Muscle 3 Flashcards
Action potentials propagate from the sarcolemma to the interior of muscle fibres along the…
t-tubule networks
initiation of muscle action potential
- motor neuron release ACh at neuromuscular junction
- net entry of Na+ through ACh receptor-channels initiate AP
DHP
dihydropyridine; L-type Ca2+ channel
RyR
ryanodine; ca2+ release channel on sarcoplasmic reticulum
excitation-contraction coupling
- AP in t-tubule alters conformation of DHP receptor
- DHP receptor opens RyR and Ca2+ enters cytoplasm
Besides mechanically, ryanodine receptors can also be activated by..
Calcium (calcium induced calcium release)
An increase in calcium conc. triggers….
contraction by removing the inhibition of cross bridge cycling
describe the removal of the inhibition of cross bridge cycling
- Calcium binds on troponin C, inducing conformation change in troponin conplex
- troponin complex and tropomyosin move and reveal myosin binding site on actin
4 steps of cross bridge cycling
- ATP binding
- ATP hydrolysis
- the power stroke
- ADP release
ATP binding
ATP binds to the head of myosin heavy chain, reducing affinity of myosin for actin
ATP hydrolysis
ATP is broken down to ADP and inorganic phosphate resulting in myosin head pivoting around hinged into cocked state
cocked state
when head is aligned with and binds to a new actin molecule on thin filament
the power stroke
dissociation of Pi from myosin head strengthens bon between actin and myosin and triggers power stroke; a conformational change in which myosin head returns to uncocked state and pulls actin filament generating force and motion
ADP release
dissociation of ADP from myosin causes myosin to remain bound to actin until ATO initiates the cycle again
Termination of contraction requires removal of…
Calcium
Calcium can be removed to the extracellular space by…
Na-Ca exchanger or by the Ca2+ pump which uses ATP
Calsequestrin and calreticulin
maximize Ca2+ uptake by the SR
Up to how many Ca2+ binding sites per molecule?
50
elastic recoil of titin and other connective tissue
causes sarcomeres to return to initial resting position
rigor mortis
development of rigid muscle several hours after death; Ca2+ leaks into sarcoplasm and binds troponin
SERCA pump
reuptake of Ca2+
When ATP production stops
- Ca2+ cannot be removed
- myosn head cannot be released from actin
- latched cross bridge formation
timing of E-C coupling
-delays between motor neuron AP and muscle fibre AP and between muscle fibre AP and contraction
sources of ATP
- free intracellular ATP
- stored as phosphocreatine
