L10 Skeletal Muscle I Flashcards
Muscle fibers are made up of ?
Myofibrils
Myofibrils are made up of?
Sarcomeres
A sarcomere extends from what to what
Z line to z line
What is in the middle of the sarcomere
M line (in middle of A band)
Which band in the sarcomere is dark and which band is light
A band is dark - myosin
I band is light -actin
Does the M line ever contain actin?
No. ACtin never goes that far in
What is E-C coupling?
Electrical stimulus (action potential) converted to mechanical response (contraction)
t-tubules are a continuation of____
The sarcolemma
DHP (dihydropyridine) receptors in the T-tubules respond to what?
Changes in VOLTAGE
Even though they are called “receptors,” it is voltage they respond to not a chemical
What is a “triad”
Proximity of the cisternae of two sarcoplasmic reticulum membranes and a T-tubule
What are RYR (ryanodine receptors)?
Calcium release channels in the SR
Where are DHP receptors vs RYR receptors?
DHP in T-tubules
RYR in SR
In the wine bottle-cork analogy, what is the cork and which is the wine bottle?
Cork is DHP
Wine bottle is RYR
How does the “cork” (DHP) get removed from the “wine bottle” (RYR)?
At rest, there are amino acids on DHP that block the Calcium channels on RYR. When an action potential flows down the T-tubules, the DHP detects the voltage change, and those amino acids change conformation, moving out of the way. The Calcium within the SR flows (from high concentration to low concentration) out of the SR through the RYR and out into the muscle
WHat three proteins make up the actin complex?
Actin
Tropomyosin
Troponin
What determines the strength of the contractile force?
The number of cross-bridges formed
What must happen in order for the myosin head to bend and “stroke”
PHOSOPHATE must be released
The phosphate that came from the hydrolysis of ATP when you “reset” the head and ADP and Pi are just sitting there
What is required for the myosin and actin to detach
A fresh ATP
Does the A band change width during contraction?
No
The A band is the myosin filaments, they do not shorten
Does the I band shorten during contraction?
Yes
Does the H band shorten during contraction?
Yes
How does Calcium get back into the SR when the muscle contraction is over?
Sarcoplasmic Reticulum Calcium ATPase (SERCA)
Uses ATP to to move calcium against its concentration gradient
