cardiac muscle Flashcards
T or F: cardiac muscle is striated
T
How many nuclei are in cardiac muscle?
most of the time 1, sometimes 2
is cardiac muscle voluntary or involuntary
involuntary
T or F: intermediate filaments and dense bodies are only in cardiac muscle
F - smooth muscle
contractions of cardiac muscle produce…
pumping of heart chambers
cardiomyocytes are joined by…
intercalated discs (with desmosomes and gap junctions)
cardiac muscle are organized from units of …
myofibrils
T or F: cardiac muscle cells are autorhythmic
T
the ________ arrangement of ventricular muscle allows ventricular contraction to squeeze the blood upward from the apex of the heart
spiral
intercalated disks contain __________ that transfer force from cell to cell, and ________ that allow electrical signals to pass rapidly from cell to cell.
desmosomes
gap junctions
Do autorhythmic or contractile cells signal for contraction?
autorhythmic - they signal for contraction but don’t actually contract themselves, have smaller and fewer contractile fibers than contractile cells and do not have organized sarcomeres
T or F: cardiac and skeletal muscle are multi nucleiated
F, only skeletal
Does cardiac or skeletal have larger T-tubules
cardiac, they are larger and branch
Does cardiac or skeletal have larger sarcoplasmic reticulum?
skeletal, cardiac has a smaller and underdeveloped SR
mitochondria occupy _____ of cardiac cell volume
1/3
explain the steps in cardiac excitation contraction coupling
1 - action potential enters from adjacent cell
2 - voltage gated Ca+ channels open and Ca+ enters cell
3 - Ca+ induces Ca+ release through RyR
4 - local release causes Ca+ spark
5 - summed Ca+ sparks create a Ca+ signal
6 - Ca+ ions bind to troponin to initiate contraction
7 - relaxation occurs when Ca+ unbinds from troponin
8 - Ca+ is pumped back into the sarcoplasmic reticulum for storage
9 - Ca+ is exchanged with Na+ by the NCX antiporter
10 - Na+ gradient is maintained by the NaK ATPase
cardiac muscle contraction can be _______
graded
force generated in cardiac muscle contraction is proportional to ___________ and determined by ____________
proportional to number of active crossbridges
determined by how much Ca+ is bound to troponin
frank-starling relationship
sarcomere length affects force of contraction
- at rest cardiac muscle is not at optimal length, preload allows muscle to get closer to optimal length and allows for increased force production
T or F: cardiac muscle cannot undergo tetnus
T, you’d die
what is cardiac muscle’s resting membrane potential
-96 mV
cardiac depolarization occurs due to _______ inflow
Na+
initial repolarization of cardiac muscle occurs due to ____
Na+ channels close
the plateau period occurs due to:
Ca+ inflow
- sustains refractory period and prevents tetanus
the rapid repolarization of cardiac muscle is due to
K+ outflow (Ca+ channels close)
T or F: in cardiac muscle the refractory period lasts almost as long as the entire muscle twitch
T, long refractory periods in cardiac muscle prevents tetanus
the refractory period of skeletal muscle is a _______ of the muscle twitch and allows for ________
fraction
tetanus
What is the pathway for the conduction system of the heart?
SA node -> internodal pathways -> VA node -> AV bundle -> bundle branches -> purkinje fibers
autorhythmic cells have unstable membrane potentials called ______________
pacemaker potentials
at the beginning of a pacemaker potential _______ channels open and allow _______ to enter until an autorhythmic AP is triggered
leaky I f channels
Na+
(autorhythmic cells)
once an AP is triggered _______ channels close and ________ channels open allowing an influx of Ca+. At the peak ________ channels close and ______ channels open allowing an efflux of ________. K+ channels close and I f channels open again to start another cycle.
I f, Ca+
Ca+, K, K
myocardial autorhythmic cells have unstable membrane potentials called _______________
pacemaker potentials
depolarization of autorhythmic cells is initially due to ______ which allow _______ inflow
open I f channels
Na+
at threshold, 2nd type of voltage gated Ca+ channels open which leads to _________
steep depolarization
At peak of autorhythmic AP, _______- channels close, slow ______ channels open
Ca+ close, K+ open
which leads to decreased Ca+ inflow and increased K+ inflow.
pacemaker potential returns to lowest point
