skeletal muscles Flashcards
muscle structure
muscle fiber - a long tubular, multinucleate cell
cell membrane - sarcolemma
cytoplasm - sarcoplasm
endoplasmic reticulum - sarcoplasmic reticulum
myofibril - tubular membrane found organelles that is filled with protein filaments of actin and myosin
muscle cells fused together to form bundles of parallel muscle fibres (myofibrils)
arrangement ensures no point of weakness between cells
each bundle surrounded by endomycium - loose connective tissue with many capillaries
I band
light band where ONLY actin is present
A band
dark band where myosin is present
H zone
lighter region in the middle of the A band where there is ONLY myosin
how do the lengths of the bands differ when contracted
A band remands the same
I band gets shorter
H zone gets shorter
Z line
mid point between M lines
M line
middle of sarcomere
sarcomere
section inside myofibril made up of a vertical stack of atleast 4 thin and 1 thick filaments
actin
thin filament - wrapped with tropomyosin protein chain - binding sites under which are specific for myosin heads
calcium ions causes tropomyosin shape to change which exposes binding sites
allowing an actinomyosin bridge to form
depolarisation of muscle fibre
neuromuscular junction
nerve impulse passes from motor neurone to muscle fibre
- triggers depolarisation
- spreads across whole muscle fibre
depolarisation reaches sarcoplasmic endoreticulum - wrapped around muscle fibres (myofibrils)
depolarisation causes sarcoplasmic reticulum to release calcium ions into myofibrils
myosin
active site on myosin head
ATP hydrolysis (ATPase)
ratchet / sliding filament mechanism
calcium ions trigger tropomyosin to move away from binding sites on the actin
projecting from the myosin filament are myosin heads and these attach to the binding sites on the actin filament to form actino-myosin cross bridges
ADP and Pi released from myosin head - caused by a power stroke as a result of tension being caused
ATP molecule binds to myosin - bridge is broken as myosin head shape changes slightly so detaches from actin
within the sarcoplasm - enzyme ATPase - activated by the calcium ions to hydrolyse the ATP on the myosin head into ADP and released enough energy for myosin head to return to original position
starting position ready to bind again
what is phosphocreatine
stores in muscles - assists process as provides phosphate to regenerate ATP from ADP
phosphate store
phosphorylates ADP directly to ATP when oxygen or aerobic respiration is limited eg during vigorous exercise
slow-twitch fibres
structure - contains a large store of myoglobin, a rich blood supply and many mitochondria
location - calf muscles
contract slow
can respire aerobically for longer periods of time due to rich blood supply and myoglobin oxygen store
adapted for endurance work
fast-twitch fibres
structure - thicker and more myosin filaments, a large store of glycogen, a store of phosphocreatine to help make ATP from ADP and a high concentration of enzymes involved in anaerobic respiration
location - biceps
contract faster to provide burst of powerful contraction, adapted for intense exercise eg sprinting
