Mechanism Of Muscular Contraction Flashcards
(19 cards)
organize the structure of muscle
Contractile protein filaments are tethered within myofibrils –> myofibers or cells–> fascicles –> muscles
how does adult muscle growth occur
Adult muscle growth from some fusion of satellite cells into fibers, but mostly from synthesis of new myofibrillar proteins
differentiate embryonic, neonatal and adult myogenesis
embryonic forms the primary myogeneis which fuse to form the synthesis of new myofibrillar proteins forming scaffolds
neonatal is responsible for establishing the stellate cell niche as well as adult fiber type specification
adult is where the BM is assembled and you get the formation of the NMJ
what is the significance of the I band
the region where the thin filaments are not super imposed by the thick ones
what protein is responsible for tethering the thick and thin filaments
titin
which fibers (I or II) have the most myoglobin content?
which fibers are largest
which one are the most red in color
fiber type 1
fiber type II are twice as large
fiber 1 due to myoglobin (IIb stain the lightest)
what kind of channel is the receptor on the motor end plate
NA/K pump which pumps Na in and K out
which part of the NMJ does the esterase lie
motor end plate
what antiporter is responsible for the activation of the ACH release
what symporter is responsible for the activation of the ACH release
Ca- ACH release from presynaptic terminal
NA on the presynaptic terminal
what is the reason for latency phase in the electrochemical signaling of the NMJ
Latency due to time needed for Ca2+release from SR
how does the requires stimulus to fire change with the fiber size
smaller fibers are from small motor units and they require less stimulus to fire…. also remeber that the fast twich fibers are larger
the integrated of multiple fiber types allows graded contractile response
define fiber summation versus frequency summation
fiber summation Motor units may be recruited according to size, leading to stronger contraction
frequency summation Repeated stimulation at frequencies that do not allow time for sufficient calcium reuptake will produce stronger contraction with each stimulus (frequency summation) and result ultimately in a state of sustained contraction (tetanus/tetany)
what allows muscles to maintain constant tension
alternate firing of the motor units
describe the electrochemical basis for skeletal muscle contraction
depolarization activated the voltage-gated calcium channel, the dihydropyridine receptor (DHPR)–> brings in ca which then activates RYR1 (CSCR) on SR = release of ca into cytosole and into T tubule from SERCA = contraction
what stores the SR calcium
SERCA
What is the cascade of events that take place for a muscle to fire
Nerve AP
nerve release
muscle AP
muscle relase of Ca from SR
muscle contraction
what does the interaction of sliding filaments produce
cross bridge cycling
name something that helps the filaments in the myosin actin complex stay tethered in close proximity
myosin-binding protein C
how does contraction occur on the molecular level
this cross bidge cycling is ATP dependent and Ca regulated
ATP binding decreases the affinity
1- ATP binds to myosin and reduces its affinity for actin, allowing release of the rigor state.
2- Once ATP binds, it is hydrolyzed to ADP and a phosphate, both of which remain bound to the myosin head.
3- Once calcium becomes available, it binds troponin C and causes the conformational shift in tropomyosin that will allow actin-myosin binding.
4- The weak initial binding of actin and myosin in the presence of calcium triggers release of the phosphate residue –> concomittent strong binding of actin/myosin and triggers a power stroke.
3- ADP is released during the power stroke as well, leaving the myosin bound once more to actin.
Removal of calcium leaves myosin and actin chains bounds together until the next ATP binds the myosin head. This completes the cycle, and means we have now described both electrochemical and physiochemical properties of skeletal muscle that allow the cross bridge cycling that we see as muscle contraction, and have completed the excitation contraction coupling that ties the electrical, chemical, and mechanical responses in skeletal muscle.
If no ATP is present, the bound myosin retains its high affinity for actin, and will remain locked to it in a state of rigor. This is not likely to happen in a living being, as ATP levels are tightly managed and ATP is thus available.
