Flashcards in cardiac muscle mechanics Deck (45)
do T tubules exist in cardiac muscle?
yes, they invaginate at the z-line
what is cardiac muscle called a "functional syncytium"?
because all the cardiac muscle cells are mechanically and electrically connected to one other- the entire tissue resembles 1 giant cell
why does cardiac muscle sarcoplasm have large numbers of mitrochondria and abundant reserves of myoglobin?
because the cells are dependent on aerobic metabolism to obtain energy needed to continue contracting
does this statement describe skeletal or cardiac muscle
"physical attachment between L type calcium channel and ryanodine receptors (the endfeet)"
how are the ryanodine receptors opened in cardiac muscle cells?
calcium induced calcium release
how long does a skeletal AP last? a cardiac AP?
skeletal- less than 5 msec
cardiac- around 250msec
can there be summation in cardiac muscle action potentials?
NO! the refractory period prevents it- heart contracts ONLY by twitch
what triggers phase 1 in a ventricle action potential?
closing of the Na+ channels
what 2 stages in ventricle action potential correspond to the absolute refractory period?
phase 1 & 2
how does phase 1 look on the graph?
slight dip (brief repolarization)
how does phase 2 look on the graph?
how do action potentials move between adjacent cells?
by means of charge displacement through gap junctions
what percentage of the necessary calcium for a twitch in a cardiac cell comes from outside the cell?
what percentage of the necessary calcium for a twitch in a cardiac cell comes from the SR in the cell?
how much external calcium contributes to skeletal muscle transients and twitch?
what method of calcium extraction from the sarcoplasm contributes the greatest to calcium removal?
sarcoplasmic and endoplasmic retiuculm ATPase (SERCA)
what percentage of sarcoplasmic calcium is removed via the sodium/calcium exchanger (NCX)?
besides NCX and SERCA what is the last "major" way to get ride of calcium in the sarcoplasm?
PCMA-pump that removes calcium from the cell
in cardiac muscle, where does calcium bind to initiate the crossbridge cycle?
when is the twitch in a cardiac muscle terminated?
when there is calcium clearance from the sarcoplasm
in cardiac muscle is there recruitment?
how long is the refractory period in an cardiac muscle cell action potential
what are two ways tension can be affected in cardiac muscle cells?
-by altering the sarcoplasmic [ca]-by an inotropic agent
-altering calcium sensitivity of the myofilament
withOUT vagal stimulation, what is the heart rate triggered spontaneously by the SA node?
with vagal stimulation, what is the heart rate triggered spontaneously by the SA node?
at what sarcomere length is the maximal force generated in the human heart?
an increase in initial length in cardiac muscle will do what to PO (maximum load)?
an increase in initial length in cardiac muscle will do what to velocity of shortening? amount of shortening?
an increase in initial length in cardiac muscle will do what to work the heart does? power delivered by the heart?