Module 4: Lecture 3

Question 1

A single cross-bridge can more your thin filaments how far?

Answer 1

a nanometer or two

Question 2

What is the process of excitation contraction coupling?

Answer 2

going from little amounts of Ca2+ inside the muscle cell to a a large amount of Ca2+ in the muscle cell

• excitation = action potential

Question 3

What is the transverse tubule or the T-tubule

Answer 3

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

Question 4

What is a sarcolemma?

Answer 4

another name for the cell membrane of a myo site

Question 5

What is your sarcoplasmic reticulum (SR)?

Answer 5

• mesh like structure
• has specialized sacs on either side called lateral sacs
• all the calcium is stored in the lateral sacs

Question 6

Where is all the calcium stored in out muscles?

Answer 6

• INTRACELLULARY
• in the lateral sacs of the SR

Question 7

Why would we want the calcium to be stored in the sarcoplasmic reticulum opposed to the cytosol?

Answer 7

We want the muscle to be relaxed, an influx of calcium would lead to muscle contractions

Question 8

What is terminal cisternae?

Answer 8

another word for lateral sacs

Question 9

Where is the terminal cisternae found?

Answer 9

Either side of the T-tubule are these enlarged SR which is referred to as the terminal cisternae

Question 10

What is involved in the triad?

Answer 10

• a single T-tuberle
• 2 lateral sacs
• key regulatory site for the release of calcium

Question 11

True or False
The T-tubles continuous with the Sarcolemma contains a high concentration of voltage gates sodium and potassium channels

Answer 11

True

Question 12

Why is the T-tubes so important for muscle contraction?

Answer 12

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

Question 13

What is the fundamental site for excitation contraction coupling?

Answer 13

Triad

Question 14

What receptor is on the lateral sacs of the SR that allows for the release of Ca2+?

Answer 14

• foot proteins
  aka
• Ryanodine receptor

Question 15

What are Ryanodine receptors?

Answer 15

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

Question 16

How are the Ryanodine receptors activated?

Answer 16

• 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

Question 17

What are Dihydropyridine receptors? (DHPR)

Answer 17

specialized channels that are voltage sensitive, aka they will open once a certain change in threshold is reached

• sits in clusters of 4

Question 18

What are the steps in the activation of muscle contractions?

Answer 18

1. Action potential travels down the T-tubule triggering the voltage sensitive channels (Dihydropyridine receptors) to activate
2. This activations of the DHPR allows the voltage gated channels on the terminal cisternae of the SR to open allowing the influx of calcium
3. Ca2+ will bind to the subunit C, inducing conformational change to troponin, releasing the inhibitory grip of tropomyosin
4. After tropomyosin leaves the binding site it is vacant for the myosin heads to bind
5. 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

Question 19

What does the SERCA pump stand for? and what is it?

Answer 19

• SarcoEndoplasmic reticulum calcium ATPase
• specialized protein removes calcium from the intercellular space back onto the lateral sacs

Question 20

Why is the SERCA pump called a pump?

Answer 20

because it utilizes ATP

• there is a huge amount of calcium in the cytosol which needs to actively go back into the SR

Question 21

Is the SERCA pump always active?

Answer 21

yes