Module 4: Lecture 3 Flashcards
A single cross-bridge can more your thin filaments how far?
a nanometer or two
What is the process of excitation contraction coupling?
going from little amounts of Ca2+ inside the muscle cell to a a large amount of Ca2+ in the muscle cell
- excitation = action potential
What is the transverse tubule or the T-tubule
a link from the outside of the cell to the inner core of the muscle fibre
- it is a part of the sarcolemma that dips down and makes a “U” shape
What is a sarcolemma?
another name for the cell membrane of a myo site
What is your sarcoplasmic reticulum (SR)?
- mesh like structure
- has specialized sacs on either side called lateral sacs
- all the calcium is stored in the lateral sacs
Where is all the calcium stored in out muscles?
- INTRACELLULARY
- in the lateral sacs of the SR
Why would we want the calcium to be stored in the sarcoplasmic reticulum opposed to the cytosol?
We want the muscle to be relaxed, an influx of calcium would lead to muscle contractions
What is terminal cisternae?
another word for lateral sacs
Where is the terminal cisternae found?
Either side of the T-tubule are these enlarged SR which is referred to as the terminal cisternae
What is involved in the triad?
- a single T-tuberle
- 2 lateral sacs
- key regulatory site for the release of calcium
True or False
The T-tubles continuous with the Sarcolemma contains a high concentration of voltage gates sodium and potassium channels
True
Why is the T-tubes so important for muscle contraction?
Since the T-tubles go into the myosite and can reach all the different myofibrils, the release of calcium is evenly distributed to all your myofibrils
What is the fundamental site for excitation contraction coupling?
Triad
What receptor is on the lateral sacs of the SR that allows for the release of Ca2+?
- foot proteins
aka - Ryanodine receptor
What are Ryanodine receptors?
they are gated channels that are closed at rest
- if that channel is open, it will allow calcium to exit via following it’s electrochemical gradient
How are the Ryanodine receptors activated?
- they sit in these tetrapods (aka clustered groups of 4 channels)
- they are physically linked with the Dihydropyridine receptors that rest on the T-tuble (also in clusters of 4)
- As the DHPR is activated via change in membrane potential that allows the Ryanodine receptors to open allowing calcium to leave the SR
What are Dihydropyridine receptors? (DHPR)
specialized channels that are voltage sensitive, aka they will open once a certain change in threshold is reached
- sits in clusters of 4
What are the steps in the activation of muscle contractions?
- Action potential travels down the T-tubule triggering the voltage sensitive channels (Dihydropyridine receptors) to activate
- This activations of the DHPR allows the voltage gated channels on the terminal cisternae of the SR to open allowing the influx of calcium
- Ca2+ will bind to the subunit C, inducing conformational change to troponin, releasing the inhibitory grip of tropomyosin
- After tropomyosin leaves the binding site it is vacant for the myosin heads to bind
- Remove calcium from troponin C to allow tropomyosin to renter and block the myosin site of the thin filaments to stop the cross-bridges from forming
What does the SERCA pump stand for? and what is it?
- SarcoEndoplasmic reticulum calcium ATPase
- specialized protein removes calcium from the intercellular space back onto the lateral sacs
Why is the SERCA pump called a pump?
because it utilizes ATP
- there is a huge amount of calcium in the cytosol which needs to actively go back into the SR
Is the SERCA pump always active?
yes
