Lecture 4-Skeletal Muscle Contraction Flashcards
A?

I-band
HI MA -> H-myosin only; I-actin only
B?

h-band
Contains both
C?

z-band
Anchors myosin (via titin)
Anchors actin filaments
D?
M-line: center of myosin filaments
E?

H-band: Myosin chain only
HI MA -> H-Myosin only; I-Actin only
What occurs (prior to the NMJ) to being contraction?
A.P. arrives at terminal bouton, opening voltage gated Ca2+ channels, Ca2+ influx causes NT vesicle to fuse with P.M.; ACh released into synaptic cleft
What is the result of N.T. binding to the motor end plate?
ACh binding to receptor causes ligand gated Na+ channel to open; Na+ influx produces A.P.
A.P. arrives at the ____ and opens the dihydropyridine-R (DHP-R)
T-tubule (invagination of the sarcolemma)
What occurs after depolarization of the DHP-R?
DHP-R interacts with Ca2+ channel on sarcoplasmic reticulum, prompting efflux of Ca2+ into the muscle cell
What is the f(x) of calcium release from the SR in muscle contraction?
Ca2+ binds to troponin-C; this produces a conformational changes to tryopomyosin, uncovering the active sites on actin
What “activates” the mysoin head?
ATP
ADP+Pi (after ATP hydrolysis) causes _______.
Conformational change to mysoin head; this results in binding of myosin head and A.S. on actin
When does the “powerstroke” occur?
With the loss of ADP from myosin head
What releases the myosin head from the actin active site?
Binding of ATP to myosin head
What is the change to cytosolic Ca2+ with opening of Ca2+ on the SR?
0.1 microMolar to 1 microMolar
How is the cytosolic [Ca2+] reduced?
Na/Ca2+ pump uses ATP to cause Ca2+ to be “taken up” into the SR
What is the conformation of DHP-R?
Voltage-gated L-type channel in quadruplets
What is the mechanism behind calsequestrin?
Binds Ca2+ in the SR, thereby setting up a favorable [Ca2+] gradient, making it easier to return Ca2+ to SR
How is myosin “reactivated?”
Hydrolysis of ATP-> ADP+Pi “cocks” the myosin head
Define “pre-load”
The load on a muscle while the muscle is relaxed (before contraction)
Define “afterload”
The load the muscle must work against
Isotonic contraction occurs when the muscle generates ____ force than the afterload
more
Isometric contraction occurs when the muscle generates ____ force than the afterload
less
Type of tension produced by preload
Passive


