Transcript What is the neuron`s resting potential?

Psychology 304:
Brain and Behaviour
Lecture 11
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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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By the end of today’s class, you should be able to:
1. describe the neurological basis of multiple sclerosis.
2. explain how the resting potential of a neuron is
maintained.
3. distinguish between EPSPs, IPSPs, and action
potentials.
4. describe the electrochemical changes that trigger an
action potential.
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From last class …..
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Structure of Astrocytes
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What are glial cells? (continued)
• Glial cells have been implicated in multiple sclerosis:
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Multiple Sclerosis
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What is the neuron’s resting potential?
• A neuron’s membrane potential refers to the
difference in electrical charge between the inside and
the outside of the cell.
• 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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The 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 neurotransmitters 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 hyperpolarize 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 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?
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