Cardiac and smooth muscle Flashcards
How are cardiac myocytes differenct from other muscle
shorter, branched, and interconnected from end to end by structures called intercalated disks, visible as dark lines in the light microscope.
What are the desmosomes
things in the intercalated discs. that link adjacent cells mechanically,
what do the gap joints in intercalated disk do?
link adjacent cells electrically.
Cardiac muscle thus acts as a …. of coupled cells, unlike skeletal muscle fibers, which are separate cells bundled together by …..
Cardiac muscle thus acts as a mechanical and electrical syncytium of coupled cells, unlike skeletal muscle fibers, which are separate cells bundled together by connective tissue.
do the sacromeres of cardiac muscle contain thin and thick filaments
yes, similar array because striated
How is the iniation of cardiac contraction different from skeletal
own pacemaker, instead of neurons
what is the pacemaker of the heart
sinoatrial node.
do cardiac myocytes receive synaptic input from autonomic neurons? explain
yes, but the sympathetic and parasympathetic divisions of the autonomic nervous systemuse these synapses to modulate rather than to initiate electrical activity and contractile force of cardiac muscle.
How is the EC coupling of cardiac musle different
cardiac contraction has an absolute requirement for Ca 2+ influx through L-type Ca 2+ channels during the action potential.
is the t tubule network of heart different to skeletal
simialr, except that a single terminal cisterna of the SR forms a dyad junction with the T-tubule rather than a triad junction.
where are the T-tubules of cardiac myocytes located?
at the Z lines separating sarcomeres rather than at the A-I band junctions.
how does the hearth get suffiecient CA2+ for contraction
Ca 2+ influx through the L-type Ca 2+ channels alone is not, however, sufficient to initiate contraction. Rather, this increase in [Ca 2+ ] i leads to an opening of the RYR Ca 2+ -release channels in the SR membrane.
what is Ca 2+ -induced Ca 2+ release (CICR)
The resulting release of Ca 2+ from the SR amplifies the rise in [Ca 2+ ] i
is the contribution of CICR greater to the rise of Ca than L-type?
yes
what is different about troponin C in cardiac muscles
binds 3 Ca instead of 4 (skeletal)
what does phospholamban (PLN) do
inhibits SR Ca-pump activity
what does PKA do
phosphorylate PLN, so PLN ability to inhibit the SR Ca pump is lost.
what is epinephrine and what does it do
ctivators of PKA, such as the neurotransmitter epinephrine, may enhance the rate of cardiac myocyte relaxation.
is there frequency summation in cardiac muscle
no, Because cardiac muscle must contract only once with each heartbeat and must fully relax between each contraction,
what does norepinephrine mediate and is?
a neurotransmitter released by the sympathetic nervous system. that modulates the contractile force generated during each individual muscle twitch
is there multiple fiber summation at cardiac muscle
no, because the extensive electrical coupling between cardiac myocytes, as well as the requirement that cardiac muscle contract homogeneously
how is contractile function of cardiac muscle regulated
either by modulating the magnitude of the rise in [Ca 2+ ] i or by altering the Ca 2+ sensitivity of the regulatory proteins.
