USMLE Step 1 Physiology Review 54 05 Smooth Muscle (3_3)

USMLE Step 1 Physiology Review 54 05 Smooth Muscle (3_3)

 

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 54 05 Smooth Muscle (3_3) Below

Begin 54 05 Smooth Muscle (3_3) Transcription

Okay, now for some more questions.

What happens to myosin when calcium concentration dips to intermediate levels?

  • The myosin is dephosphorylated.

What enzyme dephosphorylates myosin?

  • Myosin light chain phosphatase, abbreviated as MLCP.

What are the two enzymes that control smooth muscle contractile activity?

  • Myosin light chain kinase and Myosin light chain phosphatase.

At intermediate levels of calcium concentration the cross bridges between actin and dephosphorylated myosin may remain attached. What is the term of this state of lingering cross bridge attachment?

  •  Latch state.

Why is the latch state important for muscle tissues in structures like blood vessels and sphincters?

  • So that muscle tissues in structures like blood vessels and sphincters can maintain active tone.

When does relaxation occur?

  • When cytosolic calcium concentration declines to resting levels.

What happens to the calcium that was in the cytosol?

  • It is extruded into the extra cellular space and/or taken up by the sarcoplasmic reticulum.

Student Doctor, please pause the tape and summarize the information about contraction of smooth muscle discussed since the last summary. The first question was about the dephosphorylation of myosin.

  • When calcium concentration dips down to intermediate the levels the myosin is dephosphorylated by myosin light chain phosphatase, abbreviated as MLCP. Myosin light chain kinase and myosin light chain phosphatase are the two enzymes that control smooth muscle contractile activity. At intermediate levels of calcium concentration the cross bridges between actin and dephosphorylated myosin may remain attached. The term for this state of lingering cross bridge attachment is latch state. The latch state is important for muscle tissues in structures like blood vessels and sphincters so that these muscle tissues can maintain active tone. Relaxation occurs when cytosolic calcium concentration declines to resting levels. The calcium that was in the cytosol is extruded into the extra cellular space and/or taken up by the sarcoplasmic reticulum.

 

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54-03 Smooth Muscle

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