Muscle Contractions

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Muscle Physiology
Sliding-Filament Theory
thick filaments (myosin) move past thin filaments (actin)
sarcomeres shorten while filaments remain same length
requires actin-myosin binding sites, ATP and  Ca2+


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Role of Ca2+ in muscle contraction 
allows for myosin binding on actin, by shifting the troponin-tropomyosin complex



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The actin-myosin ATP cycle
The myosin head is ready to bind actin once it has hydrolyzed ATP
Pi is released (now, strong bond between actin and myosin is able to form - this is called a cross-bridge)
Power stroke happens
ADP is released
Now, muscle is in contracted state
ATP binds myosin again, causing release of actin ––> back to the relaxed state
no ATP available? No relaxation. This is what happens during rigor mortis.
Wize Tip
This cycle will continue as long as Ca+ and ATP are available

What is true about muscle contractions after death?

stiffening of the body because there is no Ca+ release from the sarcoplasmic reticulum

stiffening of the body because there is no more ATP being made to break the cross bridges

stiffening of the body because of troponin breakdown

stiffening of the body because Ca+ is not taken back into the sarcoplasmic reticulum

I don't know

If an AP from an alpha motor neuron does not reach the muscle, what will happen to the actin-myosin-ATP cycle?

the myosin will not be able to release actin because no ATP is present

ATP cannot energize the myosin head

Ca++ will not leave the sarcoplasmic reticulum and the muscle fiber will remain in a relaxed state

no power stroke will happen because actin and myosin are bound, but have no ATP available.

I don't know

Wize University Physiology Textbook > Skeletal Muscle Physiology

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