Describe the factors that produce the neuron’s resting membrane potential.
Understand the importance of the resting membrane potential in neural communication.
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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.
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.
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
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.
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.