Chapter 42. Resting Membrane Potential

Learning Objectives

nervous system
the body's fast communication system, consisting of billions of neurons; divided into the peripheral and central nervous systems
potassium channels
openings in a neuron’s membrane that allow potassium ions (K+) to pass through the membrane
resting potential
the negative electrical charge inside the axon when it is in its resting state
sodium channels
openings in a neuron’s membrane that allow sodium ions to pass through the membrane
sodium-potassium pumps
special structures in a neuron’s membrane that use energy to move sodium and potassium ions through the membrane
action potential
a brief electrical charge (neural impulse) that travels down an axon
axon
part of a neuron specialized to send impulses to other neurons (or to muscles and glands)
ions
positively charged or negatively charged particles (atoms or molecules)
neural impulse
an electrical signal that carries a message along an axon
neuron
a single nerve cell, forming the basic unit of the nervous system
Resting Membrane Potential
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Learning Objective:

Describe the factors that produce the neuron’s resting membrane potential.

Understand the importance of the resting membrane potential in neural communication.

Review

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1. Within the nervous system, information travels along an individual neuron in the form of a brief neural impulse, called an action potential. In order for the action potential to be recognized as a signal or message, it must stand out from the “background” state of the neuron’s axon, called the resting potential.

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2. A membrane potential is the difference in electrical charge between the inside and outside of the neuron’s membrane. In its resting state, the interior of the axon is electrically negative when compared to the outside. Typically, the resting potential is measured at about -70 millivolts.

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3. The axon’s interior fluid is electrically negative because it contains many large negatively charged protein molecules, along with much smaller positively charged potassium ions (K+). The fluid outside the axon contains many positively charged sodium ions (Na+). Active sodium-potassium pumps maintain the different concentrations of sodium and potassium ions.

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4. The positively charged sodium ions outside the axon are strongly attracted to the negative axon interior. Because the sodium channels are closed, and most of the potassium channels are closed in the axon’s resting state, it’s not possible for those ions to move across the membrane.

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5. When the neuron fires (generates an action potential), the sodium channels open, allowing sodium ions to rush in and disturb the resting potential. Because the sodium ions have a positive charge, the interior of the axon becomes electrically positive. This positive surge (up to about +40 millivolts) lasts only for a brief period until the potassium channels open and potassium ions flow out of the axon, returning the axon interior to its resting (negative) state.

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6. The sodium-potassium pumps complete the process by restoring the appropriate concentrations of sodium and potassium ions inside and outside the axon.

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Practice: Exploring the Resting Potential

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Practice: Exploring the Resting Potential

Roll over each of the labels to see a description of the role that component plays in maintaining the resting membrane potential and allowing researchers to study it.

K+
Na+
K+ channel
Na+ /K+ pump
Na+ channel
Outside the axon
Inside the axon
Protein
Voltmeter
Role in maintaining or measuring the resting potential:

potassium ions have a positive charge; concentrated inside the axon

sodium ions have a positive charge; concentrated outside the axon

closed to limit movement of potassium ions out of axon

maintains concentration of sodium and potassium ions

closed to prevent movement of sodium ions into axon

exterior of the axon is electrically positive

interior of the axon is electrically negative

large negatively charged molecules keep interior or axon negative

measures the electrical difference between the two electrodes

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Quiz 1

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Quiz 1

The situations above refer to the small section of the axon shown within the rectangle. Drag each voltmeter reading to the gray area next to the appropriate situation. When all the voltmeters have been placed, select the CHECK ANSWER button.

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Perhaps you should go back to review the way that the resting membrane potential is created and maintained.
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−70 mV
+40 mV
−20 mV

membrane potential when the axon is in its resting state

membrane potential after the sodium channels have opened and the maximum number of sodium ions have rushed into the axon

membrane potential after the sodium channels have closed, the potassium channels have opened, and potassium ions are flowing rapidly out of the axon

Quiz 2

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Quiz 2

Match the terms to their descriptions by dragging each colored circle to the appropriate gray circle. When all the circles have been placed, select the CHECK ANSWER button.

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Perhaps you should go back to review the key terms related to the resting membrane potential.
action potential
sodium ions
potassium ions
resting potential
sodium-potassium pumps
positively charged particles that flow into the axon, disrupting the resting potential
molecules that use energy to move ions through the axon membrane
a brief positive electrical charge that travels down an axon, disrupting the resting potential
positively charged particles that flow out of the axon, restoring the resting potential
the negative electrical charge inside the axon when the neuron is not firing

Conclusion

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