1 Psychology 304: Brain and Behaviour Lecture 11.
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Transcript of 1 Psychology 304: Brain and Behaviour Lecture 11.
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Psychology 304: Brain and Behaviour
Lecture 11
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From a classmate ....
An amusing YouTube clip regarding brain structures:
http://www.youtube.com/watch?v=fh5hjbQWQ78&feature=related
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The Cells of the Nervous System and The Generation of Electrochemical Neural Signals
1. What are glial cells? (continued)
2. What is the neuron’s resting potential?
3. What causes a neuron to produce an action potential?
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2. explain how the resting potential of a neuron is maintained.
By the end of today’s class, you should be able to:
3. distinguish between EPSPs, IPSPs and action potentials.
1. discuss glial-mediated neural regeneration.
4. describe the electrochemical changes that trigger an action potential.
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What are glial cells? (continued)
• Oligodendrocytes do not facilitate neural regeneration.
• Schwann cells do facilitate neural regeneration.
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Myelination of Axons in the CNS by Oligodendrocytes vs. Myelination of Axons in the
PNS by Schwann Cells
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• A neuron’s membrane potential refers to the difference in electrical charge between the inside and
the outside of the cell.
What is the neuron’s resting potential?
• The membrane potential of a resting neuron is about -70 mV (-50 to -80 mV). Thus, the resting neuron is “polarized.”
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• Resting neurons are polarized due to the distribution of ions around the neuron’s membrane.
• Sodium ions (Na+), potassium ions (K+), chloride ions (Cl-) and negatively charged protein ions are distributed
unevenly across the neuron’s membrane.
• The ratio of negative to positive charges is greater inside the resting neuron than outside.
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9The Resting Neuron
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• Two processes maintain the unequal distribution of ions across the membrane of resting neurons:
1. The differential permeability of the membrane to ions (most permeable to K+ and Cl-; least permeable to negatively charged protein ions).
2. The action of sodium-potassium pumps (continually exchange three Na+ ions inside the neuron for two K+ ions outside of the neuron).
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A Sodium-Potassium Pump in a Neuron Membrane
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What causes a neuron to produce an action potential?
• A neuron produces an action potential or “fires” when it generates and conducts an electrochemical signal.
• A neuron receives electrochemical signals from thousands of adjacent neurons, in the form of “synapses” onto the dendrites or cell body of the target neuron.
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Electron Micrograph of Synaptic Contact
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• The terminal buttons release chemicals or neuro-transmitters that bind to receptors on the dendrites or cell body of the target neuron.
• The neurotransmitters can excite or inhibit the target neuron.
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• Neurotransmitters that excite the target neuron depolarize its membrane, producing excitatory postsynaptic potentials (EPSPs). EPSPs increase the likelihood that the target neuron will fire.
• Neurotransmitters that inhibit the target neuron hyper-polarize its membrane, producing inhibitory postsynaptic potentials (IPSPs). IPSPs reduce the likelihood that the target neuron will fire.
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• The EPSPs and IPSPs are conducted to an area adjacent to the axon hillock and integrated.
• If the integrated sum of the EPSPs and IPSPs is sufficient to depolarize the membrane to the threshold of activation (-40 to -65mV), an action potential is generated.
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Neural Integration
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• An action potential is a momentary reversal of the membrane potential from a highly negative value (e.g.,
-70mV) to a highly positive value (e.g., +50 mV).
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The Cells of the Nervous System and The Generation of Electrochemical Neural Signals
1. What are glial cells? (continued)
2. What is the neuron’s resting potential?
3. What causes a neuron to produce an action potential?