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68 Cards in this Set

  • Front
  • Back
what type of muscle is cardiac muscle?
striated
how does cardiac muscle differ from skeletal muscle?
has intercalated discs with desmosomes, gap junctions, has functional syncytium, huge mitochondria, extensive branching & variations in diameter that alter the arrangement of sarcomeres
what are intercalated discs?
discs that consist of desmosomes and gap junctions that enable the transmission of current across the heart
what are desmosomes?
physical anchors that prevent adjacent cells from separating during contraction
what prevents adjacent cells from separating during contraction?
desmosomes
what are gap junctions?
intercellular connections that enable the passage of ionic current from cell to cell
what transmits current across the heart?
intercalated discs
what do desmosomes and gap junctions form?
intercalated discs
what are the intercellular connections that enable the passage of ionic current from cell to cell?
gap junctions
what is myocardium?
heart muscle
what do gap junctions do?
couple the ionic basis of excitation contraction coupling between adjacent cells
what is a functional syncytium?
a single coordinated unit
what term means the myocardium acts as a single coordinated unit?
functional syncytium
how do mitochondria differ in cardiac muscle compared to skeletal muscle?
huge, occupy 25-35% of the volume of cardiac cells (2% in skeletal muscle)
what is the volume of a cardiac cell filled with?
25-35% mitochondria, most remaining volume with sarcomeres composed of the same filaments as those in skeletal muscles
how does the arrangement of sarcomeres in cardiac muslce differ from skeletal muscles?
the myofibrils of cardiac muscle cells vary in diameter and branch extensively, accommodating the larger mitochondria lying between them (less dramatic banding patttern than in skeletal m)
the system for delivering calcium ions to the contractile elemens is BLANK elaborate in cardiac muscle than in skeletal muscle
less
what is different in the calcium ion delivery system in cardiac muscle vs skeletal muscle?
T-tubules are wider and fewer, entering the cell only once per sarcomere at the Z-discs, the SR is simpler and lacks terminal cisternae, resulting in no triads
what do T-tubules look like in cardiac muscle vs skeletal muscle?
wider and fewer
how do T-tubules enter cells in cardiac muscle?
once per sarcomere at the Z-discs
what does the cardiac muscle lack compared to skeletal muscle?
lacks terminal cisternae (because SR is simpler) and triads
what is different in the excitation-contraction coupling of cardiac muscle vs skeletal muscle?
automaticity (autorhythmicity) as a means of stimulation vs nerves, syncytial vs motor unity, and 250msec vs 1-2msec of absolute refractory period
what is the means of stimulation of cardiac muscle?
automaticity (autorhythmicity)
what is the means of stimulation of skeletal muscle?
nerves
what is the contraction unit of cardiac muscle?
syncytial
what is the contraction unit of skeletal muscle?
as motor units
what is the length of absolute refractory period of cardiac muscle?
250msec
what is the length of absolute refractory period of skeletal muscle?
1-2msec
what triggers cardiac muscle contractions?
action potential
what triggers skeletal muscle contractions?
action potential
What initiates a wave of depolarization in cardiac muscle?
spontaneous depolarization
how is depolarization transmitted?
cell-to-cell via gap junctions
how does the subsequent contractions of cardiac muscle occur?
in a mechanical sequence that optimizes the ejection of blood when initiating impulse is generated from the appropriate pacing center and spreads over the myocardium along the normal pathway
what is the pacing center?
the spontaneous depolarizing cells
how many myocardial cells have the spontaneous depolarizing feature?
~1% of cardiac fibers, remaining fibers are contractile elements
how does a fast cardiac AP begin?
at phase 0 the initial upstrake of the AP occurs when depolarization opens voltage-gated fast Na+ channels
what happens in a fast cardiac AP after voltage-gated fast Na+ channels open?
extracellular Na+ briefly enters the cell triggering depolarization of the membrane potential until the Na channels are inactivated
what causes a plateau in the fast cardiac AP?
the inward flux of Ca++ (10-20% of total Ca++ necessary for triggering contraction) through slow Ca++ channels that were opened by the same voltage that opened the Na+ channels (they are called slow because their opening is delayed)
what occurs in the ventricular myocardial cell after slow Ca++ channels open?
the influx of Ca++ stimulates the release of Ca++ (the remaining required) from the SR
what is the role of potasium in fast cardiac AP?
fast K+ channels open wih NA+ flux, then close quickly while slow K+ channel opens and enables K+ flus that decreases membrane potential
what occurs if Ca++ channels are open during a fast cardiac AP?
Ca++ continues to enter and cells continue to contract
when does tension development by myocardial cells occur?
during the plateau and peaks after the plateau ends because the entry of extracellular Ca++ is the initiating event on coupling contractile activity to depolarization
do cardiac muscles undergo summation?
No!
can tetanus occur with repeated stimulation in cardiac muscles?
No!
do cardiac muscle contractions get stronger?
no, they are at the same tension (but the tension may be altered by autonomic nervous system input
what can skeletal muscle do that cardiac muscle can't?
form stronger contractions using summation and recruitment
what events occur supsequent to depolarization?
calcium exits the cell
how does Ca++ enter myocardial cells?
through voltage-gated dihydropyridine (DHP) receptor
what does DHP stand for?
dihydropyridine (a voltage gated receptor)
how does the secondary increase in cytoplasmic Ca++ occur in myocardial cells?
ryanodine (Ry) receptors
what does Ry stand for?
ryanodine receptor
how are DHP and Ry receptors coupled in skeletal muscles?
mechanically
how are DHP and Ry receptors coupled in cardiac muscles?
calcium-induced calcium release
what is calcium induced calcium release?
when the extracellular Ca++ enering through DHP channeles triggers the opening of the Ry channel (in cardiac muscles)
calcium-induced calcium release occurs where?
between the DHP and Ry receptors coupled in cardiac muscle
what is a Ca++ signal created from?
summed Ca++ sparks (release events) that establish an intracellular Ca++ concentration sufficient to bind troponin and initiate the interaction beteen myosin and actin that contract muscles
what do Ca++ sparks do?
create a Ca++ signal that establishes an intracellular Ca++ concentration sufficient to bind troponin and initiate the interaction beteen myosin and actin that contract muscles
what is necessary to initiate interactions between myosin and actin?
a Ca++ signal that establishes an intracellular Ca++ concentration that binds troponin
what do myosin and actin do?
shorten the muscle similar to skeletal muscle
when does muscle relaxation occur?
when the cytosolic Ca++ concentration becomes insufficient for sustained interactions with troponin
what happens when cytosolic Ca++ concentration becomes insufficient for sustains interactions with troponin?
relaxation occurs
how does fre Ca++ concentration decrease?
Ca++ ATPase & cell membrane Na+/K+ ATPase
what does Ca++ ATPase do?
pumps Ca++ back into the SR
what does SR stand for?
sarcoplasmic reticulem
what does cell membrane Na+/K+ ATPase do?
pumps Na+ out and K+ in that ultimately enables Ca++ (2) exchange for Na+ (3)
becaues cardiac muscle contains a lot of mitochondria, it is intolerant of what?
oxygen debt
because cardiac muscle is intolerant of oxygen debt, what is the rule of metabolism?
aerobic
because cardiac muscle relies on aerobic metabolism, it can do what?
oxidize a wide array of energy molecules depending on what is available