative electrical force within the cell o Positively charged sodium ions carry positive electrical charge into the interior of the cell o Interior of the neuron goes from being negative to being more positive than the outside of the cell o Sodium ion channels dont stay open very long o In order to restore resting polarity, potassium channels open and the positively charged potassium ions leave the cell o Action potential started chain reaction wave that flows along membrane as succeeding sodium channels open and the process is repeated o After action potential, sodium ions trapped inside are pumped outside o Potassium ions that left during the action potential are pumped back inside the neuron o After an impulse passes any given point along the axon, a refractory period occurs Refractory Period: period during which the membrane is not excitable and cannot discharge another action potential o Limits the rate at which action potentials can be triggered in a neuron o Strong stimulus may increase the rate of firing of the individual neuron or it may increase the number of neurons that fire The Myelin Sheath Axons are covered by a tubelike myelin sheath o Myelin Sheath: fatty, whitish insulation layer derived from glial cells during development and increases speed of neural transmission In unmyelinated axons, action potential travels down the axon length 3 Psychology 1000 Chapter 3 Notes o Electrical conduction can skip from node to node and these great leaps from one gao to another account for high conduction speed Multiple selerosis is caused from damages to the myelin coating o Disrupts timing of nerve impulses, resulting in jerky, uncoordinated movements and paralysis How Neurons Communicate: Synaptic Transmission Santiago Ramon y Cajal and Charles Sherrington argued that neurons communicated in a synapse o Synapse: functional (not physical) connection between a neuron and its target Otto Loewi demonstrated that neurons released chemicals and these chemicals carried the message from neuron to the next cell in the circuit Synaptic cleft is between the axon terminal of one neuron and the dendrite of the next neuron o Synaptic Cleft: tiny gap or space Neurotransmitters Neurotransmitters: chemical substances that carry messages across the synapse to either excite other neurons or inhibit their firing Chemical communication involves 5 steps: 1. Synthesis Chemical molecules are formed inside the neuron 2. Storage When Molecules stored in synaptic vesicles within the axon terminals Synaptic Vesicles: chamber 4
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