Module 1 - Baseline Body Systems - Skeletal Muscle
Is skeletal muscle striated or non-striated?
Is skeletal muscle under voluntary or involuntary control?
What nervous system regulates skeletal muscle?
The somatic nervous system
What are the repeating units in skeletal muscle called?
What are thick filaments made up of?
Thousands and thousands of myosin molecules
What are thin filaments made up of?
Actin molecules, troponin molecules and tropomyosin molecules
Describe cross bridge cycling
1. Globular heads stick out at a 90° angle from the thick filaments but do not actually make contact with the thin filament. To make that contact they have to be activated which requires energy; an enzyme is present within the globular heads which is able to split ATP into ADP and Pi. An ATP molecule therefore binds with the myosin, it is split into ADP and Pi and bound to the myosin head making it an activated myosin molecule.
2. The activated myosin molecules make use of actin binding sites within the globular heads and form cross bridges with the actin molecules in the thin filaments.
3. Forming a cross bridge causes a conformational change in the head of the myosin molecule (cross bridge formation causes a release in the stored ADP which bends the head of the myosin molecule). This conformational change causes the thick and thin filaments to move relative to each other - this is referred to as a "power stroke".
4. When another ATP molecule binds to the myosin it breaks the cross bridge and the heads revert back to their normal position. The process can begin again and cross bridge cycling occurs.
Why does rigour mortis happen?
As ATP is needed to break cross bridges and relax muscles, which can no longer be synthesised in dead people / animals.
Explain the regulation of the contractile process in skeletal muscle (Resting state vs Contraction)
Resting state: Tropomyosin is held over the myosin binding site by a troponin molecule, so even though the myosin is activated it can't get to it's binding site. This conformation occurs when there is no calcium present.
Contraction: When calcium is present it binds to the binding site on the troponin molecule which flips the tropomyosin away from the myosin binding site and myosin can bind with actin. Elevated calcium levels inside the cell exposes the myosin binding site which allows cross bridge cycling to occur, shortening the length of the muscle.
What is the name of the calcium intracellular store?
What are the differences between isometric and isotonic contraction?
Isometric: length of the muscle does not change, can contract muscles more but it doesn't change the muscle length, you just get more force being generated within the muscles, increased amount of tension generated within the muscle by generating more cross bridges
Isotonic: tension of muscle stays the same, length of muscle changes, thick and thin filaments move relative to each other
There is cross bridge cycling in both isometric and isotonic contraction