Topic 1 Flashcards
contractile apparatus of striated muscle is organized into –
sarcomere
How does skeletal muscle perform mechanical work?
via the skeleton under voluntary neural control
How does the cardiac muscle perform mechanical work?
has it’s own pacing control but modulated by ANS
How does smooth muscle perform mechanical work in target organ systems?
modulated by NT, metabolic, local and hormonal factors
How are myocytes organized?
in layers or syncytium which forms heart chambers
Describe how neurons from ANS innervate the heart.
innervate regions of specialized fibers (not individual myocytes)
How is the heart’s mechanical activity rhythmically paced?
from special pacemaker cells in SA node of right atrium (NT modification)
Where does striations of cardiac and skeletal muscle come from?
interdigitation of thick and thin filament proteins within sarcomere
What contributes to sarcomere organization and muscle function?
ECM and cytoskeleton
How are sarcomeres in skeletal muscle organized to form the whole muscle?
large fibers
How are sarcomeres in cardiac muscle organized?
syncytium of myocytes
What is the basis of striated muscle force generation and shortening?
sliding filament hypothesis
what is the molecular motor that generates force and movement in muscle?
myosin (specifically cross-bridges)
What reaction occurs to generate force?
ATP hydrolysis (chemomechanical transduction)
Explain the importance of the two S1 heads on myosin?
increases probability that myosin and actin bind/cycle (cooperativity)
What protein component generates the force in the actomyosin cross-bridge?
S1 head conformational change
How much force does the cross-bridge generate?
10 pN (10^-12 N)
How fat does cross-bridge move per ATP?
10 nm/CB cycle
with unregulated actin, crossbridges with cycle indefinitely under what circumstances?
enough ATP
myosin and actin in proximity
What element regulates striated muscle contraction?
Ca2+
tropomyosin and troponin lie along –
actin thin filament
binds to the long tropomyosin molecule every 7 actin molecules.
Troponin T
physically inhibits the binding of myosin to actin when no calcium is present.
Troponin I
binds calcium
Troponin C
When Ca2+ is bound, the conformation changes moving – off the myosin binding site on actin permitting crossbridge cycling
TnI
Describe Ca2+ binding sites on TnC
two Mg2+
two Ca2+ (only one functional in cardiac)
– regulation by troponin/tropomyosin complex
allosteric
the sequence of events that link the depolarization of the surface membrane with tension development by the contractile machinery.
excitation contraction coupling
Describe calcium source in humans and mammals?
70% from SR
30% outside
intracellular Ca2+ resequestered from SR by –
SR Ca2+ pump
rate of SR Ca2+ pump modulated by –
phospholamban
uses ATP
extracellular Ca2+ resequestered from myocyte by –
Na/Ca2+ exchanger and T-tubule Ca pump
describe intracellular Ca2+ levels for a relaxed cell
low
How does Ca2+ enter cell from outside?
through L-type Ca2+ channel (after an AP)
what does extracellular Ca2+ trigger?
release of more Ca2+ from SR
