muscle Flashcards
cross bridge cycle steps
1.) Formation - myosin head binds to actin
2.) Power stroke - release of inorganic phosphate binds myosin to actin stronger, release of ADP causes power stroke
3.) Detachment - bind ATP releases myosin from actin
4.) Energisation of myosin head - hydrolysis of ATP causes myosin head to go to cocked position
myofibril structure
found inside myocyte
consist of sarcomeres joined end to end
so many myofibrils push nuclei out to side of myocyte
two types of smooth muscle units
single unit (electrically coupled as has gap junctions for signal to spread)
multi unit (electrically isolated) function individually
cardiac vs skeletal release of Ca2+ triggered by
cardiac - ligand (ca2+) gated ion channel ryanodine receptor as SR not continuous with sarcolemma
skeletal - voltage-gated ca2+ channel as SR is continuous with sarcolemma
two layers of smooth muscle in gut
circular layer closest to centre for contraction breaking down food
longitudinal layer for moving food along gut
smooth muscle structure vs skeletal and cardiac - ravioli
smooth muscle has caveolae instead of t tubules to increase SA, makes it easier for action potential to get into cell
smooth muscle contraction initiation vs skeletal and cardiac
ca2+ main source from SR for cardiac and skeletal
Troponin absent in smooth muscle instead has calmodulin which once activated by Ca2+ activates myosin light chain kinase
myosin light chain kinase phosphorylates light chains on myosin neck
what are varicosities?
in axon of sympathetic nerves innervating smooth muscle fibres, contain and release neurotransmitters to modulate smooth muscle contraction
smooth muscle vs cardiac and skeletal length tension relationship
smooth initial passive tension with stretch but relaxes over time
initiation of cardiac action potential
spontaneous depolarisation due to leak channels (Na+) or funny channels, when threshold reached, slow depolarisation due to voltage gated Ca+
