Module 4 Lecture 3

Question 1

What is excitation contraction coupling?

Answer 1

Conversion of an action potential to contraction; electrical signal to a mechanical force

Also known as EC coupling

Question 2

How does EC coupling work?

Answer 2

• Action potential runs along the myofibre which triggers the cross-bridge cycling

Key Pathway is required: T-tubule; invaginates into the fibre carrying with it the extracellular fluid

Action potential running down T-tubule is not in the cytoplasm, it is still in the ECF

Question 3

If the inside of the T-tubule is the ECF then what is the outside of the T-tubule membrane?

Answer 3

It is the inside of the cell

Question 4

How is the T-tubule structurally positioned?

Answer 4

Runs vertically down on either side of the protein rods of myosin

Question 5

What is the green like blanket that covers the sarcomere? What does it do?

Answer 5

The green blanket like structure is the sarcoplasmic reticulum & it is responsible for storing calcium

Question 6

How does the T-tubule inside the sarcoplasmic reticulum running down either side of the sarcomere communicate with the SR

Answer 6

The T-tubule brings the action potential to communicate inside to the sac to open channels that release calcium into the cytoplasm

Question 7

What is structure determines function & how does that relate to the SR and the T-tubule?

Answer 7

The organization of structures whether it be molecules or organelles determines how something may function

The way the T-tubule is organized to be inside the SR and running down it to communicate signals to the SR to release calcium is an example of how structure will determine the function

Question 8

Why is the sarcomere covered entirely with the SR and not specific parts?

Answer 8

So that the calcium released gets to every troponin on the sarcomere and causes the entire sarcomere to contract, not just part of it

Question 9

What are the lateral sacs?

Answer 9

Branch off the Sarcoplasmic Reticulum to cover the myofibril

Question 10

Explain what is happening in the image

Answer 10

The outside of the T-tubule (facing the cytoplasm) has dihydropyridine receptors (DHPR) which interacts with a protein receptor on the SR called the ryanodine receptor

• Ryanodine receptors are calcium releasing channels

Question 11

How does DHPR open the ryanodine?

Answer 11

Via an action potential

• Therefore you need an action potential to make the DHPR and the ryanodine receptor interact or else they’ll just be really close to each other without touching

DHPR is a voltage gated channels because it needs an action potential

Question 12

If the DHPR is a voltage gated channel, what does that make ryanodine since they both work together?

Answer 12

Ryanodine is a voltage gated calcium channel

Question 13

How is calcium removed from the troponin and taken up into the SR?

Answer 13

Through an ATP dependant pump, it drives calcium out of the cytoplasm back into the SR

Question 14

What are the three processes that require ATP in the process of muscle contraction. What are they?

Answer 14

1. The action potential - sodium/potassium pumps
2. Powering myosin to flex its head
3. To relax the muscle after contraction