Skeletal Muscle: Contraction, Tension and Fibre Types Flashcards
What is actins role inside the muscle filament?
It forms the thin filament, and is a structural scaffold that runs along the myofilament. It is something that can be pulled on.
What is myosin’s role inside the muscle filament?
It forms the thick filament, acting as a motor molecule that grabs onto the actin and pulls (the myosin heads are what grab the actin).
When calcium is present, how do actin and myosin interact?
Myosin heads grab onto the actin, forming ross-bridges and allowing contraction to occur.
What is the attached state of Cross-Bridge cycling?
When the myofilament has just finished the power stroke and the actin/myosin cross bridges are still present
What is the released state of Cross-Bridge cycling?
When a molecule of ATP binds to the myosin, in preparation for releasing some energy to prep the myosin head.
Binding of the ATP causes the myosin head to release the actin so there is no more cross-bridge.
What is the cocked state of Cross-Bridge cycling?
The myosin head burns ATP to make energy (and some ADP waste). It stores the energy by changing the shape of the myosin, getting it ready to pull on actin again
What is the cross bridge state of Cross-Bridge cycling?
The calcium is present and bound to the myofilament, then it’s time for the next contraction.
Th energised myosin head can now bind to actin, forming a cross-bridge.
What is the power stroke state of Cross-Bridge cycling?
We now have a cross bridge with an energised myosin head attached to actin. The myosin uses its stored energy to pull, causing the actin filament to slide.
The sarcomere shortens, the contraction has occurred!
Muscle tension depends on what two things?
- The number of muscle fibres recruited
- The rate at which the muscle is stimulated
What does the number of fibres that are activated rely on?
It is regulated by the number of neurons that are active at one time
A small number of active neutrons = what?
Low force from the muscle
The process of activating more fibres to produce more force is called what?
Recruitment
What will a single action potential result in?
A pulse of Ca+ release into the cytoplasm, and a short period of tension development, called a twitch
What will many action potentials fired in a rapid sequence result in?
A sustained release of Ca+ from the SR, a sustained period of actin/myosin interaction, and a sustained period of contraction (twitch summation).
What happens when a muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between the stimuli?
We reach maximal signalling and contraction capacity of the muscle. The force will reach a plateau called the tetanus.
After this we either give up trying to lift whatever we were trying to lift, or the muscle just gives out.
