Skeletal Muscles Flashcards
relaxed to contracted myofibril
actin slides into myosin filaments I band (light, actin) reduces in length A band (dark, actin + myosin) stays same length H zone (myosin) reduces in length
neuromuscular junction (acetylcholine)
action potential arrives at neurone
Ca2+ ion channels and Ca2+ diffuses into synaptic knob
vesicles fuse with pre synaptic membrane
AC is released and diffuses across synaptic cleft
binds to complementary receptors on sarcolemma
triggers Na+ VGIC to open and Na+ diffuse in
if depolarisation hits threshold, act pot is made
act pot passes along sarcolemma into sarco retic
causes Ca2+ to be released from sarco. retic.
muscle contraction
Ca2+ released from sarcoplasmic reticulum
causes tropomyosin to shift and reveal myosin binding sites on actin
myosin heads bind, creating actinomyosin bridges
hydrolysis of ATP causes myosin head to bend, moving actin and pulling it towards M line
ATP attaches to myosin head detaching it from actin
hydrolysis of ATP repositions myosin head
(ATPase- provides energy to reposition)
cycle repeats as Ca++ is still being released
slow twitch
contract slowly aerobic- 38 ATP lots of mitochondria lots of capillaries to provide o2 and glucose don't fatigue lots of myoglobin less glycogen smaller SR network little PC
fast twitch
contract quickly anaerobic- 4 ATP less mitochondria less capillaries fatigue quickly less myoglobin large glycogen stores large SR network lots of PC
ATP importance in contraction
detaches myosin head from actin
provides energy to reposition myosin head and to form actinomysoin crossbridges
causes active reuptake of ca2+ ions back to sr
stopping muscular contraction
removal of calcium ions
if no calcium binds then tropomyosin cannot be shifted so myosin binding sites are no longer exposed
lack of ATP- actinomyosin bridges can’t form, can’t detach and reposition myosin heads
can’t cause active reuptake of ca2+ to sarcoplasmic retic
