Chapter 7. Action Potentials

Learning Objective

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)
axon terminals
branching fibers at the end of an axon that contain the neurotransmitters; also called synaptic terminals or terminal buttons
cell body
part of a neuron that contains the genetic material (in the nucleus) and generates energy; also called the soma
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
potassium channels
openings in a neuron’s membrane that allow potassium ions (K+) to pass through the membrane
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 Potentials
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Learning Objective:

Describe the sequence of events within the neuron that produces an action potential.

Review

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The figure includes an image of a cell with a cell body on the left side of the screen. Extending from the cell body is a tube labeled as “axon”. The axon branches into many smaller tubes, which end with axon terminals. The cell has many dendrites extending from the cell body as well, which look like branches. A picture of a sun is in the middle of the axon to represent the neural impulse going down the axon away from the cell body.

1. When a neuron is stimulated, it "fires," sending a neural impulse down its axon from the cell body to the axon terminals.

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The figure is a cross-section of an axon. The axon has been cut vertically to reveal the inside of the axon. Outside and inside the axon are positive sodium and potassium ions. Some sodium ions are shown entering the axon, while some potassium ions are shown leaving the axon. There are more sodium ions than potassium ions within the axon, and more potassium than sodium ions outside the axon. The cell is generating an action potential.

2. The neural impulse is actually a brief electrical charge called an action potential. Action potentials are generated by the movement of positively charged ions in and out of the axon.

Review

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The figure is a cross-section of an axon. The axon has been cut vertically to reveal the inside of the axon. Positive sodium ions are shown entering the gates on the walls of the axon, making the inside of the cell more positive in that area and creating an action potential.

3. In its resting state, the interior of the axon is electrically negative. As the action potential travels down the axon, each tiny section of the axon opens its sodium channels, allowing positively charged sodium ions to flow into the axon. For a brief moment, that section of the axon becomes electrically positive.

Review

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The figure is a cross-section of an axon. The axon has been cut vertically to reveal the inside of the axon. Positive sodium ions are shown entering the gates on the walls of the axon, making the inside of the cell more positive in that area and creating an action potential. Once the action potential is generated and moves down the axon, the gates on the walls of the axon pump potassium out of the axon.

4. Soon, potassium channels open, and then the positive charge decreases as positive potassium ions flow out of the axon.

Review

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Review

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The figure is a cross-section of an axon. The axon has been cut vertically to reveal the inside of the axon. Positive sodium ions are shown entering the gates on the walls of the axon, making the inside of the cell more positive in that area and creating an action potential. Once the action potential is generated and moves down the axon, the gates on the walls of the axon pump potassium out of the axon. The axon then returns to its original resting state.

5. As the action potential moves further down the axon, the original section of the axon returns to its resting state, as special sodium-potassium pumps restore the original concentrations of sodium and potassium ions.

Practice 1: Generating an Action Potential

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Practice 1: Generating an Action Potential

Play the animation to watch the sequence of events in an action potential.

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Practice 2: Measuring the Action Potential

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Practice 2: Measuring the Action Potential

Select the PLAY button to measure the electrical charge before and after the action potential.

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Researchers can use a tiny electrode (connected to a voltmeter) to measure the electrical charge at a particular axon location.

Researchers then stimulate the axon to produce an action potential. Note the change in the axon’s electrical charge as the action potential sweeps past that location on the axon.

Quiz 1

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Quiz 1

Drag each description to the appropriate gray area to form the correct sequence of events that occurs when an action potential is generated. When all the descriptions have been placed, select the CHECK ANSWER button.

Select the NEXT button and move to Quiz 2.
Perhaps you should go back to review events related to action potentials.
Potassium channels open.
Sodium channels open.
Sodium ions flow into the axon, making the interior positive.
Potassium ions flow out of the axon, making the interior negative.
Sodium-potassium pumps restore the proper ion ratios.
The axon is in its resting state. The interior is negative.

Quiz 2

matching_test

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.

Select the NEXT button and move to the Conclusion.
Perhaps you should go back to review events related to action potentials.
action potentials
sodium channels
potassium channels
sodium-potassium pumps
allow ions to flow into the axon
restore proper ion concentrations
neural impulses that move down axon
allow ions to flow out of the axon

Conclusion

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