Skeletal Muscle Flashcards
Lecture 9
A myofilament is primarily composed of
actin and myosin
Actin forms..
the thin filament
Actin forms the thin filament, a …
structural scaffold that runs along the myofilament
Myosin forms the..
thick filament
Function of myosin
Acts a motor molecule, attaching to actin and generating force to pull
When does actin and myosin bind together
when calcium is present
when calcium is present,
myosin and actin bind together
When actin and myosin bind together in the presence of calcium,
they form cross bridges and allow contraction to occur
1st step of cross bridge cycling
The myofilament has just finished a power stroke which is pulling on actin. Actin/myosin cross bridges are still present.
2nd part of cross bridge cycling
A molecule of ATP binds to the myosin, in preparation for releasing some energy to prime the myosin head.
The binding of ATP causes the myosin head to release actin… no more cross bridge!
3rd part of cross bridge cycling
The myosin head burns the ATP to make energy (and some ADP waste). It stores the energy by changing the shape o the myosin, getting it ready to pull on actin again.
4th part of cross bridge cycling
If calcium is present and bound to the myofilament, then it’s time for the next contraction. The energized myosin head can now bind to actin, forming a cross bridge.
last part of cross brideg cycling
There is now an energised myosin head attached to actin. The myosin uses its stored energy to pull, causing the actin filament to slide. The sacromere shortens,.. contraction has occurred.
Muscle tensions depends on what two things
- The number of muscle fibres recruited
- The rate at which the muscle is stimulated
Muscle tension: The number of fibres activated is regulated by..
how many neurons are active at one time
A small number of active neurons tends to produce low force from the muscle,
with the amount of force generally increasing as more neurons are activated.
The process of activating more fibres to make more force is called…
recruitment
Muscle tension - recruitment
The process of activating more fibres to make more force
Many action potential fired in a rapid sequence results in…
a sustained release of calcium from the sarcoplasmic reticulum, a sustained period of actin-myosin interaction and a sustained period of contraction.
Twitch
When a single action potential will result in a pulse of calcium release into the cytoplasm and a short period of tension development
Tetanus
Happens when we reach maximal signalling and contraction capability of the muscle, at which point the force will platueau.
Each muscle has an optimal length where…
it will be the strongest
What happens when the muscle is either shorter or longer than its optimal length
It will be weaker
What is the result of the changing overlap between the actin and myosin filaments
The length tension relationship where a muscle will have an optimal length where it is the strongest
What happens when there is not enough and too much overlap between the actin and myosin filaments
There won’t be a lot of cross bridges. Too much and there would be no space left to contract.
Fast fibres are mighty but…
fatigue quickly
Slow fibres supply…
steady force and are slow to tire
Fibre diameter of fast and slow fibres
Fast - large
Slow - small
capillary supply of fast and slow fibres
Fast - few
Slow - many
Mitochondria supply of fast and slow fibres
Fast - few
Slow - many
colour of fast and slow fibres
Fast - white
Slow.- Red
Fatigue resistance of fast and slow fibres
Fast - low
Slow - high
time to peak tension of fast and slow fibres
Fast - fast
Slow - slow
Explain how a contraction is produced
The myofilament proteins actin and myosin bind together when cellular calcium is high, creating cross bridges. Myosin then uses the energy liberated from ATP to pull on the actin filament, causing a contraction.
Skeletal muscle force generation depends on…
the number of fibres that contract (recruitment) and the frequency of stimulation, up to a maximum possible force (tetanus)
Muscles rich in fast fibres produce..
lots of force quickly thanks to their energy reserves, but they tire out quickly
Slow fibres are able to generate a lot of energy even while working..
so they are difficult to fatigue.
