USMLE Step 1 Physiology Review 52 13 Action Potentials (1 of 2)

USMLE Step 1 Physiology Review 52 13 Action Potentials (1 of 2)

On these “Gold Standard Step 1 Facts” pages you will find Free:

  • USMLE Audio Review files from our “Gold Standard USMLE Reviews”
  • Transcriptions of those files
  • And videos (as they become available)

The idea is that you can review for the USMLE online by:

  • Listening to the Audio
  • Following along with the transcription
  • Or by watching the video (if available)

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Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3 52 13 Action Potentials (1 of 2) Below

Begin 52 13 Action Potentials (1 of 2) Transcription

Now for some questions about action potentials. 

 What are the signals used for communication throughout the nervous system and excitable tissues?

  • Action potentials.

What happens to the membrane potential during action potentials?

  • There is a rapid reversal of membrane potential.

Does the inside of the cell go negative or positive during this rapid reversal?

  • It goes positive.

 What is the time period between onset of the action potential and recovery to the resting potential in nerve and skeletal muscle cells.

  • One millisecond.

 Is this recovery time slower or faster in cardiac and smooth muscle compared to nerve and skeletal muscle cells?

  • Slower.

 What kinds of potentials initiate action potentials at sensory nerve terminals?

  • Generator potentials.

 And what kinds of potentials initiate action potentials in neurons?

  • Synaptic potentials.

 Student Doctor, please pause the tape and summarize the information discussed so far on action potentials.

  • Action potentials are the signals used for communication throughout the nervous system and excitable tissues.  There is a rapid reversal of membrane potential during action potentials.  The inside of the cell goes positive during the rapid reversal.  The time period between onset of the action potential and recovery to the resting potential in nerve and muscle cells is about one millisecond.  This recovery time is slower in cardiac and smooth muscle.  Generator potentials initiate action potentials at sensory nerve terminals.  Synaptic potentials initiate action potentials in neurons.

 And now for some more questions.

 Generator potentials and synaptic potentials are both what kind of potential? 

  • Graded potentials.

 Do these kinds of potentials propagate or are they local?

  • They are local; they do not propagate.

 Do they have a threshold? 

  • No.

 Do they have a refractory period? 

  • No.

 What is a refractory period?  Pause the tape. 

  • It is a period of time during which excitable tissue cannot become stimulated to produce a second action potential.  Its onset is associated with the action potential.

 What are the three kinds of potential that are classified as synaptic potentials?  List them from proximal to distal.

  • First, end-plate potentials.  Second, post-synaptic excitatory potentials.  Third, post-synaptic inhibitory potentials.

 Student Doctor, please pause the tape and summarize the information on action potentials discussed since the last summary.  We started with the description of generator and synaptic potentials.

  • Generator potentials and synaptic potentials are both graded potentials that are local.  They do not propagate, have no threshold, and no refractory period.  A refractory period is a period of time immediately following an action potential during which excitable tissue cannot become excitable again.  Three kinds of potentials that are classified as synaptic potentials are end-plate potentials, post-synaptic excitatory potentials, and post-synaptic inhibitory potentials.

 

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52-13 Action Potentials (1 of 2)

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