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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.

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?