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BIO 140 Human Biology I - Questions and Solutions

The Action Potential - Solutions

Review Questions

1. What ion enters a neuron causing depolarization of the cell membrane?

  1. sodium
  2. chloride
  3. potassium
  4. phosphate

2. Voltage-gated Na+ channels open upon reaching what state?

  1. resting potential
  2. threshold
  3. repolarization
  4. overshoot

3. What does a ligand-gated channel require in order to open?

  1. increase in concentration of Na+ ions
  2. binding of a neurotransmitter
  3. increase in concentration of K+ ions
  4. depolarization of the membrane

4. What does a mechanically gated channel respond to?

  1. physical stimulus
  2. chemical stimulus
  3. increase in resistance
  4. decrease in resistance

5. Which of the following voltages would most likely be measured during the relative refractory period?

  1. +30 mV
  2. 0 mV
  3. -45 mV
  4. -80 mv

6. Which of the following is probably going to propagate an action potential fastest?

  1. a thin, unmyelinated axon
  2. a thin, myelinated axon
  3. a thick, unmyelinated axon
  4. a thick, myelinated axon


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Critical Thinking Questions

1. What does it mean for an action potential to be an “all or none” event?

Solution: The cell membrane must reach threshold before voltage-gated Na+ channels open. If threshold is not reached, those channels do not open, and the depolarizing phase of the action potential does not occur, the cell membrane will just go back to its resting state.

2. The conscious perception of pain is often delayed because of the time it takes for the sensations to reach the cerebral cortex. Why would this be the case based on propagation of the axon potential?

Solution: Axons of pain sensing sensory neurons are thin and unmyelinated so that it takes longer for that sensation to reach the brain than other sensations.


Click here to return to Chapter 34

OpenStax, The Action Potential. OpenStax CNX. Nov 7, 2014 http://cnx.org/contents/401af334-2930-4731-ba9a-14a346326e63@5. © Nov 7, 2014 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License 4.0 license.