HUBS Lecture 9 Flashcards
what is the myofilament primarily composed of
proteins actin and myosin
what is the function of actin
actin forms a structural scaffold that runs along the myofilament
what is the function and structure of myosin
myosin acts as a motor molecule, attaching to the actin and generating force to pull. myosin also has heads a the end of the filament that attach to the actin fibre when needed.
what does the attachment of more myosin heads mean for the pull force
increased pull force
what is a cross bridge
a cross bridge formed when actin and myosin bind together (when calcium is present)
what does myosin look like when at rest
the heads are laid backwards because they haven’t attached to the actin yet
how does the addition of calcium to the cytoplasm allow the myosin heads to bind to the actin
when the sarcomere needs to contact the calcium will move away a blocking protein that is attached to the myosin head and allow the myosin to bond to the actin
what does muscle tension depend on
the number of muscle fibres recruited and the rate at which the muscle is stimulated
how is the number of muscle fibres activated regulated
by how many neurons are active at one time
what is the process of activating more fibres to make more force called
recruitment
what does a single action potential result in
a pulse in Ca2+ release into the cytoplasm and a short period of tension development called a twitch
what do many action potentials fired in rapid sequence result in
a sustained release of Ca2+ from the SR and therefore a sustained period of actin-myosin interaction and a sustained period of contraction called summation
what is tetanus
the maximum signalling and contraction capability of the muscle at which the force plateaus
what does too little overlap between actin and myosin result in
not enough space for myosin heads to attach therefore few cross bridges and low force
what does too much overlap between actin and myosin result in
not space for the myosin to contract and therefore small contraction and low force
what are the two types of muscle fibres
fast and slow
what type of muscle fibre has large cells and can contract very fast and produce lots of contractile power
fast muscle fibre
what type of muscle fibre stores a lot of energy and why
fast muscle fibres because we need them to be ready to contract
what type of muscle fibre has smaller cells and doesn’t need to produce lots of power or be very fast and why
slow muscle fibres because they are involved in posture etc so they don’t need to be fast but we also don’t want them to get tired easily
why do slow muscle fibres need large amounts of blood
because we don’t want them to get tired quickly. these muscles are associated with posture so they are extremely fatigue resistant
describe the attached state of the cross-bridge cycle
the myofilament has just finished a power stroke (pulling on actin)
actin/myosin cross bridges are still present - this is the point right after your muscle has contracted, you’re ready to relax
describe the released state
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 so there is no more cross-bridge
describe the cocked state
the myosin head burns the 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
describe the cross-bridge state
if calcium is present and bound to the myofilament, then it’s time for the next contraction - the energised myosin head can now bind to actin forming a cross-bridge
describe the power-stroke state
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 and contraction has occurred
