Smooth Muscles: Contraction and Relaxation

by Thad Wilson, PhD

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    So let’s go through the full process of how calcium causes the muscle to contract. And to give you a little compare and contrast, we’ll use skeletal muscle as our contrasting agent. So you start off with calcium, you end up with a contraction. So let’s go through this process. Smooth muscle, calcium binds to calmodulin, which then activates myosin light chain kinase, which phosphorylates myosin, which then causes actin-myosin interaction, crossbridge cycling, and contraction. In skeletal muscle, calcium binds to troponin, which moves tropomyosin off the active site on actin. Once actin is available, myosin-actin interactions occur, crossbridge cycling happens, and you get a contraction. So those are the overall pathways between striated muscle contraction and smooth muscle contraction. Now, let’s break each one of these parts down. So, once we have calcium available, if we are in smooth muscle, we’re binding to calmodulin. In skeletal muscle, striated muscle, we’re using troponin. So both of these are the calcium-binding proteins, but they are different depending upon which tissue we’re talking about. Their activation also activates a different molecule. In terms of striated muscle, troponin moves tropomyosin off of an active site. In terms of smooth muscle, calmodulin activates myosin light chain kinase. The interesting thing about these two differences is myosin light chain kinase is known as thick filament regulation, while the movement of troponin is thin filament regulation. So what is the think filament? That’s myosin. What’s the thin filament? Actin. In terms of smooth muscle, you get myosin light chain kinase to phosphorylate something, and in terms of skeletal muscle, you get tropomyosin to move off of a binding site. So now let’s talk about the actin-myosin interactions. So myosin is what is being regulated on smooth muscle, actin is what’s being regulated in skeletal muscle. Both...

    About the Lecture

    The lecture Smooth Muscles: Contraction and Relaxation by Thad Wilson, PhD is from the course Musculoskeletal Physiology.

    Included Quiz Questions

    1. Calmodulin
    2. Myosin phosphatase
    3. Actin
    4. Rho kinase
    1. Store-operated channels
    2. SERCA
    3. Na-Ca exchangers
    4. Na-K ATPase

    Author of lecture Smooth Muscles: Contraction and Relaxation

     Thad Wilson, PhD

    Thad Wilson, PhD

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